Non-Crimp Fabric Composites: Manufacturing, Properties and Applications

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Non-crimp fabric composites

© Woodhead Publishing Limited, 2011

Related titles: Creep and fatigue in polymer matrix composites (ISBN 978-1-84569-656-6) Creep and fatigue in polymer matrix composites reviews ways of modelling creep and fatigue in polymer matrix composites with the aim of predicting and preventing failure. Part I focuses on viscoelastic and viscoplastic modelling. Part II covers environmental effects and stress corrosion, while Part III analyses creep rupture and damage interaction. Part IV investigates fatigue modelling and characterization and Part V covers the monitoring of creep and fatigue. Physical properties and applications of polymer nanocomposites (ISBN 978-1-84569-672-6) Polymer nanocomposites are polymer matrices reinforced with nanoscale fillers. Understanding the physical properties of polymer nanocomposites is a key factor in gaining wider uptake of the materials in new applications. The book is divided into sections covering polymer/nanoparticle composites, polymer/nanoplatelet composites and polymer/nanotube composites. It finishes by reviewing the range of applications for these important new materials. Fatigue life prediction of composites and composite structures (ISBN 978-1-84569-525-5) Fatigue is the progressive and localised structural damage that occurs when a material is subjected to cyclic loading. The use of composites is growing in structural applications and there is a need to understand how they respond to loading. This authoritative book reviews ways of predicting the service life of composites subjected to variable amplitude, multiaxial and other types of loading.

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Non-crimp fabric composites Manufacturing, properties and applications Edited by Stepan V. Lomov

Oxford

Cambridge

Philadelphia

New Delhi


Published by Woodhead Publishing Limited, 80 High Street, Sawston, Cambridge CB22 3HJ, UK www.woodheadpublishing.com Woodhead Publishing, 1518 Walnut Street, Suite 1100, Philadelphia, PA 19102–3406, USA Woodhead Publishing India Private Limited, G-2, Vardaan House, 7/28 Ansari Road, Daryaganj, New Delhi – 110002, India www.woodheadpublishingindia.com First published 2011, Woodhead Publishing Limited © Woodhead Publishing Limited, 2011 The authors have asserted their moral rights. This book contains information obtained from authentic and highly regarded sources. Reprinted material is quoted with permission, and sources are indicated. Reasonable efforts have been made to publish reliable data and information, but the authors and the publisher cannot assume responsibility for the validity of all materials. Neither the authors nor the publisher, nor anyone else associated with this publication, shall be liable for any loss, damage or liability directly or indirectly caused or alleged to be caused by this book. Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming and recording, or by any information storage or retrieval system, without permission in writing from Woodhead Publishing Limited. The consent of Woodhead Publishing Limited does not extend to copying for general distribution, for promotion, for creating new works, or for resale. Specific permission must be obtained in writing from Woodhead Publishing Limited for such copying. Trademark notice: product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation, without intent to infringe. British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library. ISBN 978-1-84569-762-4 (print) ISBN 978-0-85709-253-3 (e-book) The publisher’s policy is to use permanent paper from mills that operate a sustainable forestry policy, and which has been manufactured from pulp which is processed using acid-free and elemental chlorine-free practices. Furthermore, the publisher ensures that the text paper and cover board used have met acceptable environmental accreditation standards. Typeset by RefineCatch Limited, Bungay, Suffolk Printed by TJI Digital, Padstow, Cornwall, UK


Contents

Contributor contact details Introduction

xiii xvi

Part I

Manufacturing of non-crimp fabrics

1

1

Production of non-crimp fabrics for composites

3

A. SCHNABEL and T. GRIES, Institut für Textiltechnik (ITA) of RWTH Aachen University, Germany

1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 1.10

Introduction Warp-knitted non-crimp fabric (NCF) Weft-knitted NCF Non-crimp woven fabrics 3D woven and non-interlaced NCF Fixation by adhesion Comparison of production technologies Future trends Acknowledgements References

3 5 22 23 27 30 33 35 37 37

2

Standardisation of production technologies for non-crimp fabric composites

42

F. KRUSE and T. GRIES, Institut für Textiltechnik (ITA) of RWTH Aachen University, Germany

2.1 2.2 2.3 2.4 2.5

Introduction Classification and standardisation of non-crimp fabric (NCF) production methods Outstanding patents of existing machines for the production of NCFs The ‘Hexcel patent’ – EP 0972102 B1 Product patents in the production of NCFs

42 42 47 59 61

v © Woodhead Publishing Limited, 2011

vi

Contents

2.6

Immobilisation of adhesive on the surface of semi-finished textile products (DE 102008004112 A1) References

64 65

Structural stitching of non-crimp fabric preforms for composites

67

2.7 3

P. MITSCHANG, Institut für Verbundwerkstoffe GmbH, Germany

3.1 3.2 3.3 3.4 3.5 3.6

Introduction Threads for structural stitching technology Stitching technology and sewing machines Quality aspects for structural stitching Applications and future trends References

67 68 70 74 81 82

4

Understanding and modelling the effect of stitching on the geometry of non-crimp fabrics

84

S. V. LOMOV, Katholieke Universiteit Leuven, Belgium

4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8

Introduction General parameters of the fibrous plies Geometry of the stitching Distortions of fibres in the plies Change of the geometry after shear A geometrical model of NCF Conclusion References

84 85 86 92 98 100 100 102

5

Automated analysis of defects in non-crimp fabrics for composites

103

M. SCHNEIDER, Toho Tenax Europe GmbH, Germany

5.1 5.2 5.3 5.4 5.5

Motivation Quality characteristics of non-crimp fabric (NCF) Quality analysis of NCF by digital image analysis Future trends References

Part II Manufacturing of non-crimp fabric composites 6

Deformability of textile preforms in the manufacture of non-crimp fabric composites

103 104 106 111 114 115

117

S. V. LOMOV, Katholieke Universiteit Leuven, Belgium

6.1

Introduction

117


Contents

vii

6.2 6.3 6.4 6.5 6.6 6.7

Shear Biaxial tension Compression Bending Conclusion References

118 128 132 136 139 141

7

Modelling the deformability of biaxial non-crimp fabric composites

144

P. HARRISON, University of Glasgow, UK, W-R. YU, Seoul National University, Korea and A. C. LONG, University of Nottingham, UK

7.1 7.2 7.3 7.4 7.5 7.6 7.7 7.8

Introduction Behaviour of fabric architecture on the shear and draping behaviour of non-crimp fabrics (NCFs) Modelling strategies for NCF forming Energy-based kinematic mapping Finite element modelling of forming for NCFs Future trends Further information and advice References

144 145 148 149 156 161 162 162

8

Permeability of non-crimp fabric preforms

166

R. LOENDERSLOOT, University of Twente, The Netherlands

8.1 8.2 8.3 8.4 8.5 8.6 8.7 8.8

Introduction Experimental permeability results Geometric effects Deformation and permeability Conclusions Acknowledgements References Appendix: nomenclature

166 168 187 196 208 209 210 214

9

Understanding variability in the permeability of non-crimp fabric composite reinforcements

216

A. ENDRUWEIT and A. C. LONG, University of Nottingham, UK

9.1 9.2 9.3 9.4 9.5 9.6

Introduction Material characterisation Permeability measurement Modelling and simulation Future trends References


216 217 222 233 239 239

viii

Contents

10

Modelling of the permeability of non-crimp fabrics for composites

242

B. VERLEYE, S. V. LOMOV and D. ROOSE, Katholieke Universiteit Leuven, Belgium

10.1 10.2 10.3 10.4 10.5 10.6 10.7 10.8

Introduction Numerical simulation Experimental validation Parametric study Influence of shear Conclusion Acknowledgements References

Part III Properties of non-crimp fabric composites 11

Mechanical properties of non-crimp fabric (NCF) based composites: stiffness and strength

242 246 251 253 256 257 257 258 261

263

S. V. LOMOV, T. TRUONG CHI and I. VERPOEST, Katholieke Universiteit Leuven, Belgium

11.1 11.2 11.3 11.4

11.6 11.7 11.8 11.9 11.10

Introduction Materials and composite production Test procedures Mechanical properties of non-crimp fabric (NCF) composites Mechanical properties of composites based on sheared MMCF Damage development in B2 (0°/90°) laminates X-ray radiography Damage initiation in non-sheared and sheared materials Conclusions References

274 279 283 285 286 287

12

Damage progression in non-crimp fabric composites

289

11.5

263 264 265 266

L. E. ASP, J. VARNA and E. MARKLUND, Swerea SICOMP and Luleå University of Technology, Sweden

12.1 12.2 12.3 12.4 12.5

Introduction Damage progression in non-crimp fabric (NCF) composites due to in-plane loading Damage progression in impacted NCF composites Conclusions References


289 290 300 308 308

Contents

13

Fatigue in non-crimp fabric composites

ix

310

K. VALLONS, Katholieke Universiteit Leuven, Belgium

13.1 13.2 13.3 13.4 13.5 13.6

Introduction Fatigue in non-crimp fabric (NCF) composites Post-fatigue residual properties Conclusions and open questions References Appendix

310 311 330 332 332 333

14

Mechanical properties of structurally stitched non-crimp fabric composites

335

N. HIMMEL, Institut für Verbundwerkstoffe GmbH, Germany and H. HEß, BASF Engineering Plastics Europe, Germany

14.1 14.2 14.3 14.4 14.5 14.6 15

Introduction Materials and stitching configurations Characterisation of structurally stitched NCF laminates Simulation of mechanical behaviour of structurally stitched laminates Conclusions and future trends References Predicting the effect of stitching on the mechanical properties and damage of non-crimp fabric composites: finite element analysis

335 337 341 348 354 355

360

D. S. IVANOV, S. V. LOMOV and I. VERPOEST, Katholieke Universiteit Leuven, Belgium

15.1 15.2 15.3 15.4 15.5 15.6 16

Introduction Representative volume element (RVE) of non-crimp fabric (NCF) composites Elastic analysis Damage accumulation in NCF composites Conclusions References

360 363 369 372 383 384

Modelling drape, stress and impact behaviour of non-crimp fabric composites

386

A. K. PICKETT, University of Stuttgart, Germany

16.1 16.2 16.3 16.4

Finite element (FE) methods for drape, stress and impact analysis Laminate analysis and FE stiffness for non-crimp fabric (NCF) FE methods for infusion analysis Draping and FE simulation


386 387 389 390

x

Contents

16.5 16.6 16.7 16.8

Infusion simulation Stiffness and failure Impact and failure References

394 394 396 400

17

Modelling stiffness and strength of non-crimp fabric composites: semi-laminar analysis

402

E. MARKLUND, J. VARNA and L. E. ASP, Swerea SICOMP and Luleå University of Technology, Sweden

17.1 17.2 17.3 17.4 17.5

Introduction Stiffness models Strength models for non-crimp fabric (NCF) composites Conclusions References

402 405 420 435 436

Part IV Applications of non-crimp fabric composites

439

18

441

Aerospace applications of non-crimp fabric composites P. MIDDENDORF and C. METZNER, EADS Innovation Works, Germany

18.1 18.2 18.3 18.4 18.5

Introduction Aeronautic requirements Application examples Future trends References

441 443 445 447 448

19

Non-crimp fabric: preforming analysis for helicopter applications

449

F. DUMONT and C. WEIMER, Eurocopter Deutschland GmbH, Germany

19.1 19.2 19.3 19.4 19.5 19.6 20

Introduction Preform techniques for non-crimp fabrics (NCFs) Main NCF deformation mechanism observed during preforming Preforming defect analysis Conclusion and future trends References

449 449 454 456 458 460

Automotive applications of non-crimp fabric composites

461

B. SKÖCK-HARTMANN and T. GRIES, Institut für Textiltechnik (ITA) of RWTH Aachen University, Germany

20.1 20.2

Introduction Applications of non-crimp fabrics (NCF) in the automotive industry


461 466

Contents

20.3

xi

20.4 20.5 20.6

Research and development for the use of NCF in automotive applications Future trends Conclusion References

469 476 478 479

21

Non-crimp fabric composites in wind turbines

481

G. ADOLPHS and C. SKINNER, OCV Technical Fabrics, Belgium

21.1 21.2 21.3 21.4 21.5 22

Introduction Development of non-crimp fabric (NCF) composites in wind energy NCF materials used in nacelle construction Future trends References

481 483 491 492 493

Cost analysis in using non-crimp fabric composites in engineering applications

494

P. SCHUBEL, University of Nottingham, UK

22.1 22.2 22.3 22.4 22.5 22.6

Introduction Costing methodologies: current approaches Technical cost modelling Case study: 40 m wind turbine blade shell Acknowledgements References

494 495 496 504 509 509

Index

511


Contributor contact details

(* = main contact)

Chapter 1

Chapters 4, 6 and 11

A. Schnabel* and T. Gries Institut für Textiltechnik (ITA) of RWTH Aachen University Otto-Blumenthal-Strasse 1 52074 Aachen Germany

S. V. Lomov Department of Metallurgy and Materials Engineering Katholieke Universiteit Leuven Kasteelpark Arenberg 44 bus 2450 B-3001 Heverlee (Leuven) Belgium

e-mail: [email protected]; thomas.gries@ita. rwth-aachen.de

e-mail: [email protected]

Chapter 5 Chapter 2 F. Kruse* and T. Gries Institut für Textiltechnik (ITA) of RWTH Aachen University Otto-Blumenthal-Strasse 1 52074 Aachen Germany e-mail: [email protected]; [email protected]

Chapter 3 P. Mitschang Manufacturing Science Institut für Verbundwerkstoffe GmbH Erwin-Schroedinger-Strasse 58 67663 Kaiserslautern Germany

M. Schneider Toho Tenax Europe GmbH Kasinostrasse 19–21 42103 Wuppertal Germany e-mail: [email protected]

Chapter 7 P. Harrison* University of Glasgow School of Engineering University Avenue Glasgow G12 8QQ UK e-mail: [email protected]

e-mail: [email protected]

xiii © Woodhead Publishing Limited, 2011

xiv


W-R. Yu Seoul National University Department of Materials Science and Engineering Gwanak _ 599 Gwanak-ro Gwanak-gu Seoul 151–742 Korea A. C. Long University of Nottingham Faculty of Engineering University Park Nottingham NG7 2RD UK

Chapter 8 R. Loendersloot University of Twente Faculty of Engineering Technology – Applied Mechanics & Production Technology P.O. Box 217 7500 AE Enschede The Netherlands e-mail: [email protected]

Chapter 9 A. Endruweit and A. C. Long* Faculty of Engineering (M3) – Division of Materials, Mechanics and Structures University of Nottingham University Park Nottingham NG7 2RD UK e-mail: [email protected]

Chapter 10 B. Verleye*, S. V. Lomov and D. Roose

Katholieke Universiteit Leuven Celestijnenlaan 200A B-3001 Leuven Belgium e-mail: [email protected]

Chapter 12 L. E. Asp* and E. Marklund Swerea SICOMP AB Box 104 SE-43122 Mölndal Sweden e-mail: [email protected]; erik. [email protected]

J. Varna Div. Polymer Engineering Luleå University of Technology SE-97187 Luleå Sweden e-mail: [email protected]

Chapter 13 K. Vallons Department of Metallurgy and Materials Engineering Katholieke Universiteit Leuven Kasteelpark Arenberg 44 bus 2450 B-3001 Heverlee Belgium e-mail: [email protected]

Chapter 14 N. Himmel* Institut für Verbundwerkstoffe GmbH (Institute of Composite Materials) University of Kaiserlautern Erwin-Schrödinger-Strasse 67663 Kaiserlautern Germany e-mail: [email protected]



H. Hess BASF Engineering Plastics Europe 67056 Ludwigshafen Germany

xv

D-81663 Munich Germany e-mail: [email protected]

Chapter 19 Chapter 15 D. S. Ivanov, S. Lomov and I. Verpoest Department of Metallurgy and Materials Engineering Katholieke Universiteit Leuven Kasteelpark Arenberg 44 bus 2450 B-3001 Heverlee Belgium e-mail: [email protected]

Chapter 16 A. K. Pickett Institute for Aircraft Design University of Stuttgart Germany e-mail: [email protected]

Chapter 17 E. Marklund* and L. E. Asp Swerea SICOMP AB Box 104 SE-43122 Mölndal Sweden e-mail: [email protected]; erik. [email protected]

J. Varna Div. Polymer Engineering Luleå University of Technology SE-97187 Luleå Sweden e-mail: [email protected]

Chapter 18 P. Middendorf* and C. Metzner EADS Deutschland GmbH Innovation Works

F. Dumont* and C. Weimer Production Techologies and Projects Laboratories, Materials and Processes Eurocopter Deutschland GmbH D-81663 Munich Germany e-mail: [email protected]; [email protected]

Chapter 20 B. Sköck-Hartmann* and T. Gries Institut für Textiltechnik (ITA) of RWTH Aachen University Otto-Blumenthal-Strasse 1 52074 Aachen Germany e-mail: Britta.Skoeck-Hartmann@ita. rwth-aachen.de; thomas.gries@ita. rwth-aachen.de.

Chapter 21 G. Adolphs and C. Skinner* OCV Technical Fabrics Chaussée de la Hulpe 166 1170 Brussels Belgium e-mail: Christopher.Skinner@ owenscorning.com; Georg.adolphs@ owenscorning.com

Chapter 22 P. J. Schubel University of Nottingham Faculty of Engineering University Park Nottingham NG7 2RD UK e-mail: [email protected]


Introduction

The subject of this book, non-crimp fabrics (NCF), is a textile engineer’s answer to a long-standing challenge faced by designers of composite parts: to combine a perfect placement of the reinforcing fibres with easy, inexpensive, automated manufacturing of the part. A part made using unidirectional (UD) tapes, placed by hand or by robot and consolidated in an autoclave, has ideal fibre placement and the best local mechanical properties due to the UD microstructure of the reinforcement. However, the manufacture of such parts is cumbersome and costly. On the other hand, an out-of-autoclave manufacturing process, for example vacuum-assisted resin transfer moulding (RTM) which uses woven laminates, is relatively cheap and takes advantage of easy handling of large sheets of the fabric. In this case, however, the local mechanical properties are affected, because the fibres deviate from their ideal directions due to the crimp (inherent to the woven fabric) and because of the necessary presence of the second fibre system, lying transverse to the direction of the design loads. Hence the challenge to create a reinforcement which would combine UD fibres with integrity, ease of handling and drape of textile fabrics. There are different ways to create such a non-crimp textile structure, which are reviewed in Chapter 1 of this book. These include quasi-UD woven fabrics, noncrimp and non-interlaced three-dimensional weaving, weft- and warp-knitting of UD plies and adhesive bonding of the plies. However, the rest of the book is dedicated to the most widely used type of NCF – multiaxial multiply warp knitted fabrics. The impressive examples of applications of composites reinforced by such NCFs include: a floor pan of a car, which weighs half was much as its steel prototype (carbon fibre NCF); a six-metre diameter pressure bulkhead of an A380 aircraft (also carbon fibre NCF) and a sixty-metre-long blade of a wind turbine (glass fibre NCF). This book presents a comprehensive overview of all the aspects of NCF usage as composite reinforcement – manufacturing of NCF in the textile industry, manufacturing of composites with NCF reinforcements and the mechanical properties of NCF composites and their applications. The chapters are rich in factual material, including test results for the most popular types of carbon and xvi © Woodhead Publishing Limited, 2011

Introduction

xvii

glass NCF and their composites, which makes the book a useful reference source. The book can also serve as a textbook for courses on NCF composites in an advanced study programme. Part I, ‘Manufacturing of non-crimp fabrics’ starts with an overview of types of NCF and production methods (Chapter 1, A. Schnabel and T. Gries), which is supported by the discussion of available standardisation of NCF in Chapter 2 (F. Kruse and T. Gries). NCF laminates, with plies in NCF layers stitched (warpknitted) with a thin polyester yarn with linear density of few tex, can be further stitched together with a thick strong glass, aramid or carbon thread, which will provide delamination resistance for the composite. The technology of such ‘structural stitching’ is described in Chapter 3 (P. Mitschang). The ideal UD placement of fibres in the plies of NCF is distorted by the needles and yarns during warp-knitting process. These distortions create an intricate pattern in the internal geometry of fibre placement and free spaces (which become resin-rich zones in the composite), as described in Chapter 4 (S. V. Lomov). As the fibre distortions define the significance of knock-down factors of the mechanical properties of NCF composites in comparison with their UD laminate counterparts, the characterisation and control of these defects is of paramount importance for quality control. An automated system for quality control is described in Chapter 5 (M. Schneider). Part II, ‘Manufacturing of non-crimp fabric composites’ focuses on two crucial phenomena: deformability of NCF during draping on a three-dimensional (3D) mould and resin flow through the fabric. Chapter 6 (S. V. Lomov) describes the resistance of NCF to shear, bi-axial tension and compression, as measured in laboratory tests. This knowledge is further advanced in Chapter 7 (P. Harrison, W-R. Yu and A. C. Long), which describes the behaviour of NCF during draping on a mould, based on mathematical models of the behaviour of a unit cell of NCF and the drape of NCF cloth. Discussion of resin flow through NCF starts with an overview of permeability measurements in Chapter 8 (R. Loendersloot), which also includes measurements of sheared and compressed laminates. Variability issues surrounding the permeability of NCF are covered in Chapter 9 (A. Endruweit and A. C. Long). The models of resin flow of NCF at unit cell level are introduced in Chapter 10 (B. Verleye, S. V. Lomov and D. Roose). These models allow prediction of the permeability of NCF, including sheared configurations, which can be used in macro-models of the part impregnation. Part III, ‘Properties of non-crimp fabric composites’ discusses the mechanical behaviour of NCF composites under different loading types and methods to model this behaviour and predict the mechanical properties. Chapter 11 (S. V. Lomov, T. Truong Chi and I. Verpoest) summarises the results of measurements of mechanical properties of NCF composites in tension and shear, and describes damage progression during a tensile test based on acoustic emission registration and X-ray post-mortem examination. Chapter 12 (L. E. Asp, J. Varna and


xviii

Introduction

E. Marklund) continues with a detailed microscopy examination of damage to NCF composites under tension, compression and impact loading. Fatigue behaviour of NCF composites is studied in Chapter 13 (K. Vallons), and mechanical properties of structurally stitched NCF composites in Chapter 14 (N. Himmel). All these studies have a common focus: to reveal and understand how distortions of the UD fibrous plies, introduced by the non-structural and structural stitching, influence the mechanical behaviour of the composite. This understanding helps to establish design limits for NCF composite part and to determine the knock-down factors for the mechanical properties in comparison with the properties of UD laminates, which can be predicted with well-known methods. Because of the complex internal geometry of NCF, predicting the mechanical behaviour of its composites is not that straightforward. Chapter 15 (D. S. Ivanov, S. V. Lomov and I. Verpoest) introduces meso-level (unit cell) finite element (FE) models which allow prediction of elastic response, damage initiation and progression and strength of NCF composites. Chapter 16 (A. Pickett) describes FE modelling of NCF composite parts on macro-scale, which integrates models of forming and infusion during manufacturing and structural analysis of the consolidated part. More engineering-type models (semi-laminar analysis) are described in Chapter 17 (E. Marklund, J. Varna and L. E. Asp). Part IV, ‘Applications of non-crimp fabric composites’ describes the existing and prospective use of NCF composites in aeronautics (Chapter 18, P. Middendorf and C. Metzner, and Chapter 19, F. Dumont and C. Weimer), automotive (Chapter 20, B. Sköck-Hartmann and T. Gries) and wind energy (Chapter 21, G. Adolphs and C. Skinner) industries. The authors do not limit themselves to success stories, but also describe the requirements and limitations for using NCF composites in their respective fields. This part finishes with the important issue of cost analysis of using NCF composites in engineering applications, in Chapter 22 (P. Schubel). The book summarises the results of research and developments performed mainly in the last ten years. During this time, I have worked in the Composite Materials Group (CMG) (Department MTM, Katholieke Universiteit Leuven). The leader of CMG, Professor Ignaas Verpoest, introduced me more than ten years ago to a fascinating world of textile composites. I acknowledge with gratitude his influence, leadership, scientific inspiration and – most of all – friendship. In wider terms, the research in the field of NCF was for myself an interesting and inspiring experience of being a part of a Europe-wide ‘NCF composites community’, spanning different ‘walks’ of science and engineering – textile and composites engineers and manufacturers, designers, experimentalists, university professors, software developers – and combining so many different application fields at the cutting edge of development of modern technologies such as aeronautic, automotive and energy. Woodhead Publishing undertakes continuous efforts in creating a comprehensive library of books on textile and composites science and technology. The present book is a part of this library, and I am grateful to the publisher for the opportunity


Introduction

xix

to edit it and to gather together a group of distinguished authors – experts in the field. Special thanks are due to Professor. Andrew Long, who has taken the role of editor for the chapters written by myself, and to the Woodhead staff – Adam Hooper, Bonnie Drury and Nell Holden, who helped in putting the book together. Stepan Lomov Leuven


1 Production of non-crimp fabrics for composites A. SCHNABEL and T. GRIES, Institut für Textiltechnik (ITA) of RWTH Aachen University, Germany

Abstract: For the manufacturing of non-crimp fabrics there is a wide range of production technologies. The focus in this chapter is on the production of warp-knitted non-crimp fabrics. The production process of coursewise and non-coursewise biaxial and multiaxial warp-knitted NCF is described in detail and the production of non-crimp fabrics by means of weft knitting with weft insertion and specially adapted weaving processes is explained. Other processes are shown to produce non-crimp fabrics made of tapes and threads by means of resins or adhesives. The different technologies are compared and evaluated. An outlook on actual and future research topics and developments concludes this chapter. Key words: production of non-crimp fabric (NCF), warp-knitted NCF, weft-knitted NCF, non-crimp woven fabric, fixation by adhesion.

