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Drape and conformability

The terms "drape" and "conformability" are currently used interchangeably within the composites industry, with no clear definition for either term.  The Textile Institute Terms and Definitions [1] offers:

New definitions that might usefully be adopted by the reinforcements industry for drape and conformability respectively have been proposed:

Table 1: proposed definitions for drape and conformability [2]

 

Definitions

Conformability

The ability of a fabric to be shaped to closely follow a contoured surface with the assistance of an operator or of mechanical devices.

Drape

The natural ability of a fabric to conform to a curved surface without assistance.  Suitable test methods may include ASTM D1388, ASTM D4032, ASTM D5732, BS 3356 or BS5058.

Woven fabrics

Woven fabrics normally consist of two sets of interlaced orthogonal fibres produced on a loom.  The warp fibres run along the length of the roll of cloth, while the weft fibres run across the roll.  When the shuttle passes alternately right-to-left then left-to-right, there is continuity between adjacent weft fibres known as a self-finishing edge (selvedge).

fabric warp and weft

When used for the reinforcement of composites, these textile fabrics are normally woven in one of the three styles represented below. [NRLP] indicates Figures drawn by Neil Pearce.

plain weave: twill weave [NRLP]: 5-harness satin weave [NRLP]:

Crimp is defined [1] as "the waviness of a fibre" and is normally expressed numerically as either "the number of waves or crimps per unit length" or "the difference in distance between points on the fibre as it lies in a crimped condition and the same two points when the fibre is straightened under suitable tension". The mechanical properties of composites reinforced with these fabrics increase as the crimp decreases, but drape and in-plane permeability normally decrease as the crimp decreases.  See the Carr Reinforcements website for a comparison of the properties of different weave styles.

To improve the in-plane permeability of twill or satin fabrics, flow-enhancement tows (FET) may be introduced as in, for example, Hexcel Injectex fabrics:

5-harness satin weave with flow enhancement tows, (eg Brochier Injectex) [NRLP] optical micrograph of Injectex fabric reinforced composite digitally enhanced partial cross-section
of the composite micrograph [by Paul Russell - PMS]

The colour-coded image shows the normal horizontal tows normal to the plane of the image (green), one flow-enhancing tow normal to the plane of the image (blue) and transverse tows (red).  Note the lenticular shape of the normal tows, the elliptical shape of the flow-enhancing tow and the large resin rich area adjacent to the flow-enhancing tow.  An alternative approach to flow-enhancement was developed in a collaboration between Carr Reinforcements and the University of Plymouth (EPSRC Grant GR/K04699).  The effect of fibre clustering and the consequent resin-rich regions is discussed under mesomechanics.

A fabric with an equal number of weight of tows in the two orthogonal directions is described as balanced.  For some applications, the majority of fibres may be oriented in one direction (usually the warp for structural reasons) with a small quantity of lighter fibres at 90° (usually the weft) to produce a unidirectional fabric. There is no definitive transition point from an unbalanced fabric to a unidirectional fabric with figures of between 75-90% [3a], 80% or more [3b] or at least 95% [3c] used for the fibre weight in the principal direction. An alternative definition is "A fabric having reinforcing fibres in only one direction" [4].

Whilst the vast majority of woven reinforcements are in the form of two-dimensional planar fabrics with orthogonal fibres, it is also possible to produce triaxial weaves (fibres at 0, ±60°).  There is increasing interest in 3-D textile reinforcements which find application primarily as preforms for Liquid Composite Moulding processes.  Bogdanovich and Mohamed [5] have published a well-illustrated review of three-dimensional reinforcements in which they make a clear distinction between 3D interlock weave (either layer-by-layer or angle-interlock, with binder fibres crossing more than one tow) and 3D orthogonal non-crimp weave (with binder fibres running at 90° to the two other sets of tows).

Layer-to-layer interlock 3D weave   Angle-interlock 3D weave   Orthogonal non-crimp 3D weave
   
Images are reproduced from reference [5] by kind permission of Alexander Bogdanovich at 3TEX Inc.

Braids

Braiding is defined by the Textile Institute [1] as "the process of interlacing three or more threads in such a way that they cross one another and are laid in a diagonal formation", and is the subject of four books [6-9].  Flat tubular or solid constructions may be formed in this way.  A typical braiding machine operates using a "maypole" action whereby half of the yarn carriers rotate on a clockwise path whilst weaving in and out of the remaining 50% of the yarn carriers which are following a counter-clockwise path.  In the tubular braided reinforcement, each fibre follows a helical path around the principal axis of the braid. Ayranci and Carey [10] have reviewed the use of 2-D braided composites for stiffness critical applications, while Li et al [11] considered 3D braiding technology. Hu and Gu [12] considered impact damage to braided composites .

