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`. Woedheadfublishing in'Textiles: Number 74 .
`
`BED tibreue .
`
`aeeemblies ’
`Properties, applications
`and modelling of,
`three=dimen$ional
`textile structures
`
`'
`
`'
`
`'
`
`.Jlinllian HlU
`
`
`
`CRC Press
`Boca Raton Boston New Yorlk Washington,DC
`
`WOODHEAD PUBLISHING LIMITED
`
`Cambridge England .
`
`000002
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`

`

`Published by Woodhead Publishing Limited in association with The Textile Institute
`Woodhead Publishing Limited, Abington Hall, Granta Park,
`Great Abington, Cambridge CB21 6AH, England
`www.woodheadpublishing.com
`
`Published in North America by 'CRC Press LLC, 6000 Broken Sound Parkway, NW,
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`'
`.
`
`First published 2008, Woodhead Publishing Limited and CRC Press LLC
`© Woodhead Publishing Limited, 2008
`The author has asserted her 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 author and the publishers cannot assume responsibility for the validity of all
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`A catalogue record for this book is available from the British Library.
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`Woodhead Publishing ISBN 978-1-84569—377—0 (book)
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`The publishers’ policy is to use permanent paper from mills that operate a
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`Typeset by SNP Best—set Typesetter Ltd., Hong Kong
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`
`
`Introduction to three-dimensional
`fibrousassemblies
`
`M A
`
`bstractzr'Ihree-dimensional (3-D) textiles are those materials that have
`, a system or systems in all three axes of plane. These materials offer
`particular properties, such as interlaminar shearing force, mechanical and
`thermal stability along all three axes of space, that are not achievable
`with other reinforcements. The development of three-dimensional
`textiles has taken place rapidly over the past two decades. It can be"
`credited largely to the growth of another technology: composite
`materials, which combine fibres and a matrix. An understanding of the
`production methods and structures of these 3-D fibrous assemblies
`'
`would go a long way in design, process control, process optimization,
`, quality control, clothing manufacture and development of new
`techniques for specific end uses. This chapter introduces various 3-D
`woven, knitted, non-woven, braided and stitched fabrics with their brief
`description and advantages.
`
`Key words: three—dimensional (3-D) textiles, 3-D woven fabrics, 3-D
`knitted fabrics, 3-D non-woven fabrics, 3—D braided fabrics.
`
`1.1‘
`
`Introduction: concepts of three-dimensional
`fibrous assemblies
`
`Textile structures such as in woven, knitted, non—woven and braided fabrics
`are being widely used in advanced structures in the aerospace, automobile, _
`geotechnical and marine industries. In addition, they are finding wide appli-
`cation as mediCal implants such as scaffolds, artificial arteries, nerve con—
`duits,heart valves,bones,sutures, etc.This isbecause theypossess outstanding
`physical, thermal and favourable mechanical properties, particularly light
`weight, high stiffness and strength, good fatigue resistance, excellent corro-
`sion resistance and dimensional stability. In addition, they act as attractive
`reinforcing materials in various composite applications with low fabrication
`cost and easy handling (Tan et al., 1997). With high-end applications such
`as in aerospace, the orientation of- the fibrous reinforcement is becoming
`more and more important from a load-bearing point of View, as is the need
`for placing the reinforcement oriented in the third dimension (Alagirusamy
`et al., 2006).
`-
`'
`'betile fabrics, termed preforms in composites and other applications,
`consist of various reinforcing fabrics such as wovens, knits, braids and
`
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`_ non-Wovens. Two-dimensionalfabriCs have allowed us to drape bed,board
`_ and body"m a profusion of texture, pattern and colomI over thecenturies
`- The development. of advanced fibres has led engineers to consider textiles
`for hlgh—performance applications such as in construction and aeronautics
`These fabrics have been relatively well deVel'oped111 terms of production,
`analysis and application andsome of them have longbeen used'1n structural
`composite fields (Chou and Ko, 1989; Mohamed 1990); However, the
`, strengthof these traditional fabrics'is anisotropic, manifesting itself primari
`: ily'1n the diract-ion of the fibreorientations. Mostof these 2-D textile struc-
`.tures retain ”the inherent weakness of. laminated composites that are
`.
`susceptible toIdelarnination.-
`--
`-
`-
`To extend the use and value of textiles into industrial and engineering .
`applications, which typically require strength'1n more than two directions, I
`.'- textile designers have bound together.layers of textiles and exploited the.
`- chemical properties of fibres and binders to createI'IovIel non—woven textiles .
`‘ whose fibres are not restriotied to twoedirnensional‘arrangements More.