1.1

Introduction

The chapter ‘Production of non-crimp fabrics, for composites’ comprises a short introduction to non-crimp fabric (NCF), an overview of production technologies and the produced fabrics, a comparison of production technologies, current trends and an outlook on the future. Non-crimp fabrics are defined as drawn parallel oriented layers of reinforcing threads or tows, which are positioned by means of an additional fixation material. Figure 1.1 gives an overview of different NCF structures. In technical literature, there is a wide range of terms for the production technologies for different kinds of fabrics. Furthermore, no uniform designation of thread systems is used. Therefore, at the beginning of each section, the terms used are introduced and, for clarity, throughout the chapter the terms ‘thread’ and ‘fibre’ will be used for reinforcement systems and ‘yarn’ for auxiliary systems. The definition of Roye et al. (2005), is used for the expressions two-dimensional (2D) textile and three-dimensional (3D) textile. • •

A textile is defined as a 2D structure if it does not extend in more than two directions, neither in yarn architecture nor in textile architecture. A textile is defined as a 3D structure if its yarn architecture and/or its textile architecture extends in three directions, regardless of whether it is made in one step or in a multiple-step process.

A cornerstone for the production of NCF was set in 1949 with patent number DD000000008194A, granted to Heinrich Mauersberger. The patent describes a 3 © Woodhead Publishing Limited, 2011

4


1.1 Overview of different non-crimp fabrics (ITA).

novel textile material and the associated production method. The basic idea is that chain-stitch seams are used for the production of textile fabrics by interlinking loose filling threads or drawn parallel weft threads. Intersecting weft threads are routed with a guide rail and connected with chain-stitch seams. Threads that are fed in process direction to the stitching unit can be fixed via a ‘zig-zag’ chain stitch. The position of the needle puncture should be between two weft threads (Mauersberger, 1954). NCF can also be produced with coursewise warp-knitting technology, weftknitting technology and specially adapted weaving processes. Besides the above-



5

mentioned methods, incoherent reinforcing fibre layers are joined and positioned by being pre-impregnated with resin or by fixation with adhesives. Adhesives for the joining of non-crimp fabrics are used in the form of fluid, powder, granulate or non-woven hotmelt.

1.2

Warp-knitted non-crimp fabric (NCF)

Knitting processes with loop formation in production direction are called warpknitted fabrics. The compound needles are assembled on a continuous needle bar and moved together during the loop formation. Due to the production process, warp-knitted fabrics are created with several yarn systems (Anon., 1969). In warp-knitted NCFs the loop formation is used to bind reinforcing layers together. The machine technology is very productive compared to other technologies. Warp-knitted NCFs are very flexible in respect to layer setup and fibre orientation, but they are limited to a constant width and area weight. There is coursewise and non-coursewise fixation of the reinforcing threads. In a machine with coursewise weft insertion, every warp and weft thread is bound with a single knitting loop. Compared to other technologies, the threads remain undisturbed. The stitch length can be defined in the machine settings. The technology for coursewise biaxial and multiaxial NCF is called warp-knitting. In machines with a non-coursewise weft insertion, the stitch length is independent to the position of the thread. Therefore, threads can be damaged or deflected. There exist non-coursewise biaxial and multiaxial NCF. Non-coursewise multiaxial NCFs are called warp-knitted multiaxial layers (Verwirkte multiaxiale Gelege; WIMAG) or stitch-bonded fabrics (Nähgewirkte variable Gelege; NVG). These phrases were coined in the Federal Republic of Germany and in the former German Democratic Republic, respectively. The term ‘stitch-bonding’ is more appropriate to describe non-coursewise weft insertion technology. Nevertheless, in the following, the more common term ‘warp-knitting’ will be used for noncoursewise biaxial and multiaxial NCF (Weber and Weber, 2004; Wulfhorst, 1998). Table 1.1 shows the important properties of coursewise and non-coursewise fabrics and the relating production technologies. Table 1.1 Characteristics of coursewise and non-coursewise non-crimp fabric and the relating production technologies

Fibre damage Dislocation of the reinforcing threads Variability of the stitch length Complexity of the machine technology

Coursewise weft insertion

Non-coursewise weft insertion

− − + +

+ + + −

+ Higher/− Lower


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1.2.1 Biaxial warp-knitted NCF Fabric set-up Biaxial warp-knitted NCFs are made out of at least three thread systems. • • •

Pillar threads (0°). Weft threads (90°). Warp-knitting yarns.

The reinforcing threads are fed parallel (pillar threads) and perpendicular – respectively diagonal – (weft threads) to the process direction. Warp-knitting yarns are often manufactured from a thermoplastic, such as polyethylene or polyamide, and are used for the fixation of the intersection points of the pillar and weft threads. The yarn spacing between the pillar and weft threads can be adjusted depending on the application. Figure 1.2 shows a scheme of biaxial warp-knitted fabrics with coursewise (a) and non-coursewise (b) weft insertion and different yarn spacings. Unidirectional warp-knitted fabrics can be produced in principle with biaxial warp-knitting machines with weft insertion. Thereby, only weft threads are processed and positioned with warp-knitting yarns.

1.2 Biaxial warp-knitted non-crimp fabrics with coursewise (a) and non-coursewise (b) weft insertion (ITA).

Working principle The warp-knitting machine with biaxial weft insertion can be divided into three machine modules. • • •

Feeding module. Warp-knitting module. Take-up module.

The feeding module consists of a weft insertion system, which is continuously filling weft threads into the hooks or needles of two transport systems. There is one transport system on each side of the machine. The distance between the transport systems defines the width of the fabric. The transport system continuously supplies the loose fibre layers to the warp-knitting module. The pillar threads are



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1.3 Warp-knitting machine with biaxial weft insertion (ITA).

guided by the pillar thread sinkers and fed directly between the compound needles. The weft and pillar threads are fixed in the warp-knitting unit together, by means of warp-knitting yarns. Afterwards, the NCF is cut out of the transport chain and is wound onto the take-up module. Figure 1.3 shows the working principle and the essential functional features of a warp-knitting machine with biaxial weft insertion. Feeding module Weft carriage system Weft carriage systems are mounted on a portal, which is positioned above the transport systems of a warp-knitting machine with weft insertion (Fig. 1.4). The weft carriage system swings permanently between the two transport systems. Thus the weft carriage system take-off takes threads out of a stationary creel and supplies these threads to the transport systems. In the reversal points of the insertion device, the weft threads are pressed down mechanically. Subsequently, the threads lay between the hooks of a shogging rake and at the same time at the back of the weft lay-in units of the transport system. The shogging rake shifts laterally and the weft insertion starts to move in the other direction, whereby the threads are fixed in the weft lay-in units. As soon as the weft threads are fixed, the weft-insertion device moves to the other side of the machine and continues with the same procedure (Wunner, 1987). Parallel and cross-weft insertion can be realised with computer-controlled weft carriage systems (Mayer, 2007).


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1.4 Weft carriage system (ITA).

Weft thread transport system Transport chains are widely used as weft-thread transport systems in weft insertion machines. The ratio of the speed of the transport chain to the number of revolutions of the knitting elements determines the stitch length of the warp-knitting yarns. Weft thread transport chains of warp-knitting machines with biaxial weft insertion can be equipped with a wide range of different weft lay-in units. The weft lay-in units can be divided into hook and needle systems (Fig. 1.5), which are used for coursewise and non-coursewise weft insertion (LIBA, 2007c).

1.5 Hook (left), needle (middle) and pin-hook system (right) (ITA).

Hook systems are applied generally for coursewise weft insertion. Weft threads are endlessly filled into open transport hooks, which are closed by weft clamps automatically. The clamps fix the weft threads with an optimum tension and in their exact position during the warp-knitting process. Therefore, the weft threads are drawn parallel and no thread tension difference can occur (LIBA, 2007e). The thread density in the transport system is unequal to the thread density in the fabric. Open, as well as closed, structures can be produced. Closed structures are produced with a fully threaded hook system and an adapted ratio of the speed of the transport chain to the number of revolutions of the knitting elements. Open structures can be manufactured with partly and fully threaded hook systems and a corresponding speed of transport chain. In needle systems, the transport chain segments are equipped with needle hook leads (LIBA, 2007c). When the weft threads are laid down into the weft lay-in units, the needle hooks can penetrate and split the weft threads. Due to this system, the exact position of the threads cannot be guaranteed. Needle systems are used,



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therefore, for non-coursewise weft insertion. If many threads are supplied to the needle hooks, closed fabrics with a high density and an even distribution of weft threads can be produced. The pin-hook system is a further development of the needle system. Pins and hooks are arranged in two separate rows. The vertical pin row defines the gauge of the weft layers, whereas the horizontal hooks take up the tensile force of the threads. Therefore, the weft threads can be filled directly – without a shogging rake system – into the weft lay-in units (Wiedenhöft and Vettermann, 1999; Zeidler et al., 2005). The pin-hook system promises a higher quality (e.g. a reduced number of gaps between the weft threads) of the finished textile, but also a higher percentage of blends. Creel Rovings – endless, drawn, twist-free filament bundles – from cheeses and bobbins are fed from creels. These creels are equipped with thread brakes or compensation thread tensioners to regulate the thread tension. Integrated thread breakage and tensioned thread inspection displays show fractured and tensioned threads optically. Bobbin creels for weft insertion have to be adapted, because of the intermittent thread consumption and the brittle fibre material. Bobbin creels are equipped with individual bobbin drives and buffer storages to achieve a constant tension and take-off speed (Fig. 1.6). These creels can also be used to spread fibre tows with up to 48 000 filaments in warp-knitting machines with multiaxial weft insertion. There are also cheese creels with compensating thread tensioners, which are used for biaxial and multiaxial weft insertion (Hoersting and Wienands, 1999; LIBA, 2004; Mayer, 2009c).

1.6 Bobbin creels (left and middle) and cheese creel (right) with compensating thread tensioner (ITA).


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Machine equipment Additional equipment for warp-knitting machines with biaxial weft insertion are conveyors, fibre choppers and fleece devices. The conveyor transports chopped fibres to the knitting elements, where fibre layers and chopped fibres are fixed together. Fleece devices are used for feeding of fleece rolls above or underneath the weft threads. Warp-knitting module In the warp-knitting module, the loose fibre layers are fixed together with knitting loops. The motions of the knitting elements (Fig. 1.7) are generated with eccentric gears and corresponding actuating levers. Each knitting element has its own gear. The eccentric gears are driven by a three-phase asynchronous motor with servo converter, which is controlled electronically (LIBA, 2007e).

1.7 Knitting elements (coursewise weft insertion) and walking needle concept (LIBA, 2007e).

Warp-knitting machines with biaxial weft insertion are produced mainly with working widths from 102 to 245 inches and gauges from 3.5 to 24. A gauge is defined as the number of needles per inch (25.4 mm). Loop formation process The loop formation process is divided into seven steps (Fig. 1.8), which are carried out continuously and represent one revolution of the main shaft (Mayer, 2009e; Weber and Weber, 2004). 1. In the first step of the loop formation process, the compound needles and closures, respectively slides, are in their lowest position. The heads of the compound needles are covered from the closures, the guide bars are in their foremost position and the underlapping of the guide bars is carried out.



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1.8 Loop formation process (ITA). See text for further explanation.

2. In the second step, the compound needles stroke upward, whereas the closures stay in their lowest position and the pillar thread sinkers fix the vertical position of the fabric. The knit loops slide out of the needle heads onto the needle shafts and the guide bars complete the underlapping motion. 3. In the third step, the compound needles reach their topmost position, the closures start to stroke upwards and the guide bars begin to swing past the compound needles. 4. In the fourth step, the compound needles and closures stay in their topmost position. The closures are still inside the grooves of the compound needles. The guide bars reach their sternmost position, begin to overlap and start to swing backwards. 5. In the fifth step, the guide bars swing past the compound needles and closures, which are still in their topmost position. The guide bars lay the warp-knitting yarns into the hooks of the compound needles. 6. In step six, the guide bars swing into their foremost position. The compound needles stroke faster downwards than the closures. The closures emerge out of the grooves and begin to cover the heads of the needles. The previous knit loops start to slide upwards from the needle shafts. 7. In the seventh step, the compound needles and the closures emerge between the knock-over sinker. The knit loop slides over the covert compound needles and is cast off. Thereby the warp-knitting yarns in the needle heads are pulled through the casted loops and complete the loop formation process. Walking needle The puncture of the fabric through the compound needles and the simultaneous movement of the fabric can lead to damage and deflection of the reinforcing threads. In the walking needle system, an additional horizontal movement – in the direction of production – during the vertical stroke, is carried out in order to reduce the negative influence of the needles. The degree of horizontal needle movement can be adjusted manually with an adapted actuating lever (LIBA, 2007c).


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Weft thread sinkers Weft thread sinkers as well as weft inserters allow a precise positioning and fixation of weft threads in coursewise weft insertion systems. The weft thread sinkers place the weft thread closest to the knitting elements on the back of the compound needles. The weft threads are kept in this position until they are fixed with warp-knitting yarns. One of the limiting factors for the working speed of biaxial warp-knitting machines is the weft insertion frequency. Therefore, special thread-forward devices were developed. They accelerate the weft thread next to the warp-knitting elements and therefore increase the distance to the following weft thread. The accelerated weft thread can then be fixed without being constrained by the previous, or the following, weft thread. Thereby a reduced gauge of the weft lay-in units can be realised. Hence, more weft threads can be fed at any one time and, furthermore, the amount of the weft threads in the transport chain is reduced (Wunner, 1974; Wunner, 2009; Weiland, 1988). Yarn let-off Yarn let-off systems are generally classified in positive and negative systems. In negative systems, the needles pull the required amount of yarn from warp beams, section warp beams or bobbins. The yarn tension is controlled with yarn-tension devices or yarn brakes, which limit the maximum working speed. In positive systems, the required yarn length is provided from usually electromechanically driven warp beams. Furthermore, electronically controlled yarn let-off systems with a constant or a variable yarn intake are used. For the adjusted supply of the pillar threads, electromechanically driven delivery rolls are used (Wuensch, 2008). Stitch types There exist different stitch types in knitting patterns to join the loose fibre layers together. The stitch types are predetermined by the scaling of the underlap of the guide bar, which is driven mainly by pattern discs. The most common stitch types are pillar, tricot and plain (Fig. 1.9). The stitch type and the stitch length affect the drapability of the fabric. The drapability is defined as the spherical deformability of flat textile material without structural folds, which is equivalent to the adaptation of flat textile material onto curved 3D surfaces. A larger underlap and a greater stitch length of the warp-knitting yarn increase the formability and at the same time complicate the handling of the material (Hanisch et al., 2007; Hufenbach, 2007). Take-up module The take-up module is located towards the warp-knitting module and consists of a weft thread cutting device, a suction device, a fabric take-off and a fabric wind-up.



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1.9 Stitch types – pillar (left), tricot (middle) and plain (right) (ProCad Warpknit 3D ITA).

The cutting device and vacuum cleaner The weft thread cutting device detaches the weft thread ends from the transport chain after the warp-knitting elements. Common cutting devices are thermal systems, hard metal scissors and motor-driven diamond-disc blades. The weft thread blend in the transport chain is brushed out and removed with a vacuum cleaner. Fabric take-off For the fabric take-off, mechanically or electronically controlled systems with two to three rollers are used, which provide an appropriate tension in the fabric. In mechanical roller systems, the take-up speed can be adapted by changing the transmission ratio of the gearbox. Electronically controlled roller systems offer the possibility to adapt the take-up speed as input into the machine’s operation (Wuensch, 2008). Fabric wind-up Two different kinds of batching devices – radially or axially driven – are applied in warp-knitting machines with biaxial weft insertion. They are selected depending on the material. Axially driven wind-up systems have a centre drive with a slipclutch. The wind-up speed can be controlled with skipping rollers. Radially driven wind-up systems are constantly driven at the circumference by friction rollers. They have two operating modes: speed and instantaneously regulated (LIBA, 2005; Mayer, 2007, 2009a). Machine operation The machine operating system is housed in a dust-resistant and air-conditioned control cabinet to protect it from fluff and mechanical damage. The central machine operating system controls all functions of the machine, such as production


14


speed and fabric take-off speed. The operating system is equipped with a counterlayer calculation including automatic optimizing and a printer to keep records of product and fault protocols. The operating panel shows production parameters, malfunctions and indicates necessary maintenance work. Furthermore, the operating system is linked to an external customer network by an ethernet interface. External remote diagnostics via modem allow machine diagnostic and customer support for rapid problem-solving through the machine manufacturer (Petrenz, 2009; Mayer, 2009b; Anon, 2010a).

1.2.2 Multiaxial warp-knitted NCF Multiaxial warp-knitting technologies for coursewise and non-coursewise weft insertion (Fig. 1.10) have been developed (Arnold et al., 2000; LIBA, 2007d; Parekh, 1989). Multiaxial warp-knitted NCF with coursewise weft insertion has not yet become generally accepted in practice. Therefore, only the most important characteristics of the fabric and the production technology are given in this chapter. Multiaxial warp-knitted NCF with non-coursewise weft insertion is produced with a machine technology that is similar to the warp-knitting technology with biaxial weft insertion and therefore only the main differences are explained in this chapter. The productivity of the machine depends mainly on the number of stitches per minute and on the stitch length of the warp-knitting module as well as the frequency and the width of the weft insertion (Petrenz, 2009). Warp-knitting with multiaxial weft insertion is one of the most commonly used production technologies for the manufacturing of multiaxial NCF. Fabric set-up Multiaxial warp-knitted NCF with coursewise weft insertion is made of up to four reinforcing fibre layers consisting of diagonal weft threads (e.g. 45°), weft threads (90°) and warp threads (0°). They are fixed using warp-knitting yarns (Anon, 1986).

1.10 Multiaxial warp-knitted non-crimp fabric with coursewise (a) and non-coursewise (b) weft insertion (ITA).



15

Multiaxial warp-knitted NCF with non-coursewise weft insertion consist of a current maximum of seven parallel layers of rovings or spread fibre tows. The orientation of the single fibre layers can be freely adjusted to between −20° and +20° relative to the production direction (angle specification analogous to EN13473-1). On the top side of the fabric, an additional layer at 0° can be attached. The introduction of two surface fabrics, for example non-wovens, is also possible (Fig. 1.11). The mass per unit area, the structure – closed or open – of the fabric, the material as well as the thread count of each layer can be varied individually for each layer. The single fibre layers are fixed together with a warp yarn (LIBA, 2007d; Mayer, 2009d).

1.11 Schematic set-up of a multiaxial warp-knitted non-crimp fabric with non-coursewise weft insertion (LIBA, 2007d).

Working principle In coursewise weft insertion machines, the knitting unit, a beam with multiple pillar threads (0°), a transport system for weft insertion (90°) and a take-up unit are mounted on a large turntable, which rotates around its own vertical axis. Stationary beams or creels supply reinforcing threads for the diagonal weft insertion to the rotating knitting machine (Fig. 1.12). Up to two diagonal thread systems can be fed. Because of the superposition of the stationary and the rotating systems, the threads are laid diagonally across the width of the fabric (Parekh, 1989). The working principle of non-coursewise weft insertion machines is comparable to that of biaxial warp-knitting machines. The standard machine configuration consists of three weft carriage systems, which are adjustable in small ranges or between −45° and +45°. The single fibre layers are filled in consecutive steps into the weft lay-in units of the transport system. The pillar threads made out of rovings have to be supplied directly between the compound needles to avoid shifting after deposition (Fig. 1.13). Fibre deflections (undulations) can lead to fabrics with lower quality and, therefore, to fabrics with reduced mechanical properties. Therefore, the pillar threads are fixed immediately together in the warp-knitting module by at least two knitting heads (Wienands et al., 2004).


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1.12 Coursewise multiaxial warp-knitting machine (top, ITA; bottom, Anon, 1986).

Several other approaches to producing multiaxial warp-knitted NCF with 0° layers at any position – between or on top of the other fibre layers – have been developed. In one process, a conventional fabric with a 0° layer on top is manufactured and afterwards merged with another fabric on a separate machine. To get a symmetrical NCF, the upper fabric has to be turned over. Threads in the production direction can also be fixed on any layer by coating them with glue or heating them up to their melting point. A fixation by means of adhesive is not necessary when spread and torsion-free fibre tows are fed (Friedrich, 2002; Wagner and Palmer, 1998; Anon, 2005).



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1.13 Non-coursewise multiaxial warp-knitting machine (top, LIBA, 2007d; bottom, Karl Mayer Textilmaschinenfabrik GmbH, 2010).

Feeding module Weft carriage system There exist two substantial weft insertion technologies in non-coursewise multiaxial warp-knitting machines. • •

Insertion of endless weft threads. Insertion of finite weft threads.

Weft carriage systems for the insertion of endless weft threads manipulate roving and small spread fibre tows (12k) made of carbon. These tows are less expensive than conventional carbon fibre rovings. A weft carriage system with a clamping and cutting device is used for the placement of the fibre tows.


18


1.14 Stationary (left) and mobile (right) weft insertion portal (ITA).

Closed NCF with an areal weight of at least 75 g/m2 can be produced (Bompard et al., 2005; Bittmann, 2006; Anon, 2002, 20056; LIBA, 2007b; Mayer, 2009f). There are stationary and mobile weft insertion portals (Fig. 1.14). In stationary systems, only the weft carriage systems are moveable. They are positioned on a linear guide of the weft insertion portals. In stationary systems, the orientation of the fibre layers is predetermined by the position and accordingly the angle of the weft insertion portal in respect to the direction of the process. The angle has to be adjusted to the ratio of working speed and weft insertion speed. The fibre angle can be changed mechanically within a predefined range (Naumann and Wilkens, 1986). In machines with mobile weft insertion portals, the weft carriage systems can move independently parallel and lateral to the process direction of the warpknitting machine. The orientation of the fibre layers result from the superposition of the transport system motion and the portal movement (Wunner, 1987; Hoersting et al., 2002). In stationary systems, the moving mass is lower and the carriage system can be guided more accurately, but they are less flexible compared to mobile systems. Weft thread transport system Transport chains with needle, pin-hook (q.v. 1.2.1 Biaxial warp-knitted NCF) and pin-pin systems are used for the production of multiaxial warp-knitted NCF, which are made out of endless weft threads. Finite weft threads are fixed and transported with needle fields or clamping systems in warp-knitting machines with multiaxial weft insertion (Fig. 1.15).

1.15 Pin-pin (left), needle-field (middle) and clamping system (right) (ITA).



19

The pin-pin system was developed for the processing of small fibre tows (30J) is usually better than the properties of NCF or of UD material, due to decreased areas of damage. The modification of liquid resin infusion materials with low- or no-fibre crimp, produces promising results by the insertion of inherently tough particles into the matrix system. The mainly thermoplastic-based particles, e.g., polyamide or polyethersulfone, can be inserted as a fleece, powder binder or thin yarn into the textile preform. These toughening agents modify the brittle interfaces of the


444


18.3 Residual compression strength and delaminated areas against impact energy.

composite material after the resin infusion process in which cracks occur during impact. The reduced areas of damage lead to increased residual strength following impact, as presented in Fig. 18.3. Besides the damage tolerance performance, which is more resin-related, further specific requirements for aeronautic applications with respect to NCF composites are: formability for high curvatures and low area/weight relationship for skin lay-ups. The formability of dry textiles is one of the interesting benefits of liquid moulding technology. Prefabricated textiles such as NCF and woven or braided materials can be draped into complex two dimensional curved moulds without any fibre crimp or folds which could affect mechanical performance. During draping, the dry textile, for example biaxial NCF, is deformed in a shear mode so that the reinforcement fibre orientation and area/weight relationship may be partly changed. These parameters can be simulated or measured and have to be taken into account during the design stage. The formability of NCF is affected by the stacking sequence, ply area/weight relationship, fibre type and the tension and stitching pattern of the consolidation stitching yarn. An inserted binder may be used to fix the textile preform into the default geometry. This binder may be inserted between each processed ply or as a preliminary in the textile. Preliminary binder insertion improves the stability of the textile preform, but decreases formability due to blocking the shear performance of the fibre plies. The complex draping process is performed manually, but full automation will be feasible in the near future. This will significantly reduce lead time and costs, so improving consistency and quality assurance. Further benefits can be achieved with a low area/weight relationship per ply. State of the art in NCF technology is about 130 g/m2 per C-fibre ply which gives a minimum laminate thickness of less than 1.0 mm (quasi-isotropic symmetrically


Aerospace applications of non-crimp fabric composites

445

stacked laminate at 60% fibre volume content). Weight savings can therefore be achieved through adapting laminate orientation and thickness.