The modelling of the mechanical properties of textile braids has been considered by a number of authors [e.g. 10-17].

Weft-Insertion Warp-Knit or Warp-Insertion Weft-Knit (WIWK)

Bellara [18] states that "yarn in a knitted fabric follows a meandering path forming symmetric loops".  This produces a fabric with more elasticity (more easily stretched) than woven counterparts.  The fabric is considered to consist of courses (the horizontal row of loops) and wales (the vertical lines).  In warp knitting each stitch within a row has a separate thread, while in weft knitting there is one yarn per row.  Warp knitting is harder to unravel, while weft knitting produces more elastic fabrics.

Raz [19] considers warp knitting to be by far the most versatile fabric production system in textiles.  Warp knitted fabrics can be produced flat, tubular or three-dimensional, to be elastic or stable, and with an open or closed structure.  Fabric width can be over 6 m wide without seams (or a multiple of this width if it is a net construction).  Warp knitting machines are divided in two categories: tricot machines and Raschel machines.  Raschel machines are normally used for the production of technical textiles.  Stitch-bonding machines are regarded as a special form of warp knitting machines, especially suited for the manufacture of technical textiles, non-wovens and composites.  The principle of weft insertion in warp knitting involves the insertion of the reinforcement fibres in parallel across the whole width of machine.  According to Raz [19], the advantages of weft insertion systems are:

Stitched fabrics

Stitched fabrics use a lightweight fibre as a loop (left-hand figure below) sewn or knitted around the reinforcement tow to create the fabric (photograph of a real reinforcement at centre figure below).   The fabrics may be just a single layer, or multiple layers.  A multi-layer fabric may be biaxial (0°/90° or ±45° cross-plied for two layers, or 0°/90°/0° for three layer with two parallel layers) or multi-axial (e.g. triaxial as 0°/+45°/-45° or quadriaxial as 0°/+45°/-45°/90°).   The reinforcement tow remains aligned in the plane without crimp (so these reinforcements are commonly referred to as non-crimp fabrics (NCF)).   In consequence, they have the potential for a higher fibre orientation distribution factor than for a woven fabric and each layer can pack as a unidirectional with the possibility of higher fibre volume fractions (see photograph of a cross-section at right-hand figure below).  It is important that full consideration is given to selection of the stitching fibre as poor resin penetration or a poor bond to this thread could be a precursor to laminate failure.

detail of the stitchphoto of real fabric with zigzag stitchescross-section of laminate

Knitted preforms

The concept of knitting net-shape preforms for complex components dates back many years.  Knitting can producereinforcement preforms with negligible waste of the fibre.  Marvin knitted rocket nose cones back in the 1960s [20-22].  The introduction of digital control has caused a step-change in near-net preform production [23].

Preform Technologies, based in Derby, completed a two-year Knowledge Transfer Partnership (KTP) project with the University of Derby in 2017 which modified and adapted a Stoll CMS 822 HP v-bed weft (flat) knitting machine to retain its full functionality while knitting carbon fibre preforms [24].

Embroidery

The Manufacture of Structural Composites using Embroidery Techniques (MASCET) project investigated both Cornely and Schiffli embroidery techniques for enhanced local reinforcement of substrate preforms for liquid moulding processes.  The project developed three technical demonstrators, (i) an automotive spacesaver wheel, demonstrating reduced weight over its steel equivalent; (ii) a generator drive end frame, demonstrating waste and assembly time reduction, plus weight saving over the conventional alloy part; and (iii) a patch reinforcement to strengthen the safety belt anchorage points on a prototype automotive floorpan [25].

Morris et al [26] investigated the effects of embroidery parameters upon processing and mechanical properties of Cornely embroidered quasi-unidirectional reinforcement which improved control of the reinforcement microstructure and achieved marginal improvements in mechanical properties. The technique has only attracted limited further publications [e.g. 27-29].

Adhesively-bonded reinforcements

There are a variety of "reinforcements" in which the fibres are held together by an adhesive or polymer ranging from those held together with a small proportion of binder through semi-preg to fully pre-impregnated (pre-preg) materials.  These include:

References

  1. CA Farnfield and PJ Alvey, Textile Terms and Definitions - seventh edition, The Textile Institute, Manchester, 1975.  ISBN 0-900739-17-7.
  2. J Summerscales and S Grove, Manufacturing Methods for Natural Fibre Composites, Chapter 16 in A Hodzic and R Shanks (editors): Handbook of natural fibre composites: Properties, processes, failure and applications, Woodhead Publishing, Cambridge, 2013, 176-215. ISBN 978-0-85709-524-4 (print). ISBN 978-0-85709-922-8 (online).
  3. (a) Gurit Guide to Composites (undated), and Unidirectional Fabric, http://www.netcomposites.com/education.asp?sequence=40 accessed 15:34 on 01 December 2009.
    (b) Eric Taylor (Carr Reinforcements), E-mail dated Wednesday 02 December 2009 at 08:57.
    (c) Julian Ellis (Ellis Developments), E-mail dated Tuesday 01 December 2009 at 16:01.
  4. Knit-e-pedia Glossary, http://www.knitepedia.co.uk/glossary/u_words.htm accessed 15:39 on 01 December 2009.
  5. AE Bogdanovich and MH Mohamed, Three-dimensional reinforcements for composites, SAMPE Journal, November/December 2009, 45(6), 8-28.
  6. Y Kyosev, Braiding Technology for Textiles: principles, design and processes, Woodhead Publishing, Cambridge, 2014.  ISBN 978-0-85709-135-2.
  7. S Rana and R Fangueiro, Braided Structures and Composites: production, properties, mechanics and technical applications, CRC Press, Boca Raton FL, 2015.  ISBN 978-1-4822-4500-4.
  8. Y Kyosev, Advances in Braiding Technology: specialized techniques and applications, Woodhead, Cambridge, 2016.  ISBN 978-0-08-100926-0.
  9. JP Carey, Handbook of Advances in Braided Composite Materials: theory, production, testing and applications, Woodhead, Cambridge, 2017.  ISBN 978-0-08-100369-5.
  10. C Ayranci and J Carey, 2-D braided composites: a review for stiffness critical applications, Composite Structures, September 2008, 85(1), 43-58.
  11. X Li, X He, J Liang, Y Song, L Zhang, B Wang, J Ma and G Kong, Research status of 3D braiding technology, Applied Composite Materials, 2022, 29, 147-157.
  12. M Hu and B Gu, Impact Damages of Braided Composites, Springer, Singapore, 2022. ISBN 978-981-16-5702-3.
  13. BN Cox, WC Carter and NA Fleck, A binary model of textile composites I: formulation, Acta Metallurgica et Materialia, 1994, 42(10), 3463-3479.
  14. J Xu, BN Cox, MA McGlockton and WC Carter, A binary model of textile composites II: the elastic regime, Acta Metallurgica et Materialia, 1995, 43(9), 3511-3524.
  15. MA McGlockton, BN Cox and RM McMeeking, A binary model of textile composites III: high failure strain and work of fracture in 3D weaves, Journal of the Mechanics and Physics of Solids, 2003, 51(8), 1573-1600.
  16. RA Naik, Failure analysis of woven and braided fabric reinforced composites, Journal of Composite Materials, 1995, 29(17), 2334-2363.
  17. Y Qingda and B Cox, Spatially averaged local strains in textile composites via the binary model formulation, Journal of Engineering Materials and Technology, 2003, 125(4), 418-425.
  18. S Bellara, Focus on: knitting, MADE (the magazine for the Design Exchange), 2009, (3), 52-53.
  19. S Raz, The Karl Mayer Guide to Technical Textiles, Report WE 208/1/4/2000, Karl Mayer Textilmaschinenfabrik GmbH , Obertshausen, 2000.
  20. AW Marvin, Some mechanical properties of knitted glass laminates, Journal of the Textile Institute, 1961, 52(1), T21-T25.
  21. AW Marvin, Knitted glass laminates, their production and properties, Hosiery Trade Journal, August 1966, 8(73), 100-102.
  22. AW Marvin, The development of knitted glass fabrics for use in resin lamination, MSc dissertation, University of Strathclyde, April 1969.
  23. G Gardiner, 3D knitting solves preforming cost, time, performance equation, CompositesWorld, 2016, 2(12), 32-37.
  24. Billy Hunter, UK company develops new 3D knitted carbon fibre preforms, Inside Composites, 30 June 2017.
  25. JG Ellis, Embroidery for Engineering and Surgery, Textile Institute World Conference, Manchester, circa 2000.
  26. DJ Morris, CD Rudd, SP Gardner and NA Warrior, The effects of embroidery parameters upon processing and mechanical properties of Cornely embroidered quasi-unidirectional reinforcement, 4th International Conference on Flow Processes in Composite Materials (FPCM-4), Aberystwyth UK, 9-11 September 1996.
  27. NA Warrior, CD Rudd and SP Gardner, Experimental studies of embroidery for the local reinforcement of composites structures: 1. Stress concentrations, Composites Science and Technology, November 1999, 59(14), 2125-2137.
  28. N Torii, K Oka and T Ikeda, Creation of smart composites using an embroidery machine, SPIE Proceedings of Behavior and Mechanics of Multifunctional Materials and Composites, 2016, 98001C.
  29. A Poniecka, M Barburski and M Urbaniak, Mechanical properties of composites reinforced with technical embroidery made of flax fibers, Autex Research Journal, published online ahead of print, 18 June 2021.