`-
`recently, they have taken. the next step: finding ways to manufacture true I
`"-.
`three-diniensional (3-D) textiles. Hence, 3-D fabrics have been introduced .
`-to respond to the needs of a number of industrial requirements such asI- I-
`composites capable of withstanding multidirectionalstresses.
`The development of3-D textiles has taken place rapidly over the past.
`We decades. It can becredited largelyto thegrowth of another technology: I '
`. composite- materials, which combine fibres and a-matrix. Textile engineers
`~
`have beenchallenged to develop strong fibre architectures and new manug,
`facturing-processes for building. textile structures in three dimensions, as :..
`. these 3-D fabrics hold great promise for use in industry, construction, trans- .
`portationIand even military andspace applications They are often made :-
`into a near net shape so that the overallmanufacturing cost can be very .'
`low for certain applications (Mohamed, 1990).,
`An understanding oftheproductionmethodsandstructures of these3-sz
`fibrous assemblies would go a long way in the design, process control, .'
`IIprocess optimization, quality. control, clothing fabrication and the develop; '
`merit of new techniques for specific end uses. Theinterrelationship between.
`- theirstructure and various properties may be of great help'1n designingnew
`types of 3—D structures for the construction, medical, sportsand aerospace '-
`industries.
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`- 1.2. Two-dlmensmnal structures I
`(two-dimensmnalII-fIabrics)
`1.2.1 Two~d1men310nalwoveIns
`Weaving-is the most widely used textile manufacturing technique and
`acCounts for the majorityIIof the two-dimensional (2-D) fabricproduced'1
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`(Stobbe and Mohamed-,-2003); Woven structmes have the greatest history '
`ofapplication'1n textilemanufacturing. Conventionalwoven fabrics coInSist ‘.
`.'::,'of tWo sets of yarns mutually i11te1la<1ed into a textile fabric.structure. The
`-.threads that run' along-the length of the fabric are called Warp or ends, While
`the threads that run along theWidth .of _the fabricfrom selv'e'dge.to .selvedge
`are referred to as Weft or picks. Warp .I'andWeft yarnsare; mutually posi-
`Etioned at an angle of 90°. The number ofwarp andWeftyarns per unit length 1
`is called the warp and weft density The Warpand Weft yarnsin a woven I-
`~ fabric can beinterlaced'111 various Ways, called-a_ Weave structure. The struc-
`V't-urIeII'in which Warp yarns alternately lift and go over across one Weftyarn
`‘ and vice .versa is the simplest woven structure, called plain weave (Fig.
`'0 1I.1I(a)). Other common structures aretwill and satin Weave. Twill1sa weave
`that produces diagonal lineson the face of a fabric (Fig. 1.105)). The difec- --
`tion of the diagonal lines viewed along the warp direction can be' from
`' upwards to theIIright or" to the left,makingZ or S twill 1espectively. Compared
`.5:
`_' toplain Weaveof thesame cloth parameters, twills have longer floats, fewer '
`:~.i11te1_sectionsI and a more open const'ructidn Aweave in Which the binding
`.‘ places are arrangedto produce a smooth fabric Surface free from twill lines
`.I'Iis calledsatin (Fig. 1.1-(c)). The distribution of interlacing points must be _as
`'75- random aspossible to avoid ItWillIIlines; The smallest repeatof satin weave
`,. . is 5, While theImostpopularweaves aresatins of 5 and 8 lepeats. The 5-ends
`3."."satIin is1'11Iost frequently used for technical applications for providing _fiIrm
`2‘ I"_-fabr10, althoughhavingamoderate cover factor.
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`.Z'ili‘iaxiaIl-IwoyIéIIIfabrics-
`IAtriaxia‘lI Woven structure consists of.three systems 'of threads: one system
`fer weftandtwo systems for warp. This fabric has three layers of material
`if at any point, andis thus stronger .than arectangularwoven fabric made
`
`;.{4'I1_1'Ising-Ithe same elements.' Warp thread's'in 'a basic triax‘ial fabric are inter-
`
`IIlaced at60° and the structure is fairly open with a diamond-shapedcentre
`i;(EigtI1.2(a)).--A modification of basic triaidal fabric1s'basket- weave, which I,
`i.‘
`formsa closerstructure With different characteristics (Fig1.2(b)).
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`.1-1."2Triaxial fabrics.
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`-Triaxial fabrics possess exceptional mechanical properties inseveral
`. directions:Since the interlacing points are fixe‘d into the fabric Structure,
`-
`these fabricsexhibithighshear resistance (Lee 'et .aL-,.2002).