18.3

Application examples

18.3.1 Airbus A380 rear pressure bulkhead The first application of a composite rear pressure bulkhead (RPB) in a commercial aircraft was on the Airbus A340–500/600. Whilst the conventional A340 concept was based on prepreg fabric, the next generation has been developed with textile technology using carbon NCF, which has been applied on the A380, in which it was used for one of the biggest aeronautic NCF composite parts. The pressure bulkhead is a load-bearing primary structure which separates the pressurised fuselage from the non-pressurised rear section (see Fig. 18.2). Due to the nature of the internal pressure load, it is designed as a membrane structure with integrated stiffeners. In addition to the pure structural requirements such as stiffness and strength, the design must also meet strict fire, smoke and toxicity specifications. The A380 RPB is produced at the Airbus plant in Stade, near Hamburg. The preform is made from multiaxial carbon fibre NCF supplied by Saertex. For preform integration and handling, a gantry sewing machine is used to join the dry fabrics by blind stitching, finally forming an eight-metre-wide carpet. This preform is draped over a positive mould and then laminated using the resin film infusion (RFI) process (Fig. 18.4). After an initial curing of the 3 mm thick basic laminate

18.4 Draping of the non-crimp frabric carpet in the Airbus A380 Rear Pressure Bulkhead production.


446


and the attachment of stringers, the part is finally cured in an autoclave. The finished bulkhead weighs about 240 kg and is 6.2 metres by 5.5 metres in size. Airbus, EADS Innovation Works, Saertex GmbH and KSL Keilmann GmbH cooperated closely on the research, development and production of the A380 pressure bulkhead (EADS, 2004).

18.3.2 Airbus A400M cargo door The rear cargo door of the pressurised fuselage of the new Airbus Military transport aircraft A400M, is within 7 × 4 metres of the dimensions of the A380 rear pressure bulkhead. It also consists largely of multiaxial carbon NCF with additional UD fabric for local reinforcements and skin lay-up. But in contrast to the RFI process of the RPB, the A400M cargo door is processed without an autoclave, using the EADS/Premium Aerotec patented vacuum-assisted process (VAP) infusion technology (Fig. 18.5). Completed layers are placed into the mould directly from the roll and reinforcement layers are cut by an NC cutter, then positioned using laser projection. The skin has 16 stringers on the inner surface which are infiltrated and cured in one shot, together with the skin lay-up. The fully integrated design saves around 3000 joint elements in the consequent assembly process. This reduces lead time and costs, together with a significant weight improvement (PAG, 2009). As well

18.5 Airbus A400M Cargo Door manufactured at Premium Aerotec, inside view.


Aerospace applications of non-crimp fabric composites

447

18.6 Airbus A400M Cargo Door, outside view.

as the stiffened skin, the frames and the central beam are made of NCF and UD layers for local reinforcement of the upper flange. These parts are manufactured in a female mould as the exterior dimensions are important in the assembly process (Fig. 18.6). The A400M cargo door is manufactured at Premium Aerotec site, Augsburg and received the JEC Innovation Award in 2009.

18.3.3 Further applications on sub-structure level Besides the large-scale structures described above, there are some additional aeronautic applications on the sub-structure level. For commercial aircraft, these are principally the Airbus A380 flap track CFRP parts such as diaphragms, side shells and straps which are manufactured with NCF/epoxy infusion resin in VAP technology by Premium Aerotec. For helicopter composite airframes and business jet primary structures, smaller components made of carbon NCF are already in production or in the preparation phase.

18.4

Future trends

In common with other branches of industry such as automotive or wind energy, the challenge in the application of composite materials in future aeronautic structures will consist mainly of cost reduction when compared with state-of-the-art


448


prepreg technology. The volume of production will have to increase to meet the demands of the next generation commercial aircraft programmes. NCFs in combination with a highly automated production line (cutting, handling, draping, performance fixation) have the potential to offer many advantages. As mentioned in Section 18.2., an important prerequisite for the increased application of this technology is the improvement of the damage tolerance behaviour of NCF/epoxy infusion resin systems. The insertion of thermoplastic particles into the textile preform is promising in this respect, but several issues must be taken into consideration when incorporating these materials into future aircraft structures. • • •

Toughening particles inserted into the textile raw material, e.g., as a powder binder, may reduce the formability due to the decreased textile shear performance of the C-fibre filaments. During the infusion process, potential washout or preliminary dissolution in the resin may occur. This is not acceptable as homogeneous material properties need to be ensured. Some thermoplastic toughening agents tend to absorb water. In combination with a decreased glass transition temperature, this may cause shortcomings in the laminate performance under hot/wet conditions.

Most of these issues can be addressed by selection of materials and improvement of the insertion approach, so as to generate high-impact resistant laminates with small delaminated areas which have high in-plane compression properties. This results in high residual strength even under hot/wet conditions. Promising, stateof-the-art toughening agents offer the possibility of inserting high-temperature melting polyamide fleece between each C-fibre ply. Performance regarding the delaminated area and residual strength is presented in Plate XII and Fig. 18.3.

18.5

References

Airbus Material Dialogue, Bremen, 2006. EADS Corporate Media, International Air Show ILA, Berlin, 2004. Gay D, Hoa S V (2007), Composite materials: design and application, 2nd ed, Boca Raton, CRC Press. Jones R M (1998), Mechanics of Composite Materials, 2nd ed, New York & London, Brunner-Routledge. Petiot C (2007), Design of High-performance Composite Structures – State-of-the-Art, and Challenges, in Guedra-Degeorges D & Ladeveze P (eds), Course on Emerging Techniques for Damage Prediction and Failure Analysis of Laminated Composite Structures, Toulouse, Cepadues Editions. Premium Aerotec, Premium Aerotec wins JEC 2009 Innovation Award, Press release, 2009.


Plate XI Parameters for the delamination interface model for materials NCF/LY3505 (* estimated) (Chapter 16).

Plate XII C-scans of impacted non-crimp fabric and prepreg specimens (30J) (Chapter 18).

Plate XIII Typical blade layout IEC class II 40m blade detailing the laminate constructions based on non-crimp fabric reinforcement materials (Chapter 21).


19 Non-crimp fabric: preforming analysis for helicopter applications F. DUMONT and C. WEIMER, Eurocopter Deutschland GmbH, Germany

Abstract: This chapter deals with the preform manufacturing stage of non-crimp fabric (NCF) reinforced composite. An introduction is given to the concept of tailored reinforcement (TR), together with an overview of the forming techniques for NCF reinforcement with respect to quality. The main deformation modes of dry NCFs are presented. Finally, a description of the main defects occurring during preforming is given. Key words: non-crimp fabric, forming, preforms, deformation modes, defects.

19.1

Introduction

Characterised by high development efforts and medium production volumes, the aeronautical industry will ensure its competitiveness with an improved time and cost to market. Efficient lightweight design of composite parts will become a key factor to enhance the mechanical performance, to ensure weight saving and to achieve cost and fuel efficiency for aircraft and helicopters, it also makes an important contribution to facing rising environmental challenges. Carbon fibre reinforced polymer composites (CFRP) are state-of-the-art in high-performance helicopter structures such as airframes, empennage, or rotor blades. Eurocopter's TIGER and NH90 structures largely consist of CFRP materials (Weimer and Dumont, 2009). Currently, the majority of structural parts consist of prepreg materials made of hand lay-up and cured in autoclave. Cost drivers are hand-work, autoclave usage and quality control respective inspection. The future success of new helicopter programmes strongly depends on developing costefficient manufacturing methods as well as on optimising concurrent engineering processes for complex CFRP parts. A promising process type is liquid composites moulding (LCM) based on preform resin impregnation. Processes such as resin transfer moulding (RTM), or vacuum-assisted process (VAP) allow for automation, out-of-autoclave curing and online quality management (OQM). The quality of the part is firstly determined by the preform preparation.

19.2

Preform techniques for non-crimp fabrics (NCFs)

The use of uni- or bidirectional prepreg material is associated with high labour and material costs. The tackiness of the prepreg layers impedes machine forming 449 © Woodhead Publishing Limited, 2011

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and thus reduces the possibility of process automation. In addition, autoclave curing, which is mandatory for high-performance prepreg parts, is long and expensive (Åström, 1997). With preforming and liquid resin infusion, faster cycle times and a higher degree of automation are achievable. Preforms are often manufactured from woven fabrics. The yarns of available woven fabrics are usually oriented in a 0° and 90° direction (Haberkern, 2006). The need for fibres with 45° orientation in most structural applications increases the material cut-off and impedes a continuous manufacturing process. Another drawback of woven fabrics is their reduced mechanical properties due to the nonlinearity of the tensile behaviour caused by the crimp of the fibres (Hamila and Boisse, 2007). A NCF is a stack of unidirectional (UD) plies combined by a stitching process. Those fabrics are available with varying fibre orientations, e.g. [0°/90°], [+/− 45°] or [+/− 60°]. This enables a continuous manufacturing of multilayered preforms. The UD character of the plies enhances the mechanical properties compared to woven fabrics. These advantages explain the use of NCF for preforms. On the other hand, the forming properties of NCF differ from woven fabrics due to the asymmetry of the layers and the influence of the stitch, and need to be specifically studied.

19.2.1 Technical principle The manufacturing of preforms applies the principle of tailored reinforcements (TR) which involves the use of bound NCFs.

19.2.2 Preform process chain Two-dimensional (2D) preforming starts with a continuous multi-layer stacking sequence lay-up which is considered as a basic module for specific designs. Thanks to an automated lay-up machine, manufacturing of design-optimised lay-up packages becomes possible with different kinds of semi-finished products. The device is presented in Fig. 19.1. If required, a stitching step is carried out to achieve 2.5D semi-finished goods (so-called Intermediate Preforms, IP) with variation in thickness. As mentioned earlier, an alternative is the heating activation of the thermoplastic binder product. The lay-up plane is linked to a cutter machine which cuts the IP contours off, creating separated semi-products. Those semiproducts are then shaped during a forming step described in detail later. After the forming stage, the tailored reinforcements become sub-preforms (SP). Finally, 3DSP assembly is carried out again by stitching or by a new binder activation. The process concludes with a compaction step and a net-shape cutting. Fig. 19.2 illustrates this process chain for preforming.


Preforming analysis for helicopter applications

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19.1 Automated lay-up machine.

19.2 Non-crimp fabric preform process chain with quality gates (QG).

19.2.3 Tailored reinforcements Tailored reinforcements are semi-finished goods based on lay-up packages fixed together. The principles of lock stitch 2D automatic sewing machines have been introduced in Chapter 3. Additional descriptions have been given by Beier et al. (2007). The use of tailored reinforcement reduces the number of parts to be handled


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and makes possible the use of net-shape processing. On top of that, an integrated online quality assurance becomes possible (Dumont and Goettinger, 2009).

19.2.4 Types of forming methods A forming methodology is defined by the combination of a forming device and process parameters. It has a significant influence on the draping results (Long, 2007). The position, order and magnitude of the draping force application all contribute to the draping result (Tucker, 1997). The representations of these acting forces are made through the use of parameters such as draping force, tool friction, diaphragm properties, tooling displacement speed or forming vacuum level. The varying draping force and direction during manual draping disqualify the hand lay-up process as a suitable and reproducible preforming process. The automated forming processes described here are potential candidates to be embedded at an industrial level. Figures 19.3 to 19.5 show representations of the process principles. The first promising process is the single diaphragm forming, which combines the advantages of manufacturing reproducibility with a flexible formed shape capability. As depicted in Fig. 19.3, the tailored reinforcement is positioned between the tool's upper surface and a silicon membrane. A vacuum is set up between the base surface and the diaphragm, which deforms until a uniform pressure is applied on the upper surface of the tool. The reinforcement then conforms to this target shape. Heating can thus be applied in order to activate the binder solidification before demoulding the sub-preform. A second selected forming process is the drape forming (also known as stamping or match mould forming) where the tailored reinforcement is placed between two complementary hard tools, the male and female dies. A representation is given on Fig. 19.4. The forming of tailored reinforcements with drape forming has been revealed to be possible without additional restraint. The upper tool is closed and the preform is clamped before handling to the final preform. A third process has eventually awoken interest at an industrial level, despite its relative complexity: the stretch

19.3 Example of diaphragm forming for non-crimp fabric tailored reinforcements.



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19.4 Example of drape forming (or stamping) for non-crimp fabric tailored reinforcements.

19.5 Example of stretch forming for non-crimp fabric tailored reinforcements.

forming process (or deep-drawing). Largely used for metallic materials (Rohleder et al., 2002), the process is based on plug and ring forming (without female die) and characterised by additional boundary conditions introduced by blankholders (friction plate or springs). It is described in Fig. 19.5.

19.2.5 Final preform The sub-preforms (SP) are assembled to obtain the final preform. This near-net final preform will be put on the mould, compacted and then impregnated with resin.


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The binding of many layers together allows for a net-shape preforming (with variations in thickness, for example) and a better reproducibility. As depicted in Chapter 3, sewing is a common means of preform binding and assembly. Nowadays, new tackifying products have emerged that give reliable alternatives to ensure the stiffness for preform handling during manufacturing. Available as flakes or powder, they could be easily integrated in the preforming process. They contain a thermoplastic component fraction which is activated through heating. The heated activation time potentially slows down the manufacturing cycle time and may represent a drawback. Automation is again at this stage a major aspect. Basically, two different types of assembly can be distinguished, alike to the other preforming steps. Sewing robots have been developed especially for structural stitching in 3D. They can be flexibly equipped with different stitching heads (see Chapter 3). An alternative is an in situ activation of a binder material.

19.3

Main NCF deformation mechanism observed during preforming

For an extensive bibliographical study and complete definition of the deformability of the NCF material, one can refer to Chapter 6. This section will be focused on phenomenological descriptions used to define the global and local quality parameters of an NCF preform and to quantify their conformity thresholds. Table 19.1 illustrates the deformation described hereafter. Due to the low coefficient of thermal expansion of carbon fibres at the processing temperatures, the thermal deformation modes were disregarded as a possible mode of deformation in this approach. The main mode of mechanical deformation in NCF is the in-plane shear. Similar to the woven fabrics the planar shear is defined as a rotation of a yarn of one direction relative to the yarn of the other direction. Contrary to woven architectures, the rotation point is not the crossover anymore, but another reference point like the stitched point. High shear deformation angles can be achieved before the fabric starts locking, which is a sign of better drapability of the NCF-reinforcement. When extended to the macro level, a complete UD layer of the reinforcement shears (rotates) relatively to the other. The denomination is then intra-ply shear. Inter-fibre slip occurs when a fibre starts sliding through the fabric. Due to stitch looseness, the possibility exists for individual yarns to slide locally, relative to the parallel yarns (pull-out or fan effect), or to the ones from the other direction (nesting effect). Extension of this phenomenon is possible, creating subsequent an intra-ply slip. In this case, an entire zone of UD fibres moves relative to the other UD fibres, creating a planar shift. During the forming step, tension forces act in the fibre direction due to the friction and restrain contacts. This results in an elongation of the fibres. Until now fibre breakage was not as yet observed in industrial preforms.



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Table 19.1 Classification of deformation mechanisms during non-crimp fabric preforming Deformation mode

Level

Representation

In-plane shear

Meso

No

Intra-ply shear

Macro

Yes

Inter-fibre slip

Meso

Yes

Intra-ply slip

Macro

Yes

Fibre buckling

Meso/macro

Meso: yes Macro: no

Fibre extension

Meso

No

Fibre/ply compaction

Meso/macro

No

Fibre/ply bending

Meso/macro

No

Stitch stretching/ compaction

Meso

Yes


Non-crimp fabric specific

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19.6 Deformations of stitch yarns leading to loss of contact between stitch yarn and non-crimp fabric reinforcement itself.

During in-plane shear and intra-ply shear, the fibres are laterally compressed, leading to a mesoscopical reorganisation of the reinforcement. This effect stops when the planar shear locking angle is reached and wrinkles appear. Out-of-plane bending of fibres and reinforcement is of utmost importance during the forming stage of textile reinforcement as focused in Boisse et al. (2010). Two stitch deformation modes have been observed during preforming and deal with stretching and compaction. The deformations of fibres bundles implied by stitch yarn stretching have been depicted by Loendersloot (2005). Stitch compaction results from a lateral fibre compaction leading to loss of contact between stitch yarn and reinforcement itself, as depicted in Fig. 19.6.

19.4

Preforming defect analysis

During the intensive experimentation campaigns conducted on preforming for helicopter parts by Eurocopter, five NCF-specific defects have been identified (Dumont, Goettinger 2008). Contrary to the material production defects depicted through the quality testing method illustrated in the Chapter 5, the defects presented here are related to the forming stage and are observed during the preforming of the parts. Figure 19.7 shows local views of test preforms, illustrating the observed local flaws on each face. Due to the asymmetry of the layers and the influence of the stitch, the two sides of the bidirectional NCF reinforcement react differently and



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19.7 Terminology of defects observed on non-crimp fabric-preforms.

have to be presented separately. The following defect descriptions are complementary to Chapter 6, where mechanical deformability is extensively presented. The first potential concern deals with undulation of the fibres, accompanied with planar lateral compression of counter layer fibres and as such the space between those fibres decreases. This in-plane buckling (tagged as IB) is possibly comparable to the out-of-plane wrinkling often observed in draped woven fabrics. However, this extensive deformation occurs in the absence of outof-plane deformation, as the forming technique (described in Section 19.2.4.) produces a compression force on the reinforcement and impedes greatly the


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19.8 Limit fibre path (in white) of a preform on a helicopter frame.

wrinkling formation. This buckling is located on the outer side of a curved U-profile where the main radius decreases. Secondly, structure decomposition (SD) may be observed. It is due to a strong gradient in the path length of adjacent fibres, implying the local destruction of the NCF structure. This case is to be seen on a curved U-shape profile when one fibre remains complete (depicted as the limit fibre) and its adjacent fibre has been cut (conforming to the flattening contour). This implies a strong discrepancy of path length between the limit fibre and its neighbour. The limit fibre is showed in Fig. 19.8. The defect depicted as ‘compaction and stretch’ (C&S) is a combination of a lateral compaction of one fibre direction and stretch of the counter-fibre direction. The localisation of this defect is possible on the inner side of a curved U-profile where the main radius increases. In this extension it designates the opposite deformation of the fibre buckling described above (defect IB). Another potential flaw is a UD-ply slip relative to each other, and is denoted as intra-ply slip (IPS). Caused by the difference of fibre path lengths in each direction on a curved profile, the defect appears on the outer side of a curved profile where one fibre direction is orientated radial to the main curvature. It is noted that IPS arises often in combination with the SD defect. The last identified flaw is the presence of an opening or void (VO) on one face of the NCF reinforcement. Parallel fibres do not remain parallel locally, as in-plane forces act perpendicular to the fibre and cause an opening between adjacent yarns. These in-plane forces could be created during the reinforcement manufacturing by the sewing threads, forming a so-called fisheye (see Chapter 5) or afterwards during the preforming. During the impregnation of the preform, these defects lead to local resin accumulation and local weaknesses.

19.5

Conclusion and future trends

In this chapter, an overview has been given on the preform manufacturing stages of NCF-reinforced composite. The complete preforming chain has been introduced and commented upon. Moreover, the concept of tailored reinforcement has been presented, together with an overview of the forming techniques for NCF-tailored reinforcement with respects to quality. The technology has proven industrial readiness for many aerospace applications. Table 19.2 gives an overview of © Woodhead Publishing Limited, 2011


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such applications and the main benefits achieved by applying NCF processing technologies. The main deformation modes of dry NCFs have been detailed. Finally, a description of the main possible defects occurring during preforming has been given.

Table 19.2 Applications and main benefits achieved by applying the preform processing technologies based on non-crimp fabrics Applications

Description

Floor cover plate – Automated 2D lay-up of cross-ply stack – In-mould forming – Minimal number of individual sub-preforms

Structural longeron – High process stability – In-mould forming – Minimal number of individual sub-preforms

Curved frame – Weight saving – Non-developable near net-shape – Minimal number of individual sub-preforms


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Some very complex shapes can be formed from composite sheets, while other simpler shapes cannot be formed without a strong tendency to develop defects. This is the case for most industrial parts, for which an optimised forming methodology and procedure have to be found. This goal is being pursued at industrial level by using manufacturing process simulations coupled with a series of tests at industrial level (Dumont, Weimer 2008). Applying those models at an early stage of the design chain remains challenging and will need a consequent resource investment, together with an improved coordination between the research centres dedicated to the material characterisation, the companies releasing software tools and the final users like composites manufacturing companies.

19.6

References

Åström BT (1997), ‘Manufacturing of Polymer Composites’, Chapman and Hall, 103–106. Beier U, Fischer F, Sandler J K W, Altstadt V, Weimer C, Buchs W (2007), ‘Mechanical Performance of Carbon Fibre-Reinforced Composites Based on Stitched Preforms’, Composites Part A, 38, 1655–1663. Boisse P, Hamila N, Vidal-Salle E, Dumont F (2010), ‘Simulation of wrinkling during textile composite reinforcement forming. Influence of tensile, in plane shear and bending stiffnesses’, Composites Science and Technology (in press). Dumont F, Weimer C, Soulat S, Launay J, Chatel S, Maison-Le-Poec S (2008), The 11th International Conference on Material Forming ESAFORM, 23–25 April 2008, INSA, Lyon, France. Dumont F, Goettinger M, Weimer C (2008), ‘Analysis of NCF-preforms for helicopter composites parts’, The 9th International Conference on Textile Composites Texcomp, 13–15 October 2008, University of Delaware, Newark, USA. Dumont F, Goettinger M, Weimer C (2009), ‘Eurocopter Preform Analysis System’, ESAFORM Industrial Prize Award 2009, The 12th International Conference on Material Forming ESAFORM, 27–29 April 2009, University of Twente, Enschede, The Netherlands. Haberkern H (2006), ‘Tailor-made reinforcements’, Reinforced Plastics, 50, 4, 28–33. Hamila N, Boisse P (2007), ‘A Meso–Macro Three Node Finite Element for Draping of Textile Composite Preforms’, Applied Composite Materials, 14, 235–250. Long A C (2007), Composite forming technologies, Cambridge, Woodhead Publishing Limited. Loendersloot R, Lomov SV, Akkerman R, Verpoest I (2005), ‘Carbon composites based on multiaxial multiply stitched preforms. Part V: geometry of sheared biaxial fabrics’, Composites Part A: Applied Science and Manufacturing, Volume 37, Issue 1, January 2006, Pages 103–113. Rohleder M, Roll K, Brosius A, Kleiner M (2002) ‘Investigation of Springback in Sheet Metal Forming Using Two Different Testing Methods’, International Journal of Forming Processes, (3/4), 347–360. Tucker CL (1997), ‘Forming of Advanced Composites’, in T. G. Gutowski (ed.), Advanced Composites Manufacturing, John Wiley & Sons Inc., 297–372. Weimer Ch., Dumont F (2009), ‘Manufacturing Process Simulation Tools for Faster Industrialisation of Composite Parts’, Sampe Europe Technical Conference & Exhibition SETEC 2009, Filton, UK, September 17–18th 2009.


20 Automotive applications of non-crimp fabric composites B. SKÖCK-HARTMANN and T. GRIES, Institut für Textiltecknik (ITA) of RWTH Aachen University, Germany

Abstract: After a brief introduction to the history of automobile construction, the trend towards lightweight construction not only with metals but also towards multi-material constructions is explained. At present, short fibre reinforced sheet moulding components (SMC) and bulk moulding components (BMC) components are the dominant composite materials in the automotive sector. Today the use of non-crimp fabrics (NCF) is limited to automobiles in the luxury segment. Following this some recent examples of NCF components are discussed. These components only find application in high-end cars. The reasons for NCF components not being used for the mass production of automobiles are explained. Future trends of the mass production of textiles for automobile applications are outlined. Innovations and market potentials are shown. Key words: tailored non-crimp fabric, tailored braid, automotive, single-step preforming, multi-step preforming.