Further Reading

  1. MH Aliabadi (editor), Woven Composites (Computational and Experimental Methods in Structures: Volume 6), World Scientific, Singapore, 2015. ISBN: 978-1-78326-617-3.
  2. A Bogdanovich and CM Pastore, Mechanics of textile and laminated composites with applications to structural analysis, Chapman and Hall, London, 1996. ISBN 0-412-61150-3. Now published by Springer as ISBN-13: 978-0-412-61150-6.  PU CSH Library.
  3. M Grayson, Encyclopedia of textiles, fibers, and nonwoven fabrics, Wiley, New York & Chichester, c1984. ISBN 0-471-81461-x.  PU CSH Library.
  4. KL Hatch, Textile science, West Publishing, 1993. ISBN 0-314-90471-9.  PU CSH Library.
  5. JWS Hearle and WE Morton, Physical properties of textile fibres - fourth edition, Woodhead, Cambridge, 2008. ISBN-13: 978-1-84569-220-9.  PU CSH Library.
  6. AR Horrocks and SC Anand, Handbook of technical textiles, Woodhead, Cambridge, 2000. ISBN 1-85573-385-4.  PU CSH Library.
  7. J Hu, 3-D fibrous assemblies: properties, applications and modelling of three-dimensional textile structures (Woodhead Textiles Series #74), Woodhead, Cambridge, 2008. ISBN-13: 978-1-84569-377-0.
  8. FK Ko and T-W Chou, Textile structural composites, Elsevier, Amsterdam & Ney York, 1989. ISBN: 0-444-42992-1. ISBN-13: 978-0-444-42992-6.
  9. AC Long, Design and manufacture of textile composites, Woodhead, Cambridge, 2005. ISBN 1-85573-744-2.  PU CSHLibrary
  10. A Miravete, 3-D textile reinforcements for composite materials, Woodhead, Cambridge, 1999. ISBN 1-85573-376-5.
  11. P Schwartz, Structure and mechanics of textile fibre assemblies (Woodhead Textiles Series #80), Woodhead Publishing, Cambridge, 2008. ISBN-13: 978-1-84569-135-6.
  12. X Tao, Smart fibres, fabrics and clothing, Woodhead, Cambridge, 2001. ISBN 1-85573-546-6.  PU CSH Library.
  13. SW Yurgatis and J Jortner, Characterisation of yarn shape in woven composites, Chapter 5 in J Summerscales (editor):
    Microstructural Characterisation of Fibre-Reinforced Composites, Woodhead, Cambridge, July 1998, pages 159-178.  ISBN 1-85573-240-8.  PU CSH Library.
  14. JJ Crookston, AC Long and IA Jones, A summary review of mechanical property prediction methods for textile reinforced polymer composites, Proc IMechE Part L - Journal of Materials: Design and Applications, 2005, 219(2), 91-109.
  15. Zheng Ming Huang and S Ramakrishna - Micromechanical modeling approaches for the stiffness and strength of knitted fabric composites: a review and comparative study, Composites Part A: Applied Science and Manufacturing, 2000, A31(5), 479-501.
  16. KH Leong, S Ramakrishna, ZM Huang and GA Bibo, The potential of knitting for engineering composites, Composites Part A: Applied Science and Manufacturing, 2000, A31(3), 197-220.
  17. R Kamiya, BA Cheeseman, P Popper and T-W Chou - Some recent advances in the fabrication and design of three-dimensional textile preforms: a review, Composites Science and Technology, 2000, 60(1), 33-47.
  18. AP Mouritz, MK Bannister, PJ Falzon and KH Leong - Review of applications for advanced three-dimensional fibre textile composites, Composites Part A: Applied Science and Manufacturing, 1999, A30(12), 1445-1461.
  19. AP Mouritz, KH Leong and I Herszberg - A review of the effect of stitching on the in-plane mechanical properties of fibre-reinforced polymer composites, Composites Part A: Applied Science and Manufacturing, 1997, 28(12), 979-991.
  20. P Tan, L Tong and GP Steven - Modelling for predicting the mechanical properties of textile composites - a review, Composites Part A: Applied Science and Manufacturing, 1997, A28(11), 903-922.
  21. J Summerscales, High-performance reinforcement fabrics, Progress in Rubber and Plastics Technology, 1987, 3(3), 20-32.

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Updated by John Summerscales on 16-Jun-2022 16:16. Terms and conditions. Errors and omissions. Corrections.