`1.22 TWo-dimensional. knits
`Knitted fabricsare textile structures assembled fron1 basic construction ,
`units called loops.-There exist two“ basic technologies formanufacturing
`knitted structures: weft and warp-knitted technology
`-
`
`Weft-knittedfabric _'
`'
`The repeatingunit of the knitted fabriciscalled the loop. The feature of" , 1‘
`-;weft-kn1tted fabricis that the loops of one row of fabric are formed from
`the same yarn. A horizontal row of loops in a knitted fabric is Called a-.
`coarse, and a_vertical 10111 of loopsis called a wale. In Weft-knitted fabrics
`the- icopsare forrned successiveiy along the fabric width. The feature of
`weft-knittedfabricis.that the neighbouring loopsofone course.arecreated
`_ of thesame yarn. .The simplest weft knit strueture produced by the needles '. .1
`.of one needle-bedmachine'1s called plain knit. or jerseyknit (Fig. 1.3(a).) _.
`'.
`Plain knithas a different appearance on each side of the fabric. A str‘hcture ,
`.
`producedby theneedlesof both needle beds is called a rib structure or
`doiibleJersey (Fig. 1.3(b)) and has the same appearance.on both sides 'of'.‘
`the fabric.‘
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`Warp-knitted.fabfic'1'
`Inwarp-knitted technology every loop inthe fabric structure.is formed ‘_
`from a separate yarn called the. warp, introduced. mainly'1n the longitudinal
`fabric dii‘eCtion The. most characteristic feature. of warp-knitted fabric
`(Fig.1..3(c))-'1s that neighbouringloopsofone course.916 not created frenr
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`. Introduction to three—dimensional fibrous assemblies
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`(c) Basic warp-knit structure
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`(d)'Weft-lnserted warp-knit
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`weft-inserted warp¥knit
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`1.3 Schematic representations of weft- and warp-knitted structures.
`
`, the same yarn. While weft—knitted technology is most commonly used in
`clothing manufacture, warp-knitted technology is substantially engaged in -
`manufacturing structures for technical applications. Of special interest for
`technical applications are structures with inserted weft yarns, called weft-
`inserted warp-knitted fabric. (Fig. 1.3(d)), and a multibar weft—knitted fabric
`(Fig. 13(6)).
`
`1.2.3 Two—dimensional. non—.wovens
`
`Non—woven fabrics are broadly defined as a sheet or web structure bonded
`together by entangling fibre or filaments either mechanically, thermally or-
`chemically."Ihey form a sheet, web or batt of directionally or randomly
`oriented fibres, bonded by friction and/or cohesion and/or adhesion, exclud-
`ing paper and products, that is woven, knitted, tufted, stitch—bonded (incor-
`porating bonding yarns or filaments) or felted by wet milling, whether or
`not additionally needlecl. The fibres'may be of. natural or artificial origin.
`They may form staple or continuous filaments. They are engineered to
`_ provide specific properties such as absorbency, liquid repellency, resilience,
`stretch, softness, strength, flame retardancy, washability, cushioning, filter-
`ing, bacterial barrier and sterility. Abasic non-woven structure is shown in -
`Fig. 1.4. .
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`6
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`3—D fibrous assemblies V
`
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`1.4 Basic non-woven fabric.
`
`1.2.4 Two-dimensional braids
`
`A braid is a textile structure formed by interlacing two or more sets of yarns
`resulting from the carriers rotating in clockwise and counter-clockwise
`- directions (Brunnschweiler, 1953). Braiding has been conventionally used
`for applications such as Shoelaces, ropes, etc. However, in recent years, fibre-
`reinforced composites and medical implants have become interesting appli-
`cations for braiding. This has been achieved by employing 3—D preforms for
`such applications (Zhang et (11., 1997).
`Braided textile structures are manufactured by intertwining or orthogo-
`nally interlacing two (or more) sets of yarns to form an integral structure
`in a tubular form. One set of yarns is- called the axial yarns while the other '
`is called the braided yarns. Hence, the structures of braided fabrics consist
`of parallel axial yarns, interconnected with braided yarns that are placed
`along complex spatial orientations. There are three typical braid structures:
`diamond, regular and hercules. A regular diamond structure is shown
`in Fig. 1.5(a). It is obtained when the yarns cross alternately over .and
`under the yarns rimning in the opposite direction. The repeat notation is
`1/1. Using this notation, the regular braid structure has notation 2/2 and
`hercules 3/3.
`‘
`'
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`Braids are mostly produced in a regular structure, generally in a tubular
`form of biaxial yarn direction. By inserting longitudinally oriented yarns
`(middle-end-fibre) into the structure, triaxial braid is obtained (Fig. 1.5(b)).