20.1

Introduction

When the first cars were built in 1885, they consisted simply of a coach car and a combustion engine. Around 1900, the first moulded steel frames were used. As a reaction to the increasing demand for cars, in 1922, the first industrial press for sheet metals was used for the production of car body parts. Thus automobiles with a wooden frame and a body consisting of plywood and metal sheets could be produced. In the 1920s, Lancia made the most progress concerning car body work. First the Lancia Lamda was designed, incorporating a self-supporting body. On this basis, Kässbohrer developed a sports car with a single-part aluminum cast body. Already in the 1940s, Henry Ford was the first to use natural fibres, which had been soaked with plastics, in the construction of an automobile. These first fibres were soya and hemp. Unfortunately, Ford’s car stayed unique and all further efforts fell victim to World War II. Even then, the high potential for weight reduction of about 50% has been stated (Greulich, 2007). The development of modern high-performance fibre-reinforced composites began about 50 years ago, when glass fibre reinforced plastics (GFRP) were tested and used for structural components of military planes and gliders. In 1953, glass fibres arrived in the automotive industry. Amongst others, Chevrolet used them for their Corvette (Ehrenstein, 2006). One of the first European cars made from 461 © Woodhead Publishing Limited, 2011

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GFRP was a Lotus sports car from 1962 (Anon., 2009). Chevrolet started using frontends made of glass fibre mat thermoplastics (GMT) as a standard feature in the 1975 model Monza. The same year, Porsche introduced the first completely galvanised steel body. Carbon fibre monocoques had been introduced for Formula 1 cars in 1981 (Ehrenstein, 2006). Already at that time, manufacturers were striving for lightweight construction in automobiles. However, this was not achieved by using fibre reinforced composite materials, but through the use of tailored blanks and the construction of aluminum sheet metal bodies. Aluminum became more and more important in the automotive business, resulting in the aluminum space frame design, which was developed for the Audi A8 in 1994. Only towards the end of the 1990s, the potential of fibre-reinforced plastics for applications in the mass production of automobiles was investigated (Derks et al., 2007). As a result, automobile manufacturers started research on multi-material methods of construction in 2000. Thus the weight reduction can be increased and the applied material can be adapted exactly to specific demands. Multi-material methods of construction have also been the topic of an EU project called ‘Super Light Car’, which is shown in Fig. 20.1. The Super Light Car consists of aluminum (sheet metal as well as cast parts), magnesium, steel and fibre-reinforced plastics (Berger et al., 2009). Looking closely at recent methods of body construction, one can find numerous different materials. In automobile construction, a general trend towards the use of composite materials and multi-material designs is apparent. However, the employed composite materials are almost exclusively short fibre reinforced sheet moulding components (SMC) or bulk moulding components (BMC) parts (JEC, 2009). The use of continuous fibre reinforced plastics is limited to unidirectional (UD) prepregs, due to their good mechanical properties. Prepregs consist of fibres and resin. They can be set hard by applying pressure and raised temperatures, but this process requires a hot press or an autoclave. In today's automotive industry, applications of glass or carbon fibre prepregs only appear in luxury and sports cars

20.1 Super Light Car (Berger et al., 2009).



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(Feraboli et al., 2004; Schauerte et al., 2007). The established technologies for the production of such prepregs suffer from the amount of parts needed. Therefore, many steps of the production process are dominated by manual work. Since an automated production has not yet been developed, cycle times for prepreg manufacturing are very long and not suitable for mass production. Moreover, material costs are very high and the raw materials require special storage conditions. Therefore, prepregs are used for components only in small serial applications with 100 to 500 pieces per year, as in Formula 1 cars. A notable share of the body parts, the chassis, the monocoque and the wheel suspensions incorporate prepreg systems. The use of NCF in automotive engineering occurs in the field of preform technology. The process of preforming is understood as the production of near-net shape textile preforms. By soaking them with resin via resin infusion (RI) or resin transfer moulding (RTM), these preforms become finished products (Räcker, 1997). At present, NCFs are rarely used for automobile parts, due to the missing automated process chains. The textile fabrics and binders are draped manually. With the existing preforming technologies, preforms and components made of NCF can be manufactured in quantities up to 5000 pieces per year using the resin infusion process. This is why, as well as prepregs, NCF are only used in small series cars like luxury class or sports class vehicles. With the use of an automated preforming process and resin transfer moulding, it will be possible to produce up to 50 000 pieces per year with more simple geometries and a two-sided formwork in the process of consolidation. Nevertheless, for these technologies only very few examples are available on the market. At present, preforming also still requires many steps of manual work. Fabrics are draped manually in the forming tools and the application of the binder to fix the single fabric layers is also a manual operation. The exploitation of new applications of continuous fibre reinforced components for the construction of vehicles requires the automation of the whole process. Short terms of tool occupancy and integrated means of quality control, included in automated processes, are the only way through which an economic mass production can be achieved. Figure 20.2 shows possible processes of manufacturing continuous fibre reinforced components, depending on complexity and quantity of the parts. Small quantities of parts can be produced as prepregs in different levels of complexity. The whole production is done manually. Components based on NCF are produced manually or are automated, depending on the number of units. Since NCF show limited drapability, the production of complex geometries based on NCF is not yet possible. Additionally, increasing complexity and quantity of components requires the simultaneous performance of several steps of production. Thus, the flexibility of the production process is decreased (Grundmann, 2009). The many advantages of continuous fibre reinforced materials over other, comparable materials can be seen in the flexible, lightweight design and very


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20.2 Production of parts of different complexity and quantity (Grundmann, 2009).

good environmental tolerance. The latter results from the small amount of raw materials needed for production and manufacturing, as well as the low fuel consumption, if used for vehicle components. Further spreading of continuous fibre reinforced composite parts runs aground on the low degree of automation in the production of corresponding component materials (Köth, 2003). Another reason is the high price for reinforcing fibres, which results from the low demand. This is also true if prepregs are used as raw materials. Preforms with reinforcing textiles have the potential of reducing production costs significantly by 20–30%. This is due to less expensive raw materials, less complicated terms of storage and the possibility of automation (Geßler et al., 2002). At present, the most prominent hindrance to an economic production of fibre-reinforced composite parts must be seen in the fact that textile preforms are not yet manufactured in an automated process and thus are neither cost efficient nor of constant quality. Contemplating the cost distribution for the manufacturing of a continuous fibre reinforced component in a preforming process, 50–60% of the component costs are generated during the preforming process (Fig. 20.3). Thus, new automated production processes for the manufacturing of fibre-reinforced composites made of NCF have to be developed. Although possible solutions for a partially automated production have already been developed, these works do not suffice to enable an economic manufacturing of fibre-reinforced composite components in practice. In this context, the research carried out within the framework of INTEX (Geßler et al., 2002) and PROPreform-RTM (Weimer et al., 2002) are worth mentioning. Further research activities focused on finding properties of components and methods for



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20.3 Distribution of costs in the prefoming process adopted by Gojny et al. (2008).

calculations, as well as the production of display models. These have been carried out within the framework of SPP 1123 (Hufenbach, 2007). In the European research project TECABS, a carbon fibre floor panel made of NCF was realised. Therefore, new technologies and methods have been developed with which up to 50 000 parts per year can be produced, by realising 50 units per day. This was achieved by developing RTM processes and new resin technologies, which allow fast production cycles and are cost effective. Also, the preform technology has been optimised to shorten the production time and to realise an integrated construction of the component to reduce the number of parts. In addition, different CAE tools have been developed in this project. Thus, the textile geometry can be described by the orientation of the yarns inside the textile. Further on, the mechanical performance of the reinforced structure can be predicted by building the stiffness of the matrix. The permeability of the textile reinforcement fabrics can also be simulated. The researchers were also able to develop numerical tools for quick simulation and to generate a tool to predict the costs (Verrey et al., 2006; Carrera et al., 2007). An automobile body made of continuous fibre-reinforced composites has been developed in the Japanese research project NEDO. In this project, new preform and RTM technologies have been developed to realise short cycle times. Beyond that, joining technologies for metal and reinforced composites have been generated, as well as simulation technologies for energy absorption. Additionally, recycling technologies for fibre-reinforced plastics have been examined (Takahashi et al., 2007).


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Automation of the whole process chain for mass production, optimisation of the flow of information with special consideration of interfaces, and a transfer to practice are prerequisites for an economical implementation of this technology. Only if these are achieved, can the technology arrive at medium-sized businesses, e.g. automotive suppliers.

20.2

Applications of non-crimp fabrics (NCF) in the automotive industry

20.2.1 Car roof, roof carline and hybrid constructions at BMW Group The first application of NCF in batch production of automobiles can be found at BMW AG, Munich, Germany. They employed NCF with 150 g/m2 and 300 g/m2 mass per unit area and fibre orientations of 0°, +45 and −45° (Derks et al., 2007). BMW AG, Munich, Germany, incorporates the process of preforming for the manufacture of components. For the production of the preforms, the required layers are made from the above-mentioned NCF. Between two layers, a binding agent is applied to keep the fibres in place. Before the stack of layers is shaped in the preforming tool, the semi-finished textile products are heated with an infrared spotlight. After the shaping, the semi-finished product is called a preform. One example of an NCF component produced by BMW AG, Munich, Germany, is the roof carline for the BMW M6. It has been realised as a glued shell construction (Fig. 20.4) (Derks et al., 2007). Another example for the serial use of textile-reinforced composite materials at BMW AG, Munich, Germany, is the roof of the BMW M3 (Fig. 20.5), which has

20.4 Roof carline BMW M6 (Derks et al., 2007).



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20.5 Roof of the BMW M3 (Frei, 2008).

been developed as a composite of a woven fabric and a glass NCF. Utilisation of a fibre-reinforced plastic structure for the roof resulted in a weight reduction of 5 kg compared to a conventionally built roof. In order to achieve a class-A surface, the outer shell consists of a carbon-woven fabric that is coated with a special clear varnish (Frei, 2008). BMW components are impregnated in a RTM process (Derks et al., 2007). The complete process chain from preform production to the assembly of the roof is shown in Fig. 20.6.

20.6 Industrial-scale manufacturing of the CRP-roof for BMW M3 (Frei, 2008).


468


20.7 Side frame of the BMW Hydrogen 7 (Derks et al., 2007).

NCF are also used for hybrid methods of construction at BMW Group, Munich, Germany. Within these, preforms consisting of NCF are glued to conventional body-part materials. Glue is spread across the complete surface of the preforms. Incorporating these hybrid constructions helps to improve the properties of the body and to meet crash regulations and stiffness requirements. A typical example is the side frame of BMW Hydrogen 7 (compare Fig. 20.7). Due to the very small quantity of required parts, at present, they are still laminated manually (Derks et al., 2007).

20.2.2 Boot lid of Lamborghini’s Gallardo Spyder Another example for the use of NCF-based components in the automotive industry is the boot lid of Lamborghini's Gallardo Spyder. The required properties of this component have been derived from a comparable part with an aluminum shell structure. Compared with the aluminum tailgate, which consists of nine single items and two additional plastic air outlets, the CRP component requires only two single parts. One inner and one outer shell need to be assembled, as can be seen in Fig. 20.8 (Derks et al., 2007). The realisation of this FRP boot lid includes UD and biaxial NCF with layers oriented in a 0°, ±45° and 90° direction. For the outer shell, carbon fibres are used, while the inner shell is produced with GFRP to reduce material costs. For the manufacturing of fibre-reinforced components from textile preforms, the RTM process is employed. Due to the homogeneous surfaces produced by the viscous resins used for RTM, the potential for achieving class-A surfaces with the RTM process is higher than with prepreg systems (Derks et al., 2007). The cycle time for the production of a tailgate is 30–45 minutes. The painting of the boot lid is realised offline, in order to spare the component from the high temperatures of online painting. With this component a weight reduction of 5 kg, as compared with the aluminum part, could be achieved. At the same time a class-A surface is realised (Deinzer et al., 2007). The readily produced and built-in part can be seen in Fig. 20.9.



469

20.8 Integrated construction (Deinzer et al., 2007).

20.9 Lamborghini Gallardo Spyder with built-in FRP boot lid (Deinzer et al., 2007).

20.3

Research and development for the use of NCF in automotive applications

Currently, automated process chains with short cycle times for production of continuous filament plastics based on NCF are a major obstacle for the


470


establishment of NCF in the automotive industry. Today, fibre-reinforced plastics based on NCF are manufactured in a manual preforming process. To expand the lightweight construction and use of continuous fibre reinforced plastics in the automotive industry, there are different research approaches for the development of automated process chains. Thereby, there is a distinction between single-step and multi-step preforming.

20.3.1 Single-step preforming The single-step preforming is characterised by the fact that a near net-shaped textile preform with variable thickness and variable layer structure is produced in a single production step. The braiding process is actually used as single-step preforming in industrial applications. An example, therefore, is the overbraiding process used for front and rear bumpers in the BMW M3 series manufactured by SGL Kümpers GmbH, Lathen, Germany. Other single-step preforming processes like multiaxial warp-knitting are currently developed with the aim to produce NCF with individual layer construction in order reduce waste and expenditure of work. The focus of a research group (FOR 860) at RWTH Aachen University, Germany, is to develop economic mass production of structural components made of continuous filament plastics based on NCF for automotive applications. There the single-step preforming of NCF is used, for which an integrated modular machine concept was developed that is able to produce continuously semi-finished fabrics on the basis of NCF. The results are tailored NCF. They have the properties of finished reinforcing structures and the novel developed production process is able to reduce handling processes and further production steps. In doing so, local reinforcement structures like, for example, 0° layers or additional NCF can be integrated into the manufacturing process. A picture of this newly developed feeder module is shown in Fig. 20.10. With this feeding module for multiaxial warp-knitting machines, reinforcing structures for high-volume applications can be realised (Greb et al., 2009; Kruse et al., 2009). In addition to producing adjusted NCF, the aim of research is to be able to adjust the drapability of NCF locally in the direction of the manufacturing process, without interrupting the production process. Thereby the drapability is especially affected by the warp-knitting stitch pattern and the tension of the knitting thread. The lower the thread tension, the easier the reinforcing fibres can move within the meshes. A certain amount of tension is needed to ensure a good bond between the individual layers and to avoid undulations (Hufenbach, 2007). Considering these circumstances, it is the aim to realise high drapability in special areas of the textile by varying bond type and tension thread locally. To change the binding continuously during the production process, a new electromechanically driven guide bar was developed. With these enhancements of the warp-knitting machine, it is possible to produce pre-assembled NCF which have a locally recruited



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20.10 Feeding module for multiaxial warp-knitting machines (Kruse et al., 2009).

drapability. Thus it is possible, for example, to produce the desired fabric with the appropriate characteristics and an adjusted drapability in certain areas for a particular component (Greb et al., 2009; Kruse et al., 2009). In addition to this, Cetex GmbH, Chemnitz, Germany has developed a variable delivery for filaments on multiaxial NCF. Hereby, it is possible to realise reinforcing fabrics for plane faces, shells and nodes elements. In this project, the multiaxial warp-knitting machine has been equipped with an additional module. This module can realise a displacement of the chaining thread and can change the concentration of the chaining thread by storing individual rovings or filaments. This is achieved by a folding gate with thread guides, see Fig. 20.11 (Heinrich and Vettermann, 2009). With this additional module, the following yarn displacements can be realised (examples in Fig. 20.12). This recently developed process technology to manufacture customised reinforcement structures was verified by a demonstrator component. The demonstrator was a locally reinforced tank wall from the automotive industry. With these two developments for the production of adjusted textile on the basis of the multiaxial warp-knitting technology, reinforcing structures can be manufactured cheaper and more automated. Therefore,


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20.11 Folding gate with thread guides (Heinrich and Vettermann, 2009).

20.12 Possible reinforcement yarn displacements (Heinrich and Vettermann, 2009).

reinforcement fabrics are produced with a fibre orientation that corresponds to the loading cases of the component. Thus, a near-net shape manufacturing of planar components, such as tailored NCF, can be realised in one process step and the processing time for the manufacturing of automobile parts on the basis of these semi finished products can be reduced.

20.3.2 Multi-step prefoming The production of a near-net shaped textile preform in a multi-step preforming process is a result from several production steps. Using the multi-step preforming



473

it is possible to produce components with a high complexity. First, NCF or woven fabrics and other sub-preforms, like braided structures, are manufactured. By bringing together the semi-finished textile products in a preformed tool with the production steps cutting, handling and draping, a near-net shaped preform is created, which is fixed by joining or binder application. In various research projects (Geßler et al., 2002; Hufenbach et al., 1999) procedures for individual steps of the preform manufacturing process have been compiled. These procedures were developed and investigated separately. As a result, separate tailored solutions for the individual process steps are available. In order to be able to produce components automatically, a flexible manufacturing cell for the production of three-dimensional textile preforms was realised at the Institute für Textiltechnik, RWTH Aachen University, Germany. Figure 20.13 shows the manufacturing cell, which is known as the preform centre. In this manufacturing cell, a robot is equipped with a tool changing system that can implement automatically the individual steps which are necessary for the production of fibre-reinforced plastics on the basis of NCF. By using a tool changing system, it is possible to equip the robot with different tools (Fig. 20.14). For the illustration of a process chain for the production of three-dimensional textile preforms, the following tools are available: • • • • •

gripper, sewing heads, tufting head, binder application system and quality monitoring.

By changing the different tools, it is possible to produce textile preforms in a single manufacturing cell in an automated way. The testing of this manufacturing cell was examined using examples from the automotive industry. The results are presented briefly below.

20.13 Preform centre (Grundmann, 2009).


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20.14 Production steps in a preform centre.

Car roof segment Using a car roof segment, a semi-automated process for the manufacturing of this component was developed in the research project ‘AutoPreforms’. This component is realised using four layers of a multiaxial NCF with a lay-up of 0° / 90°/ +/−45°. The mass unit per area of the NCF used is 840 g/m2. In order to receive an aesthetic carbon appearance, a woven fabric is used as a top layer. In addition, metal inserts are integrated into the component to allow the mounting of attachment parts. Profiles with integrated foam core are used to stiffen the component design. These profiles are made as preforms, prior to the actual manufacturing of the roof segment. These pre-produced parts integrated into the preforming process of the roof segment are called sub-preforms. To realise the profiles, NCF were draped around a foam core and secured by seams. A schematic diagram of the realised component is shown in Figure 20.15.



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20.15 Preform of a roof segment (Grundmann, 2009).

During the production process of the roof segment, first the sub-prefoms are manufactured manually. The roof segment is then manufactured fully automated in a preform centre. First, the textile semi-finished products are cut at the cutter table and then draped in the mould using a gripper. Before the next textile layer is applied, binder is applied to ensure fixing of the layer system. These steps are repeated until the desired layer stack is obtained. In addition, the metal inserts are integrated into the textile preform. After the desired layer stack is realised, the sub-preforms are applied to the shell element and then fixed by sewing. Automobile underbody structure The production of an automobile underbody structure was also realised with a semi-automated process. Figure 20.16 shows the complete manufacturing technique of an automobile underbody structure on the basis of NCF. First, the needed NCF layers are cut and then draped into the mould. For the integration of attachment parts, metallic inserts are integrated into the textile preform during the preforming process. To realise this component, a large number of manual handling steps are required, since there is no automated draping process for these complex geometries. By using a braided side skirt, the production process is more economical, because the number of handling steps is reduced (Grundmann, 2009). In addition to this, complex draping tools have to be developed which significantly simplify the draping in the mould and reduce the cycle time for the component manufacturing. Grundmann has developed a software tool to analyse the process chain assessment, which deals with the economics of the textile preforming and can help to optimise the existing preforming processes (Grundmann, 2009).


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20.16 Preforming of an underbody structure (Grundmann, 2009).

20.4

Future trends

Due to rising oil prices and legislation introduced to reduce carbon dioxide emissions, the need for lightweight structures in automotive applications is constantly growing. The aim is to reduce the weight of vehicles, because driving resistance is linked directly to the car’s weight. Beside the use of new metals and aluminium, one approach to achieve that aim lies in the use of textile-reinforced composites, which provide high strength and high stiffness at a low weights. Today, composites are expensive high-performance materials, which find their applications in small series and niche markets (Fig. 20.17). To establish NCF in the field of new lightweight structures for applications in automotive engineering, there is still the need for extensive research. The target is to make composites based on NCF into a high-performance material for mass



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20.17 Trends in fibre-reinforced composite production.

20.18 Comparison of steel and textile production lines.

production with great potential for material and energy conservation. Therefore, new production technologies are needed which are able to cope with the challenges of large-scale serial production. Looking at the metal industry, special tailored materials like tailored blanks and tailored tubes have been developed (e.g. ThyssenKrupp). These components have the advantage of combining weight reduction with economic production methods. Tailored blanks are characterised by homogeneous thickness of the final part independent of the degree of deformation. Before forming a final part with a complex geometry, tailored blanks are flat metal sheets which provide local differences in thickness. In tubular forms, tailored tubes are available and have the same advantages as tailored blanks. These special tailored components are used in the automotive industry for body structure systems and are finally joined using robot-assisted handling and metal joining technologies like conductive welding (Fig. 20.18).


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To be competitive in this market with textile-reinforced structures made of NCF and other textile fabrics, new production technologies for near-net shape reinforcement structures (tailored NCF and tailored braid) which enable economic large-scale production have to be developed. Compared to the metal process, textile structures equivalent to the tailored blank and the tailored tubes already exist today or are currently being developed in research projects. Tailored noncrimp fabrics are comparable to tailored blanks (Fig. 20.18). These textile products can be manufactured in a single-step preforming process using multiaxial noncrimp fabric technology. Thus, local changes in the thickness of the NCF during the production process can be realised. By locally varying knitting patterns and stitch length in addition to the changes in thickness, the drapability of these fabrics can vary locally. To achieve a defined geometry for a special component, the tailored NCF will be cut to the required dimension. Textile production technologies equivalent to the metal tailored tube process are overbraiding, 3D weaving or 3D braiding (Fig. 20.18). These production processes are capable of realising changes in cross-section geometry, local changes in thickness and to produce shaped textile tubes and profiles. Combined with pultrusion technology, constant profile geometries can be realised. For the production of a textile-reinforced component with complex geometry, robot-assisted handling and joining technologies are available for the processing of textile reinforcements. To handle the textile fabrics and the textile preforms (tailored NCF and tailored braids) during the multi-step preforming process, cryogrippers (ice-grippers) and needle-grippers can be used. In addition, textile joining technologies exist for an automated robot-assisted production. This can be done using blind-stitch technology, tufting technology or similar one-sided sewing technologies. These automated textile handling and joining technologies are used for the assembly of textile sub-preforms like tailored braids or tailored NCFs. These production technologies, which are currently developed and optimised, represent the key to large-scale production of textile-reinforced composites for automotive applications based on NCF. To make these automated textile process chains even more economical, Grundmann (2009) developed a tool for planning effective production chains. The whole picture of an integrated development and implementation of the full textile process chain cannot exist without integrated virtual production planning. Thus, especially for multi-layered integrated reinforcements, virtual tools for the simulation of the geometrical shape, the draping behaviour and of course for the calculation of the mechanical properties for the dimensioning of the final part are required and currently under investigation at various research institutes.

20.5

Conclusion

At present, there are several applications of reinforced components made of NCF in single high-performance vehicles on the market. In order to establish



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textile-reinforced components made of NCF in the automotive industry, new production technologies have to be developed, which are able to meet the challenges emerging with large-scale production. One major step towards this aim is to develop automated preforming technologies which allow short, and therefore economical, cycle times. Furthermore, quality assurance systems, especially for certified products like automotive parts are needed and have to be developed and implemented in new production chains. Today, textile technologies already provide promising, but so far isolated solutions. Combining these solutions and adapting them to the individual needs of the automotive industry together with adjusted simulation tools will eventually lead to the breakthrough of these textile production technologies, especially for NCF in automotive applications.

20.6

References

N.N., Waldeckische Landeszeitung Frankenberger Zeitung, Osnabrück, Germany, http:// www.wlz-fz.de/Welt/Kultur/Uebersicht/Reise-durch-Automobilgeschihte (accessed 18 January 2010). Berger L, Lesemann M and Sahr C (2009), ‘SuperLIGHT-CAR: innovative Multi-MaterialBauweise’, Leightweight design, vol. 2, no. 6, pp. 43–49. Carrera M, Cuartero J, Miravete A, Jergeus J and Fredin K (2007), ‘Crash Behaviour of a Carbon Fibre Floor Panel’, International Journal of Vehicle Design, vol. 44, pp. 268–281. Deinzer G, Reim H, Hermes C, Schneidewind T, Masini A and Enz J (2007), ‘Class A mit CFK – Beispiel Heckklappe Gallardo Spyder’, in VDI (ed.), Kunststoffe im Automobilbau, Düsseldorf, VDI. Derks M, Birzle F and Pfitzer H (2007), ‘CFK-Technologie bei der BMW Group – Heute/ Zukunft’, in VDI (ed.): Kunststoffe im Automobilbau, Düsseldorf, VDI. Ehrenstein G (2006), Faserverbund-Kunststoffe: Werkstoffe: Verarbeitung, Eigenschaften, 2nd edn, Erlangen; München; Wien, Hanser. Feraboli P and Masini A (2004), Development of carbon/epoxy structural components for a high performance vehicle, Composites Part B, 35, 323–330. Frei P (2008), Serienfertigung von Faserverbundstrukturen am Beispiel des BMW M3 CFK-Daches, in AVK (ed.), Tagungshandbuch der 11. internationalen AVK-Tagung: 22–23 September 2008, Messe Essen, Essen, AVK– Industrievereinigung Verstärkte Kunststoffe e.V. Geßler A, Gliesche K, Keilmann R, Laourine E, Kröber J and Pickett A (2002), Textile Integrationstechniken zur Herstellung vorkonfektionierter Verstärkungsstrukturen für FVK “INTEX”: BMBF 03N3060, Ottobrunn, EADS. Gojny F, Heine M and Kümpers F.-J (2008), ‘Verarbeitungstechnologien für Kohlenstofffasern’, in Composites in Automotive & Aerospace, Materialica 2008, München, 16.02.2008, S. 6 Greb C, Schnabel A, Kruse F and Gries T (2009), Automated Production of Textile Preforms for Structural Fibre-Reinforced Plastic Components, in Küppers B (ed.), 2nd Aachen Dresden International Textile Conference, Aachen, DWI an der RWTH Aachen. Greulich S (2007), Biopolymere für den technischen Eunsatz im Automobilbau, in VDI (ed.), Kunststoffe im Automobilbau, Düsseldorf, VDI. Grundmann T (2009), Automatisiertes Preforming für schalenförmige komplexe Faserverbundbauteile, Aachen, Shaker.


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Heinrich H-J and Vettermann F (2009), ‘Gestaltungsmöglichkeiten für bionische Verstärkungsstrukturen durch variable Filamentablage auf Multiaxialgelegen’, paper presented to the scientific meeting 48. Chemiefasertagung Dornbirn, Dornbirn, 16–18 September 2009. Hufenbach W (ed.) (2007), Textile Verbundbauweisen und Fertigungstechnologien für Leichtbaustrukturen des Maschinen- und Fahrzeugbaus: textile Verstärkungen Halbzeuge und deren textiltechnische Fertigung, Dresden, SDV – Die Medien AG. Hufenbach W, Rödel H, Langkamp A and Herzberg C (1999), ‘Beanspruchungsgerechte 3D-Verstärkungen durch funktionsgerechte Nähtechnik’, paper presentet to the scientific meeting Materialica 1999, München, 27–30 September. JEC (ed.), Composite Materials in Automotive, Paris, JEC Group, 2007. Köth CP (2003), ‘Pulver, Kohle, Kosten: ein neuartiges Pulver senkt die Herstellungskosten von CFK- und GFK-Verbundwerkstoffen; die Serienanwendung rückt damit in greifbare Nähe’, Automobil Industrie, vol. 48, no. 3, pp. 94–95. Kruse F, Schnabel A, Behling T and Gries T. (2009), ‘Automated textile preforming of semi-finished fabrics for the mass production of fibre-reinforced plastic components’, paper presented to the scientific meeting ITMC 2009 : Intelligent Textiles and Mass Customisation, Casablanca, 12–14 November. Räckers B (1997), ‘Faserverbundwerkstoffe, Entwicklungstrends am Beispiel des Airbus’, in Friedrich K (ed.), Verbundwerkstoffe und Werkstoffverbunde, Frankfurt am Main, DGM Informationsgesellschaft, pp. 3–14. Schauerte O, Schreiber W, Finkbeiner A, Ene E and Starmann D (2007), ‘Der Einsatz von leistungsfähigen Kunststoffen im Bugatti Veyron’, in VDI (ed.): Kunststoffe im Automobilbau, Düsseldorf, VDI. Takahashi J, Uzawa K, Ohsawa I, Kitano A, Yamaguchi K and Usui K (2007) ‘NEDO Project “Automotive Light Weight Structural Elements of CFRP Composites”: Recycle and LCA’, Journal – Society of Automotive Engineers of Japan, vol. 61, 10, pp. 47–51. Verrey J, Wakemann M D, Michaud V and Manson J-A E (2006), ‘Manufacturing cost comparison of thermoplastic and thermoset RTM for an automotive floor pan’, Composites: Part A, vol. 37, pp. 9–22. Weimer C, Mitschang P and Neitzel M (2002), ‘Continous manufacturing of tailored reinforcements for liquid infusion processes based on stitching technologies’, in Bhattacharyya B (ed), 6. International Conference on Flow Processes in Composite Materials, Auckland, University of Auckland, Department of Mechanical Engineering, Paper No. FPCM6-DE–2.


21 Non-crimp fabric composites in wind turbines G. ADOLPHS and C. SKINNER, OCV Technical Fabrics, Belgium

Abstract: Historical development and modern use of non-crimp fabric (NCF) in wind energy applications such as blade and nacelle are given. The influence of fabric processing such as skewing, resin infusion and pre-impregnation (prepreg) are also shown. Key words: wind energy, blade design, specific strength, resin infusion, nacelle design.

21.1

Introduction

21.1.1 The oil crisis as the initiator for wind energy The trigger for the development of the modern wind power industry is often described as the energy crisis of 1973. The ‘oil price shock’ of 1973 initiated a public debate about the dependence of Western economies on oil imports so, in addition to energy saving measures, politicians turned their attention to the search for alternative energy sources. This led to the development of many programmes, such as the those sponsored under the US Federal Wind Energy Programme (1973),1 the formation of the National Swedish Board for Energy Source Development (1975), a range of experimental turbines in Denmark and a range of government subsidised programmes in Germany led by the Bundesministerium fur Forschung und Technologie, which ultimately led to the construction of the ‘Growian’ (Gross Windkraft-Anlage) which gained much notoriety.2,3 In many cases, these extensive government-funded programmes resulted in little tangible development of the industry and, after the crisis, only one country demonstrated the consistently successful operation of wind turbines: Denmark. The basic technical concepts of the turbines employed had been developed in the beginning of the 20th century by Poul La Cour (Askov, Denmark), Albert Betz (Göttingen, Germany) or Palmer Cosslett Putnam (Vermont, USA) and had found relatively widespread adoption due to the superiority of the design due to the following characteristics. • •

Sleek, fast-running propeller designs which produce low thrust at high torque and can more easily withstand high wind speeds. Rotor speed and power output can be controlled by pitching the blades and this also provides effective protection against extreme wind speeds. 481 © Woodhead Publishing Limited, 2011

482 •


Fibre-reinforced composite materials allow aerodynamically optimised shapes and enabling highest efficiency of the unit while being lightweight, fatigue and weather resistant.

In this area some small- and medium-sized manufacturing firms in Denmark, for example, VESTAS, seized an opportunity of constructing these three-blade rotors and grid connections and started to sell these wind turbine concepts to private owners or farmers. These were typically small units (60 kw) with rotors of 15–16 m. In 1986, these units contributed ∼1% of Denmark′s power requirements, but from this point began to grow exponentially based on clearly defined permits and the availability of appropriate testing stations.

21.1.2 The evolution material choice in wind rotor blade technology Rotor blade technology for these wind turbines has evolved in the 40 years since the ‘energy crisis’ of the 1970s and now can be associated more with lightweight aeronautical engineering than with conventional mechanical engineering.4,5 In contrast to all other components of the turbine which can be ‘borrowed’ for existing fields of engineering, the rotor blades must be developed to match the load spectrum of a given turbine. However, in contrast to aircraft engineering the cost structure of wind energy operation prohibits traditional aircraft manufacturing methods and production technology and was adopted from other fields. In the case of rotor blades the transfer primarily comes from the modern boat building and industrial engineering where fibreglass composites predominate.6 The rotor blades of older Danish wind turbines were almost always manufactured by former boat builders. In the past, the starting point for rotor blade design was the question of which material would be the most suitable. Design and manufacturing methods are in reality determined by which material is the most suitable. In other words, it is impossible to separate material and manufacturing process. Analysis of materials common in aerospace engineering highlights the following materials as ‘suitable in principle’ for rotor blade construction.7 • • • •

Aluminium. Titanium. Steel. Fibre composite material (glass, carbon, aramide).

The most important properties by which a first assessment can be made are • •

specific strength (strength/density); modulus of elasticity;



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21.1 Comparison of unit material cost per unit of strength for a beam in bending under a cyclic load analogous to a wind rotor blade.9

• •

specific modulus (modulus of elasticity/density); ∧ ∧ fatigue strength after 10 7 to 10 8 load cycles.8

Comparison of the material properties highlights that the excellent balance of properties exhibited by fiber glass/epoxy composites making them ideal choices for delivering cost effective strength in engineering configurations as found in wind rotor blades. Figure 21.1 shows different material options in terms of their specific strength and specific cost performances. Fibre glass/epoxy has both a low mass and cost per unit of strength which explains its adoption as the material of choice for rotor blades.

21.2

Development of non-crimp fabric (NCF) composites in wind energy

21.2.1 The impact of infusion technology on NCFs


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21.2 Blade length over time, main years of build of different blade lengths.

21.2.2 Traditional woven structures in wind rotor blades From the inception of the wind energy industry in Denmark, the materials chosen for the construction of the wind rotor blades for fibre-reinforced composites was based on reinforcing structures taken from the boat building industry. From the mid-1970s, the reinforcement materials typical used in the construction of composite craft were: •

woven roving using plain ligament and equal amount in warp and weft fibre in 300, 500, 600 and 800 gr/m2 total area weight;

21.3 Typical blade design, middle section, two shear webs, source: presentation M. Zvanik, Owens Corning and DIAB, CFA Show 2001, Tampa, Florida.


Non-crimp fabric composites in wind turbines • •

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combination of these typical woven materials produced in combination with chopped fibre mat of 300 and 450 gr/m2, creating combination products, mostly used were woven roving of 500 and 600 gr/m2 and mat of 300 gr/m2; and unidirectional woven roving of 600 gr/m2 and 800 gr/m2, later as well of 1200 gr/m2 having a percentage of warp reinforcement of usually 90%.

Instead of using +/−45° biaxial non-crimp fabric (NCF) woven fabrics were laid up at an angle of 45° converting warp in +45° and weft in −45° or vice versa. A typical blade design during this period was using the unidirectional (UD) fabrics to form spar caps, woven fabrics for the skin structure and shear web and complexes for the coupling area.

21.2.3 Introduction of skewed fabrics in the late 1980s An evolution in the construction of reinforcements for the wind rotor blades was the use of skewed fabrics in the late 1980s. In this process a woven weft UD is skewed to a 45° fabric during winding or unwinding and at the same time another woven fabric is skewed to −45°. During the assembly process the individual fabrics are combined by a warp-knitting operation similar to the combination structures described earlier. Figure 21.4 shows this process schematically. The process also allowed the addition of chopped fibre to modify the infusion

21.4 Schematic of a typical skewing process using a Malimo or Liba knitting machine.


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characteristics of the complexes. The materials from this type of process are still in use today in the construction of wind rotor blades. Another option was during the 1980s and 1990s to use sequential weft insertion warp-knitting machines which produce a weft UD fabric and skew this fabric to the desired +45° or −45° angle and assemble two skewed fabrics with or without chopped. As the knitting operation inserts the weft yarns one by one, they were already NCF by today's standards. However, the described skewing and assembly process causes fibre misalignment and distortion of the selected fibre orientation. Both effects have shown inferior mechanical properties.10 During the 1980s it was as already possible to produce +/−45° structures in a direct process by early weft-laying NCF machines, but they lacked a suitable adjustment to produce true parallel weft. The weft structure was crosslaid and the resulting mechanical laminate properties were inferior to the true parallel weft insertion materials. As these materials were expensive, they were used to little extent. Production methods used by the vast majority of blade producers were still hand lay-up.

21.2.4 Vacuum-assisted resin transfer and the growth of NCFs To make the blade longer and aerodynamically more effective, the materials needed to improve. For a longer blade an increase in material stiffness is desirable and more valued. Appropriate scaling factors which relate properties to rotor diameter have been published.11 Importantly, for the development of the wind rotor blade technology a new process technology was developing. The vacuum-assisted resin infusion process or vacuumassisted resin transfer moulding (VARTM) or vacuum infusion process (VIP) became increasingly popular. This methodology allowed an increment in material stiffness by incrementing the fibre volume fraction from 35% to 40% fibre volume fraction (FVF) typical of a hand lay-up to 50% to 55% FVF by the VARTM process. The effect on laminate tensile stiffness made out of UD NCF fabrics is an increase from approximately 25–30 GPa to over 37 GPa, which means an increase of around 25%. In woven structures, a higher area weight causes a dense structure of reinforcement material which needs to be interlaced, which causes increased crimp of the reinforcement fibre. In an NCF this effect is drastically reduced as reinforcement fibre is laid parallel and the formed ply of reinforcement is laid one over the other. The new vacuum processes not only delivered an increment in mechanical properties. Heavyweight NCF could still be impregnated and a high fibre volume fraction could be achieved. The combination of both the NCF reinforcements and the VARTM process allowed wind blade producers to benefit from the improved cost and reduced production time which offered this combination. Reduced costs and higher stiffness facilitated the development of longer and more efficient blades.



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Table 21.1 Possible and frequently used warp weight (in bold) in unidirectional materials Warp roving Gauge [tex] [yarn/inch]

[yarn/cm]

1200 1200 1200 1200 1200 1200 1200 1200 2400 2400 2400 2400 2400 2400 2400 2400

1.97 2.36 2.76 3.15 3.54 3.94 4.72 5.51 1.97 2.36 2.76 3.15 3.54 3.94 4.72 5.51

5 6 7 8 9 10 12 14 5 6 7 8 9 10 12 14

Area weight [gr/cm2] 236 283 331 378 425 472 567 661 472 567 661 756 850 945 1134 1323

Many of these early NCF materials used in the VARTM processes were UD materials. The main glass roving available were 1200 tex and 2400 tex, and rarely 1500 tex and 2200 tex. Taking usually available knitting machine elements the following area weights shown in Table 21.1 could be produced, with the highlighted combinations being the more frequent versions observed in the industry. Apart from the UD NCF, multiaxial fabric as +/−45° biaxials are needed in the laminate design of modern windmill blades. During the 1980s the first parallel weftproducing multiaxial warp-knitting machines were presented and allowed the production of true parallel weft at adjustable angles ranging from 90° to around 30°. As well as with UD fabrics, a range of biaxial fabrics established itself as a function of available glass roving and cost efficiency in production.12 Early version of these fabrics have been produced using 68 tex to 134 tex glass yarn and +/−45° fabrics of around 300 gr/m2 were produced. The laminate thickness in longer blades increased. Heavier area weight could be used. Consequently 200 tex direct roving was used to produce biaxial fabrics of 450 gr/m2 and today 300, 600 and 1200 tex direct roving is used to produce +/−45° biaxial fabrics of 800 gr/m2, 1000 gr/m2 and above.

21.2.5 Development of weft technologies in NCF reinforcement structures Over time the machine technology also allowed a more precise insertion of weft yarns. While in many older machine configurations the weft lay-up was not


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21.5 Description of typical weft insertion possibilities using NCF production machine.

synchronised with the exact production speed, cross weft or substantial parallel weft was inserted as shown in Figure 21.5. Modern-day machines for the production of NCF structures with numerical control allow for the construction of true parallel weft. As consequence of the irregular crossover of weft reinforcement local small defects are common in the types of fabrics resulting in lower mechanical properties. A more tailored used of multiaxial material can be found in the production of substructures of wind rotor blades as, for example, flanging rings. These are designed to allow the blade to be screwed to the cone and are coupled with the main blade laminate. This construction can be prepared by infusion together with the main shell or potentially produced as a separate part and are assembled in a final production stage by structural adhesives. The screws can be of a T-bolt type or carrot type, glued in screws. The T-bolt type needs in general a laminate design adequate to absorb the shear loads and pressure caused by the T-bolt and its design is similar to laminate designs for riveting with an approximate amount of 50% UD and 50% of a +/−45° biaxial oriented fiber.13 An example can be named a flanging ring build-up by winding 45°/90°/−45° in 200/400/200 gr/m2 triaxial fabric. A glued-in screw can in general terms build up by much higher UD-oriented designs. An example is a flanging ring build-up by +80°/0°/−80° 300/60/300 gr/m2 oriented NCF multiaxial fabric produced in a fabric winding operation. Generally, it is possible to describe the construction of a typical wind rotor blade using NCF reinforcement structures using a range of typical styles as in Figure 21.5.14 As it can be seen in Plate XIII (see between pages 396 and 397), a substantial part of the laminate is build-up by UD and triaxial NCF fabrics. In common designs, the UD NCF portion in a modern wind rotor blade is 50–60% of the NCF fabrics. Triaxials are reduced in favor of UD and biaxial +/−45° fabrics in bigger blades. Shear webs are build mainly using NCF constructions of +/−45° materials. In such designs a critical area in a blade is the large flat surface area towards the root. In this area the loads are more complex caused by combinations of air pressure, flap-wise deflection and edge-wise deflections. Local stress concentrations can occur and buckling can be caused in the compression zone under deflection. An image from possible buckling is described in Fig. 21.6.



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21.6 Buckling simulation of a blade (Locke J., Valencia U., ‘Design Studies for Twist Coupled Wind Turbine Blades’, SAND 2004-0522, Albuquerque/Wichita, USA).

21.2.6 The use of UD prepregs in wind rotor blade design An alternative design option developed by Danish wind rotor blade manufacturers is shown in Fig. 21.7. The figure highlights that in this construction the shear web construction commonly associated with the VARTM process to produce a full blade have been replaced by a central ‘wingbox’ structure. The top and bottom of these constructions are built up using UD reinforcements and both sides have the function of the shear web. The box structure holds approximately 85% of the mechanical load and is covered by a fairing that is glued on. The UD structure is composed of UD prepreg and biaxial dry fabrics. Other biaxial prepregs build up the sidewalls together with core material, forming said shear web. The fairing is designed using a combination of triaxial and biaxial prepreged NCF fabrics and core materials. Pre-impregnated reinforcement fibre and fabrics, a material type and related vacuum-bagging process used mainly for aerospace part manufacture, show, as the infusion process, a clear improvement in mechanical properties versus the hand lay-up process. As the materials used are pre-impregnated, their commercial use requires a refrigerated supply chain, a precise cut, lay-up and debulking process to remove trapped air in between the material layers. A common step in the process in aerospace applications is to use an autoclave to compact the material under higher


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21.7 Central spar design typical of those used commercially by VESTAS and Gamesa.

than atmospheric pressure. Because of the immense size of wind turbine blades and their components or subparts this cannot be done for economic reasons. However, tools must be heated up to around 80°C to cure the used epoxy resin system. The UD prepreg approach, however, holds some advantages with respect to NCF, as it can be made of 100% oriented fibre structures in an UD direction, no weft is necessary and the amount of resin can be precisely adjusted to the required tolerances and the resins can have higher viscosity than resin systems used for the infusion process. Triaxial and biaxial prepreg show no or little differences to material used in the infusion process and demonstrate very similar mechanical properties. The reason is that those prepregs are made entirely out of the same NCF. With respect to the use of carbon fibre for UD structures as spar cap (or girder) the UP prepreg process offer some advantages. • •

The impregnation process can be controlled and adjusted to produce a full impregnation of the carbon fibre prior to their use in the moulding application. The impregnation process can be adjusted to increment the amount of resin in the UD prepreg vs. VARTM thus reducing the fibre volume fraction. This reduces overall material cost and reduces the carbon prepreg laminate modulus. The reduction in modulus improves the compatibility with glass fibre prepreg in hybrid carbon–glass designs too.

The major loads that wind rotor blades are subjected to aerodynamic loads as thrust and lift on the blade. Thrust is causing a flap-wise deflection, aerodynamic lift causes a mixed flap and edgewise bending and the torque to spin the rotor and produce energy. Torsion loads twisting the blade along their axis are caused by thrust and lift. The blade mass is subject to both gravity and inertia loads. Gravity loads pull the blade down and act as an edgewise load. Inertia loads are caused by the rotation and by vibrations. Lower masses and reduced vibrations reduce substantially these loads (Plate XIV).15 All these loads cause multiple static and dynamic stresses which any material used on the construction of a wind rotor blade must be able to withstand over the designed lifetime which is commonly between 20 and 25 years. To determine the suitability of a reinforcement material for this operating environment a range of tests are therefore carried out to show the suitability of the used materials. These



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are described by standards edited by the main certification bodies.16 All NCF materials to be used in a wind rotor blade have to be tested according to these standards. The main parameters are • • •

tensile strength and modulus in reinforcement direction and transversal direction; shear strength and modulus; and fatigue strength in three different load ratios up to two million load cycles.

Another important parameter is the thickness of the fabric used. As wind rotor blades are built by lay-up of individual NCF or prepreg layers, at each start and end of a new layer, a drop in laminate thickness is generated. This causes a sudden difference in laminate properties and a shear tension at the cut edge of the new layer in the boundary between new layer and existing laminate. The material design must withstand the deformation at these boundaries over time. Another specific requirement is caused by frequent lightning strikes to wind energy converters. NCF materials that are used in wind turbine blades must, in addition, show a uniform dielectric behavior and must not offer undesired local conductivity.

21.3

NCF materials used in nacelle construction

In almost all horizontal wind energy converters, the key components of the machine are housed in a closed nacelle on top of the tower as a prolongation of the turbine axis. In reality, the design concept of the nacelle is defined by the arrangement of the drive turbine and the generator. Ease of assembly and total cost are also key defining factors in the nacelle construction. The most common design is of either a welded bedplate or a cast bedplate, on which the non-load bearing structure is attached. Various materials have been used for this non-load bearing structure such as aluminium or steel structures. Because of their light weight, facility to be designed in distinctive free-form designed shapes, very good corrosion and weather resistance, these shells have been made using glass fibre reinforced composite materials for the past decades. The nacelle design and production methods have followed closely the evolution of rotor blades. At one hand, most of the designers used in dimensioning and layout of blades worked in the design and laminate layout of nacelles, and on the other, the requirements with regard to lifetime, weight and cost are similar. So it is no wonder that when hand lay-up dominated the blade manufacture, nacelle covers, as shown in Plate XV, were initially produced in a hand lay-up processes, but when blade manufacture went to infusion processes, the nacelle production went too. Today there are two basic processes used. One is VARTM, as used in blade manufacture, but using the more convenient 0/90 biaxial NCFs instead of more costly biaxial +/−45° laminates, and, to build up the required


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thickness as well, a combination products of NCF with mat, sometime with enhanced resin flow properties. The other process applied is RTM light where a rigid mould and semi-flexible counter (male) mould is used. Advantages of this system are both outside and inside smoother finishes, but the resin amount needed is higher. A compressible reinforcement material is needed too which increases cost.

21.4

Future trends

Currently there are several issues related to the future use of NCF in the efficient construction of wind rotor blades. Production consistency One of the major concerns is the high irregularity of mechanical properties as a consequence of fibre misalignment, local imperfections as missing or displaced reinforcement fibre and wrinkles of the reinforcement structure formed in the laminate. Other issues can be attributed to material and processes variations. Foaming of the resin, incomplete wet-out, or an excessive exothermic reaction or ‘heat generation’ during the reaction of the used resins cause a further deterioration of the laminate properties. Even though the required security factors against failure are estimated on statistical requirements lower than in aerospace applications the level of inherent over design due to these factors has an increasing impact as blades become longer and heavier in the drive to lower of cost of electricity generation through wind power. Manufacture of larger and longer blades To be able to produce bigger and bigger blades and due to the challenge of transporting structures higher than 5 m in a cost-effective manner, new concepts have been evolved. One possibility is to build a blade in segments or sub-assemblies which are assembled or produced as preassembled dry structure, so called preforms. These parts are either infused as a whole or, if produced independently, assembled using structural adhesives. Examples of this type of approach are pioneered by companies such as Blade Dynamics (Plate XVI). Optimisation of the aerodynamic performance of wind rotor blades In the drive to constantly reduce the cost of wind energy, there is a tendency to the production of sleeker and aerodynamically more efficient blades. To realise these types of designs, the requirement for sophisticated fibre and NCF fabric properties increases, providing another challenge for the producers of NCF reinforcement structures.17



21.5

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References

1. Goodmann Gr., F. R; Vachon W.A.; United States Electricity Utility Activities in Wind Power, Fourth International Symposium on Wind Energy Systems, Stockholm, Sweden, Sept. 1–24, 1982; Hydro-Quebec: Project Eole, 4-Mw Vertical Axis Aerogenerator, Montreal, 1985. 2. Ministry of Energy (Danish Energy Agency): Wind Energy in Denmark, Research and technological Development, 1990. 3. Friis, P., Large Scale Wind Turbines, Operating Hours and Energy Production, Elsam Project A/S. Internal Report, 1993. 4. Thomas Ackermann, Lennart Söder, Wind energy technology and current status: a review Renewable and Sustainable Energy Reviews, Volume 4, Issue 4, December 2000, Pages 315–374. 5. C. Soutis, Fibre reinforced composites in aircraft construction Progress in Aerospace Sciences, Volume 41, Issue 2, February 2005, Pages 143–151. 6. Isao Kimpara, Use of advanced composite materials in marine vehicles, Marine Structures, Volume 4, Issue 2, 1991, Pages 117–127. 7. L.M. Wyatt : Materials for MW sized aerogenerators Part 2. Materials characteristics Materials & Design, Volume 4, Issue 5, October–November 1983, Pages 880–884. 8. Christoph W. Kensche: Fatigue of composites for wind turbines, International Journal of Fatigue, Volume 28, Issue 10, October 2006, Pages 1363–1374. 9. Data from internal analysis by Owens Corning, 2010. 10. Mandell, J.F., Samborsky, D.D., and Cairns, D.S., ‘Fatigue of Composite Materials and Substructures for Wind Turbine Blades’, Contractor Report SAND2002-0771, Sandia National Laboratories, Albuquerque, NM 2002. 11. Manwell J.F, McGowan J.G, Rogers A.L., Wind Energy Explained, University of Massachussetts, Amherst, USA. 12. P.J. Hogg, A. Ahmadnia, F.J. Guild: The mechanical properties of non-crimped fabricbased composites, Composites, Volume 24, Issue 5, July 1993, Pages 423–432. 13. Michaeli/Huybrechts/Wegener, Dimensionieren mit Faserverbundkunststoffen, Hanser, 1995. 14. Generic IEC Class II blade construction – Owens Corning internal information 2010. 15. Det Norske Veritas, Guidelines for Design of Wind Turbines, DNV/Risoe, Copenhagen, Denmark, 2nd Edition. 16. Germanischer Lloyd, Guidelines for the Certification of Wind Turbines, Edition 2010, Hamburg, Germany, 2010]. 17. Locke J., Valencia U., ‘Design Studies for Twist Coupled Wind Turbine Blades’, SAND 2004-0522, Albuquerque/Wichita, USA]


Plate XI Parameters for the delamination interface model for materials NCF/LY3505 (* estimated) (Chapter 16).

Plate XII C-scans of impacted non-crimp fabric and prepreg specimens (30J) (Chapter 18).

Plate XIII Typical blade layout IEC class II 40m blade detailing the laminate constructions based on non-crimp fabric reinforcement materials (Chapter 21).


Plate XIV Blade deflecting under loads, coloured areas indicate highest stresses (Chapter 21).

Plate XV Nacelle cover under load (wind, snow). (Source M. Zvanik, OC Presentation CFA 2001, Tampa, FL). (Chapter 21).

Plate XVI Production in segments: Shell, spar cap, and root joint/ flanging reinforcements (Chapter 21).


22 Cost analysis in using non-crimp fabric composites in engineering applications P. SCHUBEL, University of Nottingham, UK

Abstract: This chapter describes the process for cost modelling non-crimp fabric (NCF) based composite structures. The chapter first looks at an overview of cost modelling techniques used in the composites industry and then focuses on the technical cost modelling (TCM) approach which is used in the case study. The case study presented investigates the cost centres for a 40 m wind turbine blade shell using NCF and a variety of manufacturing processes. Key words: technical cost modelling (TCM), non-crimp fabric, wind energy, wind turbine blades, cost analysis.

22.1

Introduction

This chapter describes the process for cost modelling a range of non-crimp fabric (NCF) based composite structures. The use of composite materials and type of processing method can almost always be seen as a trade-off between cost and performance. At one end of the scale are low-investment processes such as spray-up, which for example, compete favourably with wooden construction on a cost and performance basis. At the other end of the scale, there are aerospace processes involving considerable investment and full exploitation of composite advantages. High-performance materials and processing methods usually incur high costs and in some instances (e.g. satellite applications) this cost can be easily justified. Industries such as the automotive and wind energy industries are largely governed by the trade-off between cost and performance, which makes cost modelling an important aspect in advancing areas of design and manufacture. A simplistic view of this trade-off is shown in Fig. 22.1. This chapter focuses on the costs associated with the use of NCF in thermoset composites manufacture and uses a generic 40 m wind turbine blade as an example throughout the chapter. A wind turbine blade provides an excellent example to demonstrate technical cost modelling of NCF as they almost completely consist of unidirectional (UD) and multiaxial NCF. The 40 m blade being studied is a generic blade that consists of a two-part (upper and lower) aerofoil shell with a structural spar (main load-carrying member) (Fig. 22.2). This cost analysis will only be concerned with the manufacture of the two aerofoil shells.

494 © Woodhead Publishing Limited, 2011

Cost analysis in engineering applications

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22.1 The decision process relating part manufacture to cost effectiveness.

22.2 General shape of the shells and spar (including root joint).

22.2

Costing methodologies: current approaches

Cost modelling for composite components can be approached in a variety of ways, depending on what specific information is required. A good review of the various approaches currently exists (Bernet et al., 2002; Wakeman et al., 2005;


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Willden, 1997). Popular techniques include comparative techniques (Bader, 2002), process-orientated cost models (Gutowski, 1999; Choi, 2009; Kassapoglou, 1997), parametric cost models (Schubel, 2010; Ye et al., 2009) and process flow simulations (Barlow et al., 2002). These methods can provide a good guide to component cost, depending on your application and skill level. However, if all these seem daunting, then there is always experience based estimating! Comparative techniques are historically based and are therefore not suited to novel materials and processes. Process-orientated cost models are more adaptive, enable identification and quantification of part cost drivers and are sensitive to improvements in manufacturing processes (Bernet et al., 2002). However, they require in-depth knowledge of the manufacturing process and part geometry. Parametric models are flexible in their approach and allow easy manipulation of process and economic factors for sensitivity studies (Bernet et al., 2002). One drawback of parametric models is that each step in the manufacturing process operates independently from another, which typically results in underestimation of manufacturing cost. However, this problem is easily overcome by incorporating process flow simulations, which simulate the dynamics of a manufacturing process with a representation of the interactions between the different manufacturing operations. Benefits derived from implementing a process flow simulation model include the ability to predict cycle time and the capacity of the process (Bernet et al., 2002). The author's preferred method for cost modelling NCF based components is termed technical cost modelling (TCM), which is explained in more detail in Section 22.3 and is used in the case study (Section 22.4). This combined parametric and process flow simulation method is widely used throughout industry and allows good manipulation of data with fast analysis and moderate set-up time of the model. As a result, the TCM technique requires reasonable understanding of the manufacturing processes as it is an event-driven model. The TCM used in this chapter was created in Microsoft (MS) Excel™ with an MS Visual Basic™ analysis programme. The TCM approach is loosely based on the ACCEM model (LeBlanc et al., 1976) and has been comprehensively explained by Wakeman (Long, 2005). The most important thing to understand about cost modelling is that the results will only ever be as accurate as the input data.

22.3

Technical cost modelling

22.3.1 Overview TCM is a top-down approach designed to follow the logical progression of a process flow with a set of parametric equations for each level of detail available to the estimator. At the lowest levels, the cost of alternative designs and manufacturing methods can be estimated in order to make trade-offs. The TCM



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database provides labour standards for each type of material, as well as material prices, scrap allowances and learning curve factors. The results are an estimate of total component production costs. As mentioned earlier, TCM is event driven, which requires all relevant process steps to be defined for a particular component and manufacturing process. Therefore, the model is set up in discrete sections to reflect key areas/stages of manufacture, i.e. as costs are aggregated at higher levels, those components contributing most heavily to total product cost are isolated. It is from this basis that tooling, capital equipment, floor space and materials can be assigned. This is then coupled to overall variables such as plant capacity, program life, labour etc. (as illustrated in Fig. 22.1). Throughout a TCM analysis, all process parameters and production variables are assigned to cost centres such as: • • • • • • • •

Interest and depreciation Maintenance Utilities Floor space and building Tooling Labour Materials Transportation

This allows identification of cash-flow throughout the manufacturing process. It is the contribution of these cost centres which provide the total manufacturing cost. With this knowledge of the most prominent cost drivers, design engineers and managers can make cost-effective design decisions.

22.3.2 Setting global simulation variables One of the first steps to setting up a TCM for NCF processing is to define the global simulation variables that define the manufacturing plant and process. These will vary depending on the manufacturer and industry sector. However, general factors listed in Table 22.1 remain the same. Other factors such as insurance, selling costs, administration, transport, R&D etc are also part of the manufacturing cost. However, this information is not always readily available.

22.3.3 Part definition Detailed knowledge of the part geometry/complexity is not necessary for TCM. However, the more information you have on specifics, the more accurate the model inputs will be. Crucial inputs include part surface area – used throughout materials calculations and part perimeter – used in building utilisation calculations. As an example, Fig. 22.3 shows the relationship between part surface area and cost for the manufacture of the shells for a large wind turbine blade produced from


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Non-crimp fabric composites Table 22.1 Global simulation variables affecting all processes Variable

Units

Typical values (40 m blade)

Parts per annum Plant capacity volume Part programme lifetime Direct labour rate Indirect labour factor Interest rate on capital Building cost Machine residual value Capital equip depreciation period Installation cost Auxiliary equipment Equipment occupancy factor Insurance Energy costs

# # years £ / hour % % £ / m2 / year % years % % % % £ / hour

1500 260 3 11.09 100 7.50 72.90 5 10 10 15 200 0 0

22.3 Effect of part area on component cost for the shells of a large wind turbine blade manufactured using VI and NCF.

wind energy grade NCF and epoxy using the vacuum infusion (VI) process. The part area and perimeter for the generic 40 m blade shell was calculated as 270 m2 and 192 m, respectively. Once the costs have stabilised with increased production volumes or parts per annum (PPA), a clear linear relationship between cost and part area is seen for this



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case. This is partly due to the fact that materials costs make up a significant proportion of the total costs and, as mentioned earlier, part surface area is a direct driver for material costs in TCM.

22.3.4 Effect of production volume Production volume affects the cost and efficiency of manufacture for all components, irrespective of whether they are made from composites, steel, plastics etc. Typically, fixed costs such as capital equipment (Section 22.3.6) need to be seen as a trade-off against production volume. In respect to automated machines, such as ATL, AFP, braiding, winding etc, deposition rates typically dictate the capacity limits. NCFs are typically processed in low to medium volume production, where manual labour techniques are typically employed, as high-cost capital equipment would not be amortised over uneconomical volumes (Fig. 22.4). However, industry (in particular the wind energy industry) is realising the need for higher deposition rates through automation and are investigating novel ways of depositing and consolidating 300 mm to 1200 mm wide rolls of NCF in dry and prepreg forms. Current development areas include variations on the ATL principal.

22.4 Production volumes for thermoset and thermoplastic manufacturing adapted from (Manson et al., 2000).


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With reference to Fig. 22.3, it can be seen that there is an initial high component cost at low volumes (approximately 50 to 100 parts) due to the inability to amortise high fixed costs such as tooling and capital equipment associated with blade manufacture using NCF. The initial dramatic drop is then followed by a series of steps which stabilise with increased production volumes. The steps are a function of maximum capacity which can be a result of labour capacity, equipment capacity or as in this case, tooling capacity. Although the use of NCF improves the drapability and deposition rate of the reinforcement material over that of wovens, a bottleneck still appears due to the total tool usage time; this includes curing and bonding. This particular TCM has been setup to automatically include additional resources to meet the intended capacity. Therefore, at each step, there is a large capital cost that needs to be amortised at that particular production volume. As the production volume increases, resource sharing takes over and the cost of additional resources to meet production are easily amortised; leading to a stabilisation in production cost. At this point, costs such as labour and materials are the dominate drivers.

22.3.5 Materials In most composite materials processing, material costs make up a significant proportion of the overall component cost. Therefore, accurate reporting on material costs is crucial to cost modelling. The NCF and associated costs seen in Table 22.2 are given as examples and are current volume prices for early 2010. On average, it can be assumed that wovens cost 20% more than their NCF equivalent. The TCM process typically relates material costs to component surface area, requiring material costs to be stipulated as a function of surface area (£/m2). However, a common practice is to stipulate material costs as a function of weight (i.e. £/kg), which is easily interchanged by knowing the density of the material (Table 22.3). It is important to understand that materials do not just mean

Table 22.2 Material cost comparison: non-crimp fabric and woven Weight (g/m2)

Construction

0/90 0/90 +/−45 +/−45 0/−45/90/+45 0 0/90 0/90

Non-crimp fabric Non-crimp fabric Non-crimp fabric Non-crimp fabric Non-crimp fabric Non-crimp fabric Woven Woven

400 600 400 600 800 300 400 600

Cost E-glass (£/kg)

Carbon (£/kg)

3.90 2.77 4.20 3.08 3.38 2.94 4.66 3.26

43.70 43.40 40.80 40.30 50.40 46.70 45.10 44.90



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Table 22.3 Material information Variable

Units

Typical values (40 m blade)

Material ID

#

£/kg

Non-crimp fabric biaxial E-glass 600 (g/m2) prepreg 45% resin 2.68

% g/cc

7 1.8

Material description Cost Units Wastage Density

Table 22.4 Material costs Description

Unit cost

Gelcoat Non-crimp fabric Prepreg E-glass Non-crimp fabric Prepreg carbon Non-crimp fabric E-glass dry fabric Non-crimp fabric Carbon dry fabric Epoxy resin E-glass tows (2400 tex) Carbon tows (48K) E-glass prepreg tows Carbon prepreg tows Bond resin Release agent Solvent

6.71 2.68 18.80 1.31 16.84 2.50 0.74 11.41 1.00 23.49 6.04 0.50 0.10

£/kg £/kg £/kg £/kg £/kg £/kg £/kg £/kg £/kg £/kg £/kg £/m £/m

Waste 5% 1–7% 1–7% 10% 5% 10% 7% 7% 1% 1% 10% 5% 5%

reinforcement and resin in TCM. Included in this family are all consumables ranging from gelcoat, solvents, release agent, vacuum consumables etc. Basic material costs used in the current TCM model are shown in Table 22.4 and are obtained from a variety of sources. Materials and prices are based on the majority of sales within the wind turbine blade manufacturing industry for that particular type of product and are assumed to be ‘volume’ prices where available. Simple rule-of-mixtures costs are used for liquid composite moulding (LCM) processes such as VI and light resin transfer moulding (LRTM), with volume fraction and wastages taken into account. Wastage is set for each material individually. Within the materials specification in TCM it is also important to express a value for wastage/scrap for each material. This is typically represented as a percentage and is completely dependent on the material type, manufacturing process, etc. For example, it may be reasonable to assume +10% resin wastage for


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a VI process when you consider the amount of resin left in the infusion pot, infusion pipe, resin traps, breather membrane and flashing. In the case of NCF, even 30% waste is not uncommon, even with computer-optimised nesting. Materials costs are heavily influenced by volume of purchase, currency exchange rates, oil prices and global demand. The latter was clearly demonstrated in the carbon fibre market where demand outstripped supply during 2003 to 2008 as a result of significant uptake in commercial aircraft manufacture; resulting in up to 66% price increases (see Table 22.5). Prices appear to have stabilised with the introduction of additional carbon fibre production plants. In the example of a 40 m wind turbine blade shell manufactured using VI with a range of prices for NCF E-glass reinforcement (Fig. 22.5); the impact on total component cost is instantly observed. At the time of writing, the volume price on wind energy grade NCF was approximately £2/kg; however, this chart demonstrates the impact on cost that could be seen if any of the earlier mentioned

Table 22.5 Non-crimp fabric carbon biaxial cost between 2003 and 2010 Year

Material

Cost (£/kg)

2003 2008 2010

Carbon 12k biaxial non-crimp fabric Carbon 12k biaxial non-crimp fabric Carbon 12k biaxial non-crimp fabric

12 20 16

22.5 Effect of reinforcement cost on component cost for the shells of a large wind turbine blade manufactured using VI and NCF.



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influences such as currency exchange or global demand dramatically changed. Figure 22.5 also illustrates the cost difference in producing a 40 m blade from NCF (£2/kg) to an equivalent woven (£2.4/kg). The use of NCF in wind turbine blade manufacture has a 4.2% cost saving to the total blade shell cost when compared to an equivalent woven.

22.3.6 Capital equipment In all processing there is some element of capital equipment that needs to be considered and factored into the overall cost of the component. Capital equipment includes items seen in Table 22.6, although prices can vary dramatically depending on the scale of production. Presented are some guide costs for equipment related to large scale wind turbine blade manufacture. The elements of cost that need to be considered are detailed in Table 22.7 and clearly show that the initial purchase cost of the equipment is only a proportion of the true cost to the process. Table 22.6 Typical equipment costs for processing of large wind turbine blades using non-crimp fabric thermoset composites Equipment

Cost (£)

Overhead crane Gelcoat applicator Vacuum unit Tool heaters Freezer Adhesives applicator

500k 40k 20k 100k 100k 60k

Table 22.7 Capital equipment variable definitions Variable

Description

Purchase cost Residual value Parts per machine Length Width Occupancy factor Power usage Depreciation Auxiliary equipment cost Installation cost Reliability Machine lifetime Machine maintenance Tooling maintenance

£ % # Machine length (m) Machine width (m) Extra room taken up by auxiliary equipment (%) kW % % Percentage of purchase cost (%) Percentage time working (%) Effective machine lifetime (years) Factor used to account for machine maintenance cost Factor used to account for tooling maintenance cost


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Non-crimp fabric composites Table 22.8 Tooling variable definitions Variable

Description

Cost Parts per tool Tooling type Tooling lifetime

£ # Reference Number of hits lifetime

22.3.7 Tooling Tooling costs vary considerably depending on the size of the component, manufacturing method employed and annual production volumes (Table 22.8). These parameters dictate whether low-cost tools (composite) or high-cost tools (aluminium, chrome plated steel) are utilised. Tooling costs can make up a considerable proportion of the total component cost (especially for low volume production) and an understanding of how the tooling cost amortises is essential to cost efficient manufacturing. Using the example of a 40 m wind turbine blade shell mould set, composite tooling costs are around £1.2 million, which when amortised over a 100% utilisation factor for three years, the tooling cost accounts for 6.9% of the total blade cost. In contrast, if the same tooling was made from aluminium at a cost of approximately £2.1 million, then the tooling cost accounts for 11.5% of the total blade cost. It is this 4.6% cost difference between the two tooling types which means that all large-scale wind turbine blade shell tooling is produced from lowcost composite materials.

22.3.8 Cost modelling variables TCM is an event-driven costing tool and requires the manufacturing process to be detailed in such a way that it allows individual costs to be assigned to processes so that true and complete costing can be captured. There are different levels of detail that can be employed when setting a model and assigning events. This level of detail is influenced by many things, mainly information availability. A comprehensive list of cost modelling variables is shown in Table 22.9, which provides a good guide to the level of information required to implement a TCM.

22.4

Case study: 40 m wind turbine blade shell

22.4.1 Introduction The TCM approach detailed in Section 22.3 was used to compare the cost of manufacture of a 40 m wind turbine blade shell set with multiple manufacturing techniques. The six processes compared are; hand lay-up prepreg, VI, LRTM,



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Table 22.9 Cost modelling variables Variable

Acronym

Variable

Acronym

Parts per annum Plant capacity part program life part area part thickness Machine lifetime Tooling lifetime Labour cost Indirect labour factor Fringe factor Hours per day (labour) Hours per day (equipment) Days per year Interest rate Building cost Machine residual value Installation cost Auxiliary equipment Equipment occupancy factor Insurance Selling / general admin expense R&D allowance

PPA PLC PPL PAA PAT MAL TOL LAB IND FRL PDL PDE DPY INT BIL RES IST AUX EOF INS ADM RND

Materials Electricity cost Miscellaneous consumable

ELC MIS

Event step variables Cycle time Labour level Raw material Machine width Machine length Capital equipment cost Machine reliability Machine maintenance factor Tooling maintenance factor Utilities levels electricity Utilities levels misc. Tooling type Tooling lifetime (hits) Tooling cost Parts per tool Production shift Step yield

CYC LLV RAW MAW MAL CEC REL MMF TMF UTI UTM TOO TOL TOC PPT SHI STY

Table 22.10 Reinforcement types associated with the six manufacturing processes Manufacturing process

Reinforcement type

Hand lay prepreg Vacuum infusion (VI) Light transfer moulding (LRTM) Automated tape laying (ATL) Automated fibre placement (AFP) Overlay braiding

Non-crimp fabric Non-crimp fabric Non-crimp fabric Unidirectional tape Unidirectional tows Unidirectional tows

automated tape laying (ATL), automated fibre placement (AFP) and overlay braiding (Table 22.10). Of these manufacturing processes, NCF is used in the hand lay-up prepreg, VI and LRTM. Each event, therefore, has an assigned cycle time, labour usage, tooling and capital equipment. For all analyses presented, dedication of capital equipment is employed. No detailed consideration was given to plant layout in this work. An example of the primary events for the hand lay-up prepreg process is shown in Table 22.11. Cycle times have been established for the hand lay-up prepreg


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Table 22.11 Process cost model events for hand lay-up prepreg shell Event

Description

Materials

1 2 3 4 5 6 7 8 9 10 11 12

Prepare shell tool Gel coat Lay prepreg (shell) Apply vac bag consumables (shell) Check Vacuum Prepreg cure Remove consumables Trim shell Assembly-bond to spar Demould Store

Release agent gel coat Prepreg E-glass RFI consumables

Shell/spar bond resin

process and VI whilst the remaining processes have been determined experimentally. Processes such as ATL, braiding and AFP are highly automated and employ minimal manual labour.

22.4.2 Results The overall results for the six manufacturing processes for the shell structure are shown in Fig. 22.6. The results have been calculated over 2500 PPA to demonstrate individual blade cost as production increases.

22.6 Cost per part (shell) vs. production volume for the six manufacturing processes.



507

The cost of manufacture for the two halves of the shell is shown to fall rapidly up to a production level of around 400 units per annum for each of the six processes studied. After this, the cost stabilises up to 1000 units and generally plateaus thereafter. In each of the six cases studied, a step change can be observed roughly every 200 units as a result of multiple parallel tools being brought online to accommodate the annual capacity – this is a function of a set of predefined variables. The step changes are less pronounced as the PPA increase, due to the cost of additional tooling being distributed over an ever-increasing unit count. Over the six processes, the cost of shell manufacture generally ranges from £29 396 to £35 625 per part (based on 1500 PPA), with ATL and braiding making up these two extremities, respectively. The two benchmark systems (hand lay-up prepreg and VI) lay somewhat in the middle of these upper and lower extremities at £31 918 and £30 849 respectively. If the prepreg and liquid resin infusion (LRI) moulding techniques are isolated, then the two theoretical cost-effective manufacturing processes are ATL and LRTM respectively, with an average cost benefit of 8% over the benchmark systems. On a production run of 1500 per year, this equates to a potential cost saving of £3.8 million per annum. ATL and the hand lay-up prepreg (benchmark) both utilise a similar principal fabric system (prepreg) and therefore are a good comparison between automation and non-automation manufacture. Equipment depreciation costs (Fig. 22.7) from the purchase of the ATL facility are depreciated over ten years, as stated in Section 22.4.1, and rapidly off-set through the direct cost savings derived from reduced labour input and lower waste material levels. LRTM is best compared to the VI benchmark due to its similarity in using a form of LRI. Cost savings for LRTM are not fully recognised until after 300 PPA

22.7 Part cost of the shell split by process – based on 1500 PPA.


508


where additional tooling costs are absorbed by the production volume. An overall cost saving for LRTM verses VI is seen due to reduced cycle times and consumables (Fig. 22.7). Overlay braiding shows a 15% increase in cost over the benchmarks and exhibits exaggerated step changes in cost every 200 PPA on average. This is due to the increased manufacture time, additional processes (core manufacture) and high investment. AFP shows good potential; however, current material prices restrict its full cost effectiveness. This situation will change with increased uptake of the technology.

22.4.3 Cost breakdown A cost breakdown at three production levels for the shell production is shown in Fig. 22.8. In all cases, raw material costs are fixed and labour costs remain unchanged with production levels. The variables tend to be tooling and maintenance costs which are proportionately high at low production levels (230 PPA = 1 part per working day). Interest and depreciation is also a contributing factor for high investment processes such as ATL, braiding and AFP. However, in some cases this is off-set with high production volumes.

22.8 Split by process for the six case study processes at three volume levels.

22.4.4 Conclusions The methodology and results for a TCM exercise based around a 40 m wind turbine blade produced using NFC have been presented. Assumptions were made to create a general structure that could be applied to all scenarios. A comparison



509

of NCF-based manufacturing processes (hand lay-up prepreg, VI and LRTM) and automated fibre deposition processing (ATL, AFP and braiding) were compared and yielded results for a 40 m wind turbine blade shell production. Large blade shell production costs are predominantly influenced by labour costs and component area. If these two parameters are already fixed (i.e. an existing production site or set-up in a particularly high labour cost area), then results indicate that development should focus on reducing materials cost and reducing deposition time. It has been shown that NCF is a more cost-effective material over wovens for the case presented and the use of efficient NCF-based manufacturing processes such as LRTM warrants further investigation. Benefits to cost of manufacture through automation and tooling are clearly observed utilising this cost modelling exercise. However, significant downstream benefits can also be realised although not accounted for in this model. Benefits, such as improved quality control through automated processing and tighter dimensional tolerances have a direct impact on scrap rates.

22.5

Acknowledgements

The author would like to acknowledge funding from the Technology Strategy Board and other anonymous research projects for enabling the development of the TCM tools used in this case study. The author also wishes to thank anonymous consultants and manufacturers within the wind energy industry for providing valuable benchmark data in order to calibrate the TCM.

22.6

References

Bader, M. G. (2002) Selection of composite materials and manufacturing routes for costeffective performance. Composites: Part A, 33, 913–934. Barlow, D., Howe, C., Clayton, G. and Brouwer, S. (2002) Preliminary study on cost optimisation of aircraft composite structures applicable to liquid moulding technologies. Composite structures, 57. Bernet, N., Wakeman, M. D., Bourban, P. E. and Manson and J. A. E. (2002) An integrated cost and consolidation model for commingled yarn based composites. Composites: Part A, 33, 495–506. Choi, J. W. (2009) Architecture of a knowledge-based engineering system for weight and cost estimation for a composite airplane structures. Expert systems with applications, 36, 10828–10836. Gutowski, T. G. (ed.) (1999) Advanced composites manufacturing, New York, Wiley. Kassapoglou, C. (1997) Simultaneous cost and weight minimization of composite-stiffened panels under compression and shear. Composites: Part A, 28A, 419–435. Leblanc, D. J., Lorenzana, J., Kokawa, A., Bettner, T. and Timson, F. (1976) Advanced Composite Cost Estimating Manual. Volume I. NORTHROP CORP HAWTHORNE CA AIRCRAFT DIV, AFFDL-TR–76–87. Long, A. C. (ed.) (2005) Design and manufacture of textile composites, Cambridge England, Woodhead Publishing Limited.


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Manson, J. A. E., Wakeman, M. D. and Bernet, N. (2000) Composite processing and manufacturing – an overview. In Kelly, A. A. Z. C. (ed.). Oxford, Elsevier Science. Schubel, P. J. (2010) Technical Cost Modelling for a Generic 45m Wind Turbine Blade Produced by Vacuum Infusion (VI). Renewable Energy, 35, 183–189. Wakeman, M. D., Sunderland, P. W., Weibel, N., Vollmann, T. and Manson, J. A. E. (2005) Cost and implementation assessment illustrated through composites in the automotive industry – part I : methodology. Willden, K. (1997) Advanced technology composite fuselage manufacturing. National Aeronautics and Space Administration (NASA), report CR–4735. Ye, J., Zhang, B. and Haiming, Q. (2009) Cost estimates guide to manufacturing of composite waved beam. Materials and Design, 30, 452–458.


Index

[A1-B-A2]-HTA laminates, 341, 343, 350, 352 in-plane tensile modulus, 350 in-plane tensile strength, 352 normalised in-plane tensile modulus and strength, 343 [A1-(B/2)s -A2]2 -HTA laminates, 341, 344–5, 350–4 in-plane compression modulus, 351 in-plane compressive strength, 353 normalised in-plane compressive modulus and strength, 344 [A1-(B/2)s -A2]2 -HTS laminates, 345–6 in-plane shear modulus, 351 in-plane shear strength, 353 [A1-(B/2)s -A2]-HTS laminates normalised compressive strength after impact, 346 normalised in-plane shear modulus and strength, 345 normalised mode I energy release rate, 347 Abaqus Explicit, 157 ACCEM model, 496 acoustic emission, 280–3 advanced synchron weave fabric set-up, 24 illustration, 24 working principle, 24 aerospace applications aeronautic requirements, 443–5 C-scans of impacted non-crimp fabric and prepreg specimens, Plate XII residual compression strength and delaminated areas against impact energy, 444 application examples, 445–7 Airbus A380 rear pressure bulkhead, 445–6 Airbus A400M cargo door, 446–7 further applications on substructure level, 446–7 inside view of Airbus A400M cargo door, 446 non-crimp fabric carpet draping in Airbus A380 RPB production, 445 outside view of Airbus A400M cargo door, 447 future trends, 447–8 non-crimp fabric composites, 441–8 composite applications on Airbus A380, 442

evolution of composite structures within Airbus fleet, 442 Airbus A340, 441, 445 Airbus A380, 441 flap track, 447 rear pressure bulkhead, 445–6 Airbus A350 XWB, 441 Airbus A400M, 446–7 Airbus Industry Material Specifications (AIMS), 104 angle ply laminate, 314, 319 anisotropy, 193, 195, 201 ARAMIS strain-mapping system, 123 Ardrox Biopen P6F5, 192 ASTM D 1388–96, 392 ASTM D 5379/D 5379M – 93, 266 Audi A8, 462 automated analysis defects in fibre placement in non-crimp fabrics for composites, 103–14 motivation, 103–4 non-crimp fabric detailed picture, 107, 108 future trends, 111–14 blisters on different prepreg materials, 113 woven fabric area coverage via transmitted light device, 113 yarn width of warp yarns in a woven fabric, 112 gap and knitting errors, 109 motivation, 103–4 quality analysis by digital image analysis final results of different non-crimp fabrics, 110 grey value distribution histogram, 108 system, 106 working principle, 106–9 automated fibre placement (AFP), 505, 508 automated tape laying (ATL), 505, 507 automation, 71–2 automotive applications boot lid of Lamborghini Gallardo Spyder, 468–9 built-in FRP boot lid, 469 integrated construction, 469 car roof, roof carline and hybrid constructions at BMW Group, 466–8 BMW Hydrogen 7 side frame, 468

511 © Woodhead Publishing Limited, 2011

512

Index

CRP-roof industrial-scale manufacturing for BMW M3, 467 roof carline BMW M6, 466 roof of BMW M3, 467 future trends, 476–8 steel and textile production lines, 477 trends in fibre reinforced composite production, 477 multi-step preforming, 472–6 automobile underbody structure, 475–6 car roof segment, 474–5 preform centre, 473 production steps in preform centre, 474 roof segment preform, 475 underbody structure preforming, 476 non-crimp fabric composites, 461–79 cost distribution in preforming process, 465 production of parts of different complexity and quantity, 464 research and development, 469–76 Super Light Car, 462 single-step preforming, 470–2 feeding module for multi-axial warp-knitting machines, 471 folding gate with thread guides, 472 possible reinforcement yarn displacements, 472 ‘AutoPreforms,’ 474 average volume fraction, 405 B2 laminates, 279–83 barely visible impact damage, 300, 301, 304 bending hysteresis, 136 bi-axial carbon reinforcement fabrics, 364 bias direction, 265, 280, 312, 313, 314, 330 bias extension test, 117, 130, 392 biaxial fabrics, 118 biaxial non-crimp fabric composites deformability modelling, 144–62 modelling strategies, 148–9 energy-based kinematic mapping, 149–56 manufacture process statistical variation modelling, 156 modelling asymmetric shear behaviour, 150 modelling the effect of blank-holder, 155–6 predicted fibre patterns for nose cone, 156 fabric architecture behaviour on the shear and draping behaviour, 145–8 +/−45° NCF knitted with tricot stitch pattern, 146 NCF formed shape, 148 shear compliance curves for E-glass +/−45° tricot warp knitted fabric, 147 finite element modelling, 156–61 forming finite element modelling BHF effect on the formed shapes, 161 intra-ply slip modelling, 159 manufacture process statistical variation modelling, 160–1 meso-mechanical model representative cell, 158 modelling asymmetric shear behaviour, 157–8 modelling the effect of the blankholder, 160 out-of-plane bending stiffness modelling, 159–60

tows slip through the stitches in their axial direction, 159 future trends, 161–2 trellis shear force prediction vs shear angle behaviour using analytical models, 150–5 compaction model, 153 crossover model, 154 different mechanisms contributions, 154–5 forming set-up for Tay nose cone, 155 separate contributions to total normalised shear force of fabric stitch, 154 stitch crossover view, 152 unit cell stitch model, 151–3 unit tricot stitch, 151 biaxial warp-knitted non-crimp fabrics, 6–14 coursewise and non-coursewise weft insertion, 6 fabric set-up, 6 feeding module, 7–10 bobbin creels and cheese creel, 9 creel, 9 hook, needle and pin-hook system, 8 machine equipment, 10 weft carriage system, 7–8 weft thread transport system, 8–9 machine operation, 13–14 stitch types, 12, 13 pillar, tricot and plain stitch types, 13 take-up module, 12–13 cutting devise and vacuum cleaners, 13 fabric takeoff, 13 fabric wind-up, 13 warp-knitting module, 10–12, 13 knitting elements and walking needle concept, 10 loop formation process, 10–11 walking needle, 11 weft-thread sinkers, 12 yarn let-off, 12 working principle, 6–13 warp-knitting machine with biaxial weft insertion, 7 black-box modelling tool, 436 blisters, 113 BMW Hydrogen 7, 468 BMW M3, 467, 470 BMW M6, 466 bobbin threads, 69 Boltzmann model, 244–5 bonded tape non-crimp fabrics, 30–1 fabric set-up, 30 multiaxial bonded tape NCF, 31 working principle, 30–1 bonded thread non-crimp fabrics, 31–2 biaxial and multiaxial bonded thread NCF, 31 biaxial bonded thread non-crimp fabric production process, 32 fabric set-up, 31 working principle, 32 boundary conditions, 248–9, 375–83 braiding technology, 69 Brinkman equations, 247, 249–50 bulk moulding components (BMC), 462 BVID see barely visible impact damage


Index CAI see compression after impact carbon-epoxy cross-ply laminate, 325–6 carbon-epoxy NCF composites, 330 carbon-epoxy plain weave composite, 326 carbon fibre composites, 420 carbon fibre-reinforced plastic laminates, 335 carbon fibre reinforced polymer composites (CFRP), 449 carbon fibres, 50, 57, 104 carbon sewing threads, 69 carriage, 54 CEC project Falcon, 395 Celper, 337 Chevrolet, 462 Chiu model, 350 Chorin projection method, 250 Christensen’s self-consistent approach, 407 clamping system, 128 classical laminate theory (CLT), 278–9, 297, 324–5, 387, 403, 411, 413, 420, 436 cohesive zone interface, 397 ‘compaction and stretch’ (C&S), 458 compaction model, 153 Composite Cylinder Assemblage, 405 composites fibre placement defects automated analysis in non-crimp fabrics, 103–14 future trends, 111–14 motivation, 103–4 non-crimp fabric quality analysis by digital image analysis, 106–11 non-crimp fabrics quality characteristics, 104–6 non-crimp fabric preforms structural stitching, 67–82 applications and future trends, 81–2 quality aspects for structural stitching, 74–81 stitching technology and sewing machines, 70–4 threads for structural stitching technology, 68–70 non-crimp fabrics production, 3–37 3-D woven and non-interlaced non-crimp fabric, 27–30 fixation by adhesion, 30–3 future trends, 35–7 non-crimp fabrics overview, 4 non-crimp woven fabrics, 23–7 production technologies comparison, 33–4 warp-knitted non-crimp fabric, 5–22 weft-knitted non-crimp fabric, 22–3 compression after impact, 302, 336, 346, 354 core spun yarns, 69 Cos Law, 279 cost analysis 40 m wind turbine blade shell case study, 504–9 cost breakdown, 508 cost per part vs production volume, 506 part cost of shell split by process, 507 process cost model events for hand lay-up prepreg shell, 506 reinforcement types associated with six manufacturing process, 505 split by process for the six case study processes at three volume levels, 508

513

non-crimp fabric composites in engineering applications, 494–509 costing methodologies, 495–6 decision process relating part manufacture to cost effectiveness, 495 general shape of shells and spar, 495 technical cost modelling, 496–504 capital equipment, 503–4 cost modelling variables, 504, 505 effect of production volume, 499–500 materials, 500–3 part definition, 497–9 technical cost modelling (TCM) setting global simulation variables, 497, 498 tooling, 504 crack density, 315–17 crack-opening displacement, 295 crochet technology, 69 cross direction, 265, 282 crossover model, 154 Culimeta, 69 3D FE Hom-0°, 416, 419 ‘3D FE’ model, 415, 416, 436 damage accumulation, 372–83 boundary conditions, 375–83 experimental observations, 372–5 damage development, 314–19 damage progression impacted NCF composites, 300–7 BVID and VID impacted sandwich face sheet laminates, 301 BVID in a sandwich face sheet laminate, 301 dashed area polished in the thickness direction, 303 delaminations in a NCF laminate with BVID, 302 impact damage formation, 300–2 impact damage tolerance, 302–7 longitudinal strain close to failure, 307 monolithic CAL panel, 304 in-plane loading, 290–9 crack-opening displacement schematic, 295 double crack, 296 half crack running through one 90° fibre bundle, 294 in-plane compressive failure, 296–9 intralaminar matrix tensile cracks, 291 longitudinal cracks, 295 NCF cross-ply laminate cross-section, 291 quasi-isotropic specimens loaded to compressive failure, 298 tensile loading, 290–6 whole crack, 292 whole cracks, half cracks and double cracks densities, 293 kink bands 5° ply of a 5° off-axis loaded QI specimen, 299 detailed view, 299 formation in a 45° layer, 305 impacted skin of panel with BVID, 305 monolithic CAI panel micrograph, 306 outer 45° ply of monolithic CAI panel, 306 non-crimp fabric composites, 289–308


514

Index

Darcy’s Law, 168, 216, 242–3, 246, 389 deformability bending, 136–9, 140 diagrams, 137 heavy carbon tows bending rigidity, 139 rigidity, 137 biaxial tension, 128–32, 140 biaxial tensile tester and sample clamping, 129 equipment and samples, 128 fabric compression diagram, 131 fabrics tension, 130 simplified models validity, 132 tension diagrams, 128–32 compression, 132–6, 140 first compressive cycle, 135 nesting coefficients, 136 nesting effect in the fabrics, 136 test results, 133–4, 135 trends in the compressive behaviour, 134–5 modelling in biaxial non-crimp fabric composites, 144–62 energy-based kinematic mapping, 149–56 fabric architecture behaviour on the shear and non-crimp fabrics draping behaviour, 145–8 finite element modelling, 156–61 future trends, 161–2 modelling strategies for non-crimp fabric forming, 148–9 non-crimp fabric composites manufacture, 117–40 non-crimp fabric, face and back samples, 120 non-crimp fabric parameters, 119 tests summary, 120 shear, 118, 120–8, 139–40 diagrams, 124–8 difference of shear angle of fabric B2 and frame shear angle, Plate I picture frame, 121 picture frame test, 121–3 SC, ST, and SS tests diagrams, 124 shear force tests diagram, 127 two fabrics shear diagrams comparison, 126 delaminations, 289–307, 317, 320, 323, 331–2, 347 DIN 65148, 62 Dirichlet boundary conditions, 390 double-cantilever beam (DCB) tests, 346–7, 398, 399 double cracks, 295–6 90° fibre bundle, 296 drape forming, 452 dry friction, 392 E-glass fibre, 325 EN 13427, 43 EN 13473, 42 EN 13427-1, 44 EN 13473-1, 43 abbreviations for material type, 44 code letter for binding system type, 45 End Notched Flexure test, 398 engineered fabrics, 171 EP 1 352 118 B1, 63–4 Epikote 828 LV, 265

Epikure DX 6514, 265 European standard EN 13473, 85 failure index, 370, 371–2, 379–80 FALCOM project, 184, 187, 209 fatigue appendix, 333–4 biaxial carbon fibre NCF, 334 NCF internal geometry characteristics, 334 carbon-epoxy NCF composite and carbonepoxy twill weave composite after tensile fatigue fibre direction for 103, 104, 105 and 2.5 × 105 cycles, 318 fibre direction for 104, 105 and 2.5 × 105 cycles, 319 damage development, 314–19 crack density, 316 transverse matrix cracks in a biaxial carbon-epoxy NCF composite, 316 fatigue life curves bias direction of a twill weave carbon fibre-epoxy composite, 313 different off-axis angles of cross-ply composites, 327 different orientations of a ±45° carbon epoxy NCF composite, 329 fibre direction of twill weave carbon fibre-epoxy composite, 313 fibre directions of carbon-epoxy non-crimp fabric composite, 312 matrix dominated directions, 312 room temperature fatigue life curves for unidirectional carbon-epoxy composite, 326 influence of fibre orientation, 324–30 normalised fatigue stress vs. number of cycles to failure, 330 tensile fatigue tests results, 328 variation of elastic constants, 325 non-crimp fabric composites, 310–34 fatigue life, 311–14 open questions, 332 post-fatigue residual properties, 330–2 post-fatigue and intact compressive strength, 331 stiffness evolution, 319–24 average stiffness evolution, 323 fatigue process on the normalised composite stiffness, 320 glass fibre-reinforced polymer laminates normalised stiffness evolution, 321 quasi-isotropic and ±45°, 322 static stiffness evolution, 324 stiffness decrease, 320 fatigue life, 311–14 FETex, 337 fibre distortion, 92 fibre placement defects automated analysis in non-crimp fabrics for composites, 103–14 future trends, 111–14 motivation, 103–4 non-crimp fabric quality analysis by digital image analysis, 106–11 non-crimp fabrics quality characteristics, 104–6


Index

515

fibre sizing, 70 fibre-tow spacing, 218 fibre tow waviness, 220, 230, 234 filled markers, 175 finite difference, 245 finite element analysis non-crimp fabric composites, 360–83 damage accumulation, 372–83 elastic analysis, 369–72 representative volume element, 363–9 finite element method, 148 finite element model, 369–72 damage initiation and stiffness response, 370–2 peculiarities, 370 finite element simulation, 149, 245 finite volume simulation, 245 fisheye openings, 107, 158, 458 FlowTex, 246, 337 fluid flow models, 246–8 fold-wound non-crimp fabrics, 32–3 fabric set-up, 32 fold-winding system, 33 working principle, 33 Formula 1, 462 free nodes, 431 frictional energy, 155 Froude number, 243

infusion technology, 483–4 injection flow rate, 224 injection pressure, 223 Instron 1196, 266 Instron 4467, 121, 132 Instron 4505, 265–6 Integrated Tool for Simulation of Textile Composites, 337 inter-tow sliding, 390 interactive failure criteria, 433 interlaminar cracks see delaminations intermediate preforms, 450, 453 INTEX, 464 intra-ply slip (IPS), 458 intralaminar cracks, 289–91 double cracks, 295–6 half-cracks, 294–5 longitudinal cracks, 295 schematic, 291 whole cracks, 291–4 ISO 527–4, 265–6 ISO 3374, 46, 47 ISO 4921, 47 ISO 14130, 266 ISO/DIS 1268-1, 45 iso-strain model, 419 ITOOL see Integrated Tool for Simulation of Textile Composites

Gebart’s equation, 198 GLARE, 443 glass fibre composites, 420 glass fibre mat thermoplastics (GMT), 462 glass fibre NCF composites, 311, 315 glass fibre reinforced plastics (GFRP), 461–2 ‘global criteria,’ 433 global delamination, 320 global permeability, 237 ‘Growian,’ 481 gRVE, 363, 366, 375

Jeeves minimisation method, 150

half-cracks, 294–5 crack-opening displacement, 295 densities, 293 one 90° fibre bundle, 294 Halpin-Tsai expressions, 407–10 hand lay-up prepreg, 504 process cost model events, 506 Hashin’s CCA model, 407–10 Hexcel, 171 Hexcel Fabrics, 59 Hexcel-patent, 59–61 Hooke method, 150 Hooke’s law, 387 impact damage formation, 300–2 tolerance, 302–7 delamination growth, 303–4 kinking of fibre tows, 304–7 in-plane buckling, 457 in-plane compressive failure, 296–9 in-plane dimension, 218 in-plane permeability, 217 in-plane permeability values, 222, 223, 224 in-plane shear test, 266 in-situ strength, 426

Karl Mayer Textilmaschinenfabrik GmbH, 51, 54, 57 Kawabata Evaluation System (KES-F), 127 kinematic mapping methods, 148 kink bands, 298–9, 304–7, 421 5° ply of a 5° off-axis loaded QI specimen, 299 detailed view, 299 formation in a 45° layer, 305 impacted skin of panel with BVID, 305 monolithic CAI panel micrograph, 306 outer 45° ply of monolithic CAI panel, 306 knitted web, 86 Kozeny–Carman equation, 188, 197 Lamborghini Gallardo Spyder, 468–9 laminate thickness, 342–3 LamTex, 337 Lancia Lamda, 461 Laplace equation, 390 lapping diagram, 88 LCM see liquid composite moulding Leicester notation, 88 Leno weave, 25–6 fabric set-up, 25 uniaxial and biaxial reinforcement, 25 working principle, 25–6 technique, 26 LIBA Maschinenfabrik GmbH, Naila, 47, 52 LIBA Max 3 CNC, 47 clamping sequence, 53 computer-controlled weft-insertion system, 48 taper-layer system, 52 transport-chain, 52 light resin transfer moulding (LRTM), 501, 504, 507–8 LIMS, 242, 389


516

Index

liquid composite moulding (LCM), 166, 216, 242, 449, 501, 507 liquid resin infusion (LRI), 166 flow process, 389–90 local delamination, 314, 315, 320, 324 local permeability, 237–8, 249 longitudinal cracks, 295 longitudinal intralaminar cracks, 289 loop formation process, 10–11 illustration, 11 LY3505 resin, 399 machine direction (MD), 265, 280 Marie Curie Fellowship, 204 master surface, 397 match mould forming, 452 matrix cracks see intralaminar cracks mechanically representative volume (mRVE), 363–4 MeshTex, 337 meso-analysis, 360–83 see also finite element analysis meso models, 361–2, 370 see also finite element model meso scale modelling, 383 see also finite element analysis mesoelements, 405, 417 micro-level flow phenomenon, 173 microscale homogenisation, 405 Mixed Mode Bending (MMB) test, 398 MMF see multiaxial multiply fabrics mode I energy release rate, 346–7 modified Tresca criterion, 427, 428 modified von Mises type of criteria, 430 Monte Carlo method, 156 Monza, 462 multi-ply carbon reinforcement fabrics, 364 multiaxial multiply fabrics, 85, 263 failure pattern, 269 mechanical properties, 274–9 reinforced epoxy composites in-plane shear properties, 272 interlaminar shear strength, 274 tensile properties, 267 specifications, 264 tensile stress–strain curves of laminates, 268 multiaxial warp-knitted non-crimp fabric, 14–20 coursewise and non-coursewise weft insertion, 14 fabric-set-up, 14–15 schematic set-up with non-coursewise weft insertion, 15 feeding module, 17–20 creel, 19 machine equipment, 20 pin-pin, needle-field and clamping system, 18 spreading device with electrodes, 20 stationary and mobile weft-insertion portal, 18 weft carriage system, 17–18 weft thread transport system, 18–19 take-up module, 20 warp-knitting module, 20 working principle, 15–17 coursewise multiaxial warp-knitting machine, 16

non-coursewise multiaxial warp-knitting machine, 17 NaSt3DGP, 250–1 Navier-Stokes equations, 244–6 see also NaSt3DGP NCF see non-crimp fabrics NEDO, 465 nesting behaviour, 97 Neumann boundary conditions, 390 Newtonian incompressible liquid, 389–90 Newton–Raphson type solution, 387 Newton’s second law of motion, 387 NH90, 449 non-crimp fabric composites see also structurally stitched NCFcomposites aerospace applications, 441–8 aeronautic requirements, 443–5 application examples, 445–7 future trends, 447–8 automotive applications, 461–79 future trends, 476–8 research and development, 469–76 average transverse strain in bundle at 1% applied strain, 432 dependent on its geometry, 433 boundary conditions for a damaged composite, 375–83 constructing BC for the balanced laminate, 378 drop of secant moduli and failure index, 380 elementary ply post-critical behaviour, 380–3 local stress density and distribution, 377 modelling cracks on the meso scale, 377–80 normalised secant moduli in tensile tests, 383 out-of plane displacement, Plate IV ply deformation, 376 shear diagrams from two tensile tests, 382 test problem, 376–7 transverse stress distribution, 380 unit cell and the contours of the unit cells, 378 compressive strength in nominal bundle direction, 421–4 fibre bundle waviness and kinking failure, 421 linear fit to experimental values compared with prediction from criterion, 424 off-axis QI-laminate test specimens failed in compression, 423 stresses in 0°-plies at specimen failure, 423 cost analysis of engineering applications, 494–509 case study, 504–9 costing methodologies, 495–6 technical cost modelling, 496–504 damage accumulation, 372–83 experimental observations, 372–5 tensile diagrams, 374 tensile tests in longitudinal direction, 373 damage development in B2 laminates, 279–83 acoustic emission, 280–3


Index AE counts, event energy, cumulative energy and stress–strain curve, 281 strain levels based on AE results, 283 damage initiation in non-sheared and sheared materials, 285–7 initial damage investigation, 286 damage progression, 289–308 impacted NCF composites, 300–7 in-plane loading, 290–9 drape, stress and impact behaviour modelling, 386–400 finite element method, 386–7 finite element methods for infusion analysis, 389–90 draping analysis and finite element simulation, 390–4 finite element drape simulation, Plate VII kinematic and finite element simulation results, Plate VI kinematic drape algorithm solution scheme, 391 principal deformations modes in bi-axial fabric, 390 shear angle distribution in pitch horn, Plate V testing methods for fabric drape properties, 393 two stacked plies and constitutive laws for NCF, 392 effect of stitching on the mechanical properties and damage, 360–83 internal composite geometry models, 361–2 elastic analysis, 369–72 artificial stress concentration, 370 finite element model, 369–72 stiffness and damage features, 371 stress exposure factor, 371 fatigue, 310–34 appendix, 333–4 damage development, 314–19 fatigue life, 311–14 influence of fibre orientation, 324–30 open questions, 332 post-fatigue residual properties, 330–2 stiffness evolution, 319–24 fibre arrangements loaded in tension and compression transverse failure strain initiation, 430 transverse failure stress initiation, 430 finite element model and FE mesh, Plate III impact and failure, 396–400 equivalent NCF/LY305 ply properties, 399 inter-ply delamination model, 398 parameters for delamination interface for materials NCF/LY3505, 400, Plate XI test and simulation results for DCB tests, 399 infusion simulation, 394 different infusion strategies and contours of filling times, Plate IX model zones for thickness and permeability variations, Plate VIII laminate analysis and finite element stiffness, 387–9 Hooke’s law for orthotropic ply and fibre axis system, 388

517

multi-layer element and element stiffness matrix, 389 laminate hierarchical structure, 403 layer representation, 414 materials and composite production, 264–5 multi-axial multi-ply carbon fabric specifications, 264 mechanical properties, 266–74 failure pattern, 269 in-plane shear properties, 271–3 interlaminar shear strength, 273–4 MMF in-plane shear properties, 272 MMF interlaminar shear strength, 274 MMF tensile properties, 267 shear Iosipesku test, 271 short beam shear test specimens after testing, 273 tensile properties, 266–71 tensile stress–strain curves, 268 mechanical properties based on sheared multiaxial multiply fabrics, 274–9 failure patterns, 277 ply angles, fibre volume fractions and tensile properties, 276 sheared specimens in shear frame, 274 tensile properties, 275 representative volume element, 363–9 NCF plane geometry and unit cell geometrical model, 365 non-matching skewed UC’s, 365 non-matching unit cells of two adjacent layers, 366 non-periodical nature of the damaged composite, 367 rectangular unit cell, 368 representative capability with the classical periodic boundary conditions, 368 representative volume definition, 363–9 required inputs and obtained outputs from ‘black box’ modelling tool, 404 simplified geometrical models for mesostructure, 414–20 boundary conditions applied to surface of representative volume elements, 419 comparative analysis of stiffness models, 417–20 in-plane stiffness, 416–17 material properties used in numerical analysis, 418 mesoscale structure, 415 stiffness of carbon fibre non-crimp fabric composite, 419, 420 stiffness and failure, 394–5 mechanical and failure data for single ply, 395 notation for elementary ply, 395 test and analysis results for failure, Plate X stiffness and strength, 263–87 materials and composite production, 264–5 test procedures, 265–6 stiffness and strength modelling, 402–36 stiffness models, 405–20 axial modulus and major Poisson’s ratio for NCF cross-ply laminate, 413 axial modulus and major Poisson’s ratio for NCF quasi-isotropic laminate, 413


518

Index

curved beam model with fixed fibre tow ends, 412 effective longitudinal modulus of curved tows, 411–14 fibre and matrix properties used in micromechanical study, 408 longitudinal modulus, 409 microscale modelling of elastic properties of fibre tows, 407–10 Poisson’s ratio, 410 possible workflow of multiscale analysis, 406 reduced axial modulus due to tow waviness, 411 repeatable unit cells, 408 sensitivity of knockdown factor, 412 shear moduli, 410 transverse modulus, 409 strength models, 420–35 strength transverse to fibre direction, 424–35 average strain in NCF composite bundle, 431–3 failure criteria for bundle mesostructures, 433–5 hexagonal and square fibre arrangement, 429 mesogeometry simplification, 432 micro-meso approach for transverse matrix crack initiation, 424–6 microscale strength modelling, 426–31 model used for parametric study of interface distortion, 432 parameters as determined by uniaxial tension and compression tests, 427 test procedures, 265–6 in-plane shear test, 266 short beam shear test, 266 tensile test, 265–6 textile preforms deformability, 117–40 bending, 136–9, 140 biaxial tension, 128–32, 140 compression, 132–6, 140 shear, 118, 120–8, 139–40 variability in permeability of composite reinforcements, 216–39 future trends, 239 material characterisation, 217–22 modelling and simulation, 233–8 permeability measurement, 222–33 wind turbines, 481–92 development in wind energy, 483–91 future trends, 492 materials used in nacelle construction, 491–2 X-ray radiography, 283–5 B2 specimens subjected to tensile loading, 284 non-crimp fabric preforms, 492 analysis for helicopter applications, 449–60 automated lay-up machine, 451 defect analysis, 456–8 limit fibre path of preform on a helicopter frame, 458 terminology of defects, 457 deformation mechanism during preforming, 454–6 classification of deformation mechanism, 455 stitch yarns deformations, 456

future trends, 458–60 applications and main benefits, 459 NCF tailored reinforcements diaphragm forming, 452 drape forming, 453 stretch forming, 453 non-crimp fabric process chain with quality gates, 451 permeability, 166–209 deformation and permeability, 196–208 experimental permeability results, 168–87 geometrical effects, 187–96 nomenclature, 214–15 techniques for non-crimp fabrics, 449–54 final preform, 453–4 process chain, 450–1 tailored reinforcements, 451–2 technical principle, 450 types of forming methods, 452–3 non-crimp fabrics see also specific non-crimp fabrics 3-D woven and non-interlaced non-crimp fabric, 27–30 2D, 3D and non-interlacing weaving, 29 fabric set-up, 28–9 orthogonal, multilayer, and angle-interlock fabric structures, 28 production technologies categorisation, 28 working principle, 29–30 areal weight estimation, 45–7 necessary characteristics and resolution of used balance according to ISO 3374, 47 suggested method for cutting out fabric specimens, 46 automated analysis of fibre placement defects for composites, 103–14 curvature in knitting rows, 111 detailed picture, 107, 108 exemplary defects, 105 future trends, 111–14 gap and knitting errors, 109 motivation, 103–4 quality analysis by digital image analysis, 106–11 quality characteristics, 104–6 bonding patterns, 47, 48 commonly used bonding patterns, 48 carbon biaxial cost between 2003 and 2010, 502 computer-controlled weft-insertion system, 47–50 patented in DE 19726831 C2, 49 transport chain and layer-carriage, 50 deformability modelling, 144–62 energy-based kinematic mapping, 149–56 finite element modelling, 156–61 future trends, 161–2 modelling strategies for non-crimp fabric forming, 148–9 draping behaviour and fabric architecture behaviour on the shear, 145–8 +/−45° NCF knitted with tricot stitch pattern, 146 NCF formed shape, 148 shear compliance curves for E-glass +/−45° tricot warp knitted fabric, 147


Index EN 13473-1 abbreviations for material type, 44 code letter for binding system type, 45 EP 2003232 A1 carriage, gripper and tape movements during a lay-up sequence, 57 offline spread tape placing sequence into the transport-chains, 58 online tow spreading system, 56 principle of combined creel and spreading-unit, 56 existing machines outstanding patents, 47–59 fixation by adhesion, 30–3 bonded tape, 30–1 bonded thread, 31–2 fold-wound, 32–3 ‘Hexcel-patent’ – EP 0972102 B1, 59–61 basic architecture of modern machines similar to Hexcel concept, 61 overview of the range of the patent, 60 important terms and definitions, 43–5 data-block 1, 44 data-block 2, 44–5 data-block 3, 45 designation system for multiaxial non-crimp fabrics [EN 13427-1], 44 internal geometry characteristics, 334 layer orientation definition, 45, 46 ISO/DIS 1268-1/EN 13473-1, 46 LIBA Max 3 CNC clamping sequence, 53 computer-controlled weft-insertion system, 48 taper-layer system, 52 transport-chain, 52 materials and stitching configurations, 337–9 modelling of permeability for composites, 242–58 experimental validation, 251–3 influence of shear, 256–7 numerical simulation, 246–51 parametric study, 253–6 new weft-thread transport systems, 50–4, 55 Karl Mayer type clamping system for spreading tapes, 51 principle for transport belts use between the warping needles [DE19852281 C2], 55 online tow spreading and feeding systems, 54–9 device to feed fibrous bands into a knitting machine [DE102005008705 B3], 59 overview, 4 preform process chain with quality gates, 451 preforming analysis for helicopter applications, 449–60 deformation mechanism during preforming, 454–6 future trends, 458–60 preform techniques, 449–54 preforming defect analysis, 456–8 preforms structural stitching for composites, 67–82 applications and future trends, 81–2 quality aspects for structural stitching, 74–81 stitching technology and sewing machines, 70–4

519

threads for structural stitching technology, 68–70 product patents, 61–4 adhesive immobilisation on the surface of semifinished textile products (DE 102008004112 A1), 64–5 integrated manufacturing process for stringer stiffened panels (DE 102005052573 A1), 61–3 integrated production process, 62 non crimp fabrics stitched together using a fusible thread (EP 1 352 118 B1), 63–4 test specimen preparation, 63 textiles adjustment at the rotor blade mould vertical surfaces, 64 production for composites, 3–37 future trends, 35–7 preforming technologies, 36 production methods classification and standardisation, 42–7 classification, 43 production technologies comparison, 33–4 classification, 34 realisable productivity and complexity, 34 production technologies standardisation, 42–65 quality analysis by digital image analysis final results of different non-crimp fabrics, 110 grey value distribution histogram, 108 system, 106 working principle, 106–9 understanding and modelling stitching effect on geometry, 84–101 change in the geometry after shearing, 98–100 fibres distortions in the plies, 92–8 fibrous plies general parameters, 85–6 non-crimp fabric geometrical model, 100 stitching geometry, 86–92 warp-knitted, 5–22 biaxial, 6–14 coursewise and non-coursewise characteristics, 5 multiaxial, 14–20 spacer, 21–2 weft-knitted, 22–3 biaxial and multiaxial weft-knitted non-crimp fabric, 22 fabric set-up, 22–3 multilayer weft-knitted non-crimp fabric structures, 23 working principle, 23 woven fabrics, 23–7 advanced synchron weave, 24 Leno weave, 25–6 Tape weave, 26–7 non-periodicity, 368–9 noobing, 28 normal loading, 418 off-fibre tests, 372–3 oil price shock, 481 open markers, 175 overhang test, 392 overlay braiding, 505, 508


520

Index

PAM-CRASH, 157, 158 PAM-QUIKFORM, 391–2, 395 PAM-RTM, 242, 389 partial iso-strain model, 417, 419 patent DE 1020055052573 A1, 61–3 patent DE 102005052573 A1, 61–3 patent DE 102008004112 A1, 64–5 patent DE 102005008705 B3, 59 patent DE 10214140 B4, 52 patent DE 19726831 C2, 47–50, 49 patent DE 19852281 C2, 55 patent EP 1 352 118 B1, 63–4 patent EP 2003232 A1 carriage, gripper and tape movements during a lay-up sequence, 57 offline spread tape placing sequence into the transport-chains, 58 online tow spreading system, 56 principle of combined creel and spreadingunit, 56 patent EP 0972102 B1, 59–61 patent EP 1512784 B1, 57 permeability characteristics and results biaxial, triaxial, quadriaxial and multiaxial fabrics and transverse permeability experiments, 183 biaxial carbon fibre fabrics, 177–8 biaxial glass fibre fabrics, 179–80 in-plane permeability experiments, 176–82 triaxial, quadriaxial, and multiaxial fabrics, 181–2 uniaxial fabrics, 176 and deformation, 196–208 compression, 197–8, 199–200 fitted values for bundle radius, 198 relation between permeability and fibre content, 199–200 experimental permeability results, 168–87 experimental validation, 251–3 bi-axial vs. quadri-axial non-crimp fabric, 252 sheared bi-axial non-crimp fabric models, 253 tensor components, 252 geometrical effects, 187–96 influence of shear, 256–7 permeability values and angle of principal direction, 256 principal direction as function of shear angle, 257 material characterisation, 217–22 angle χ distribution between fibre and fabric weft direction, 219 fabric superficial density, average ratio, and standard deviation of fibre angles, 220 gaps configuration, 221 local superficial densities distributions, 219 stitching thread on fibre configuration, 221 unit cell, 218 measurement, 171, 173–87, 222–33 base configuration properties of Devold NCF, 186 distribution of angle θ between fabric weft and principal flow direction, 229 distribution of principal in-plane permeability value K1, 228

distribution of principal in-plane permeability value K2, 228 distribution of principal through-thickness permeability value K3, 231 experiment results for three fabric layers, 225 fabric unsaturated ratio over saturated permeability, 185 flow experiment results for six fabric layers, 230 flow front shape at a given injection time, 225 glass and carbon NCF permeability, 174 illustration, 173 methods and errors, 222–4 principal in-plane average values and coefficients of variation, 226–7 results, 224–33 through-thickness permeability values, 232 measuring technologies, 168–71, 172 measuring methods main characteristics, 172 NCF internal geometry at multiple scales, 168 transverse permeability measuring device cross-section, 171 typical line, radial and transverse permeability measuring equipment, 170 modelling and simulation, 233–8 coefficients of variation of global permeability, 237 distances between axes of wavy fibre tows, 234 function of the co-ordinates for a set of example parameters, 235 simulated flow front shapes in radial injection, 236 modelling in non-crimp fabrics for composites, 242–58 geometrical properties, 245 prediction of textile permeability, 246 undeformed quadri-axial and bi-axial fabric geometrical data, 244 multi-ply vs multiple layers, 187–91 biaxial and quadriaxial fabric crosssection, 188 biaxial NCF microscopy image, 191 permeabilities at 55% fibre content equivalent permeabilty, 189 nomenclature, 214–15 non-crimp fabric preforms, 166–209 numerical simulation, 246–51 boundary conditions, 248–9 Brinkman equations solution, 249–50 computation flow chart, 248 fluid flow models, 246–8 implementation, 250–1 principal direction, 251 parametric study, 253–6 perturbed quadri-axial model, 254–5 WiseTex model of biaxial and quadriaxial non-crimp fabric, Plate II shear deformation, 198, 201–8 effect on Tricot stitch patterns, 202–3 fabrics permeability vs shear, 205 orientation angle, 207 permeability anisotropy of sheared fabric vs shear relation, 206


Index stitching influence, 191–6 carbon and glass fibre based uniaxial and triaxial fabrics, 195 experimental set-up to track the flow front in detail, 192 fabrics anisotropy vs with even and uneven number of plies, 194 identifiers of Devold NCF variants, 196 polyol-Ardrox biopen flow front, 193 variability in non-crimp fabric composite reinforcements, 216–39 future trends, 239 permeability tensor, 242–3, 251 PETSc library, 250 physically representative volume (pRVE), 364 picture frame test, 117, 121–3, 392 pin-jointed net (PJN), 149, 150 pitch lengths, 339 plastic fibre microbuckling, 421 plastic shear instability, 421 ply deformation, 376 Poisson coefficient, 381 Poisson’s ratio, 407 polyol, 192 porosity, 223 Porsche, 462 power law, 133 prepregs, 462 pressure drop, 223 principal direction, 251, 257 PRO-Prefrom-RTM, 464 Puck criteria, 370–1, 435 quality monitoring, 106 rear pressure bulkhead, 445–6 reinforcement density, 339–41, 343–4 relative bending rigidity, 139 repeating unit cells (RUC), 405 representative volume elements (RVE), 360, 405, 416, 417–18 definition, 363–9 handling non-periodicity, 368–9 NCF geometry example, 364–5 unit cells of ply, laminate, composite and damaged composite, 365–8 meso models biaxial 0/90 and multi-axial NCF composites, 361–2 resin, 337–9 resin film infusion (RFI), 166, 443 resin infusion, 463 resin infusion under flexible tooling (RIFT), 166 resin-rich zones (RRZ), 364–5, 378–9 resin transfer moulding (RTM), 67, 166, 242, 443, 463, 465, 468 Reynolds number, 243, 246–7 rotor blade technology, 482–3 RTM6, 394 RTM-Worx, 242 rule of mixtures (ROM), 407–9 SAERfix EP, 65 SAERfix UP, 65 SAERTEX Wagner GmbH & Co. KG, 64 scissoring, 381

521

semi-laminar analysis non-crimp fabric composites stiffness and strength modelling, 402–36 stiffness models, 405–20 strength models, 420–35 sewing robots, 72 shear lag, 314 shear loading, 418 shear locking, 392 shear strain energy, 150 sheet moulding components (SMC), 462 short beam shear test, 266 simple linear elastic law, 397 single-step preforming, 470–2 skewed fabrics, 485–6 slave surface, 397 SOLID45, 428 spacer warp-knitted non-crimp fabric, 21–2 fabric set-up, 21 illustration, 21 working principle, 21–2 double needle bar raschel machine, 22 spacings, 339 stamping, 452 standard deviation, 218 stiffness evolution, 319–24 stitch density, 346, 354 stitch type, 339–41 stitching, 336 change in the geometry after shearing, 98–100 biaxial non-crimp fabric, 99 configurations, 339–41 distortions, 92–6 carbon non-crimp fibre distortions, face and back, 93 classifications, 92–4 dimensions, 95–6 dimensions definition of an opening, 94 fibre distortions dimensions in different non-crimp fabrics, 96 openings and channels inside a composite plate, 94 width distribution of fibre distortions, 95 effect on mechanical properties and damage of NCF composites, 360–83 damage accumulation, 372–83 elastic analysis, 369–72 internal composite geometry models, 361–2 representative volume element, 363–9 fibres distortions in the plies, 92–8 fibre volume fraction in the plies and deviations of fibre directions, 97–8 gaps between the non-crimp fabric layers in a laminate, 97 fibrous plies general parameters, 85–6 geometry, 86–92 stitching loops actual spacing, 89 stitching sites positions, 89 knitting patterns, 86–9 knitting needles and guides interaction, 87 pattern formation, coding and knitting patterns, 88 stitching loop geometry, 90–2 stitching loops shapes, 91 stitching yarn dimensions, 91


522

Index

understanding and modelling the effect on non-crimp fabrics geometry, 84–101 geometrical model of NCF in WiseTex software, 101 non-crimp fabric geometrical model, 100 stitching–compression (SC), 123 stitching–shear (SS), 123 stitching–tension (ST), 123 Stokes equations, 244–7 strain invariant failure theory (SIFT), 428 stress concentration, 371–2 structural stitching, 187, 336 advantages and challenges, 68 applications and future trends, 81–2 effect on mechanical properties, 343 ellipse formation laminate with half axis, 77 layer set-up influence in the laminate, 77 machine parameters, 78 thread material, 78 factors influencing laminate and part quality, 68 non-crimp fabric preforms for composites, 67–82 quality aspects, 74–81 reduction in ellipse size by preform compaction, 79 seam type related applicability of stitch types and threads, 76 stitch density on compaction pressure, 80 stitching on biaxial NCF flow front, 81 surface characteristic due to fibre concentration and matrix shrinkage, 79 stitch formation lock stitch formation, 71 one-side stitch and micrograph, 73 stitching heads and stitch formation using blind stitch, 73 tufting head and stitch formation diagram, 74 stitching technology and sewing machines, 70–4, 75 2D-sewing plant for manufacturing of plane preforms, 75 flexible robot systems, 75 stitch type and related influence on preform characteristics, 72 threads, 68–70 carbon fibre sewing threads types, 70 classification for yarn types to be used for stitching, 69 structural stitching yarns, 339–41 structurally stitched laminates, 335 structurally stitched NCFcomposites [A1-B-A2]-HTA laminates in-plane tensile modulus, 350 in-plane tensile strength, 352 normalised in-plane tensile modulus and strength, 343 unit cell model, 348 [A1-(B/2)s -A2]2 -HTA laminates in-plane compression modulus, 351 in-plane compressive strength, 353 normalised in-plane compressive modulus and strength, 344 [A1-(B/2)s -A2]2 -HTS laminates in-plane shear modulus, 351 in-plane shear strength, 353

[A1-(B/2)s -A2]-HTS laminates normalised compressive strength after impact, 346 normalised in-plane shear modulus and strength, 345 normalised mode I energy release rate, 347 defect typology and characterisation, 341–7 averaged void cross-section and width, 342 compression strength after impact, 346 in-plane compression stiffness and strength, 344–5 in-plane shear stiffness and strength, 345–6 in-plane tension stiffness and strength, 343–4 laminate thickness and fibre content, 342–3 µ-CT picture and micrograph, 341 mode I energy release rate, 346–7 normalised fibre volume content and thickness, 342 structural stitching on mechanical properties, 343 future trends, 354–5 structural stitching on in-plane and out-of-plane properties, 354 materials and stitching configurations, 337–41 carbon fibre NCF specifications, 338 non-crimp fabrics and resin, 337–9 parameter configurations, 340 stitching patterns, resulting stitch and reinforcement densities, 340 structural stitching yarns and stitch type, 339–41 tension, shear, compression strength after impact, mode I energy release rate and compression tests lay-ups, 339 mechanical behaviour simulation, 348–54 flowchart for determination of elasticity constants, 349 flowchart for strain and stress analysis, fracture analysis and degradation analysis, 349 in-plane elasticity and strength properties, 350–2 in-plane strength components, 352–4 unit cell model, 348–50 mechanical properties, 335–55 future trends, 354–5 NCF laminates characterisation, 341–7 non-structural and structural stitching, 336 structure decomposition, 458 sub-preform, 453 super-elements, 416, 419, 436 Super Light Car, 462 superficial density, 218, 220 tailored reinforcement manufacturing, 450 tailored reinforcements, 451–2 Tape weave, 26–7 fabric set-up, 26 weave made of rovings, 26 working principle, 26–7 illustration, 27 TECABS, 465 technical cost modelling (TCM), 496–504 capital equipment, 503–4 costs for processing large wind turbine blades, 503


Index tooling variable definitions, 504 variable definitions, 503 cost modelling variables, 504, 505 effect of production volume, 499–500 thermoset and thermoplastic manufacturing, 499 global simulation variables affecting all processes, 498 materials, 500–3 cost comparison of non crimp fabric and woven, 500 effect of reinforcement cost on component cost, 502 material costs, 501 material information, 501 non-crimp fabric carbon biaxial cost between 2003 and 2010, 502 part area on, 500–3 part definition, 497–9 part surface area and cost for manufacture of shells of large wind turbine blade, 498 setting global simulation variables, 497, 498 tooling, 504 tensile fatigue, 310 tensile loading, 290–6 tensile test, 265–6 tensile–tensile fatigue tests, 315–16 TexComp, 337 textile reinforcements, 72, 103 textured threads, 69 thermoplastic sewing threads, 68 through-thickness permeability, 223, 230–1 TIGER, 449 tows, 93 transverse failure stress, 429 transverse matrix strength, 436 Tresca criterion, 427, 430 Tsai-Hill failure criterion, 395 Tsai-Wu criterion, 434 twisted multifilament yarns, 69 uniaxial deformation, 376 unidirectional-based composites, 319, 321, 328 unidirectional-based laminates, 310, 311, 321, 323–5 unidirectional prepregs, 489–91 unit cells, 337, 363, 383 model, 348–50 ply, laminate, composite and damaged composite, 365–8 rectangular unit cell of layer and non-matching skewed UC’s, 368 representative capability with the classical periodic boundary conditions, 368 stitch model, 151–3 unstitched laminates, 335 Vacuum-assisted Resin Infusion (VARI), 67 vacuum-assisted resin transfer moulding (VARTM), 166, 242, 443, 486–7, 489, 491 vacuum infusion, 486, 501, 504, 507–8 VESTAS, 482 Vetrotex, 69 viscous constitutive model, 157 visible impact damage (VID), 301, 302 von Mises failure criterion, 434 von Mises theory, 426–7

523

warp-knitting, 5, 86 waviness, 220 weft carriage system, 7–8 illustration, 8 weft technologies, 487–9 whole cracks, 291–4 densities, 293 two 90° fibre bundles, 292 wind turbines blade deflecting under loads, Plate XIV evolution material choice in wind rotor blade technology, 482–3 possible and frequently used warp weight in unidirectional materials, 487 skewing process using Malimo or Liba knitting machine, 485 weft insertion possibilities using NCF production machine, 488 future trends aerodynamic performance optimisation, 492 larger and longer blades manufacture, 492 production consistency, 492 production in segments, Plate XVI materials used in nacelle construction, 491–2 nacelle cover under load, Plate XV non-crimp fabric composites, 481–92 blade length over time, main times of build of different blade lengths, 484 typical blade design, middle section, two shear webs, 484 non-crimp fabric composites development, 483–91 buckling simulation of a blade, 489 central spar design, 490 impact of infusion technology, 483–4 skewed fabrics introduction in late 1980s, 485–6 traditional woven structures in wind rotor blades, 484–5 typical blade layout IEC class II, Plate XIII unidirectional prepregs in wind rotor blade design, 489–91 vacuum-assisted resin transfer and growth of non-crimp fabrics, 486–7 weft technologies development in non-crimp fabric reinforcement structures, 487–9 oil crisis as initiator for wind energy, 481–2 unit material cost per unit of strength for a beam, 483 WiseTex, 243, 256–7, 337 model of biaxial and quadriaxial non-crimp fabric, Plate II woven fabric composites, 311, 317, 331 woven non-crimp fabrics, 23–7 advanced synchron weave, 24 Leno weave, 25–6 Tape weave, 26–7 wrapping technology, 69 X-ray radiography, 283–5 yarn density, 341, 344–6 yarn failure, 347 zone definition model, 394, Plate VIII Zwick machine, 121


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