`Moreover, in'the Centre of the tubular braid, additional fibres called axial
`fibres can be inserted. When the number of braiding fibre bundles is the
`same, the tubular braid increases the fibre volume fraction more than the
`flat braid (Fig:1.5(c)).-The main feature of the braid is the angle of inter-
`twining, which can vary between 10° and 80° and depends on the yarn
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`Introduction to three-dimensional fibrous assemblies
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`fineness,thetype ofstructure (biaXIiIal or tnax1al), thecoverfactor (tightness '
`-'Iof the structure)andthevolumeIrat-Iio ofthelong1tud1na1yarns:
`,1.3 leltatlons of two-dimensmnal textllestructures_
`3'Polymer laminates reinforced with a 2-D layer fibresItrIucture have been ,
`_' 'used with outstanding silccess.fer over 50 years in maritime craft, for about
`I {30years in aircraft and fornearly,20years inhighrperformance automobiles
`. and civil infrastructure such as buildings and bridges. Despitethe use of 2-D '
`" laminates over along period, their use in many structural applications has
`- beenlimited by manufacturing problems and some inferior mechanical
`properties. The manufacture of laminates can be expensive because, of the
`high,labour requirement inthe manual lay—up of piles (MouriIItIz et alt,
`1'999)-
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`,'Ih'e application of 2-D laminates in some,Critical structuies in aircraft
`‘. and automobileshas also beenrestricted by their inferior impact- damage
`resistance and low through-thickness mechanicalproper-ties when, com- '
`I"I' paredto traditional aerospace and automotivematerials such asaluminium
`”alloys and steelThe low through-thiclmess properties, such as stiffness and -
`".' 'fatigue resistance, have impededtheuse of 2-D laminates111 thick structures
`subjected tohigh through-thickness and interlaininar shearstresses; An -
`.addltional problem is thatmany 2—D laminates.have low resistance, to
`1",,1-'
`delamlnatmn crackingunder impact loading because of their poor inter-
`v,“
`'laminarfracture toughness. Asa consequence of this, their pest-impactin-
`plane mechanical properties can be severelydegraded, particularly. their
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`compressmn strength and fatigue performance. While thesoproperties can
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`1I.4_Three-d1mensmnal structures
`(three-dimensmnal _.fabIIriceI)
`1 .4.iDefInItIon o'iIthree—dlmensmnal fibrous assemblies.
`'I‘hrIee-d1mens10nalwoven,braided or stitched fibrous assembliesare textile"
`architectures having fibres oriented so that both the in-plane and transverse .
`yarnsare interlocked to form anintegrated structure that has a unit cell
`with comparable dintensions'111 all three orthogonal diredtions,1.e., the SD
`" structurebasically consists of in-plane yarns for stiffness andstrength- and
`zrbinder yarns for through-thickness reinfOICement (Yang et 11]., 2004)..In '
`. other words, 3-D textiles are those materials that have a system or systems '
`in allthree orthogonal planes
`-
`-
`-
`These materials offer particular properties, such as interlaminar shear.
`' force, mechanical and thermal stability along all three spatial axes,- that are I'-
`not achievable with other reinforcements. 'IIlIns integrated architecture 1110-.
`vides improved stiffness.and strength in the transverse direction and'I
`impedes the separation of in—plane layers"1n Comparison .to traditional 2-D " .
`fabrics. Because of their high transverse strength, high-shear stiffness,.low '
`delaminafiontendency and- near—net-shape manufacture, textile composites
`'II from weaving,knitting and braidinghave received tremendous attention-
`' recently (Xuekum Sun and.Changjie Sun, 2004). Recent automated manu~-
`'IfaCturIing techniques have substantially reduced costs and significantly:
`"
`improved the potential for- large-scalepreductionh
`'1
`Optimalorientations fibre combinations and distributions of yarns have -
`‘ert to be fully developed and perfected for 3—D fabrics Subjectedto, I'
`impactloading conditions. For example, current body armour relies on '
`'ceramic plates to defeat penetrators. The rigidity and-brittleness: of these .
`'
`materials limit their use to military fighting applications In addition, overI-
`time,environmental degradation and accidental mechanical impact damage
`-
`the ceramic and render it ineffective. Hence, there are ample opportunirI,
`'ties' for substitute materials, and innovative concepts that combine. hybrid '-
`3-D fabrics with othermaterialssuch as ceramic. and possibly new‘ 1.131197.
`'
`scale materials are needed. The optimal combinations of these materials
`need to be determined alongwith new methodologies to ascertain ho'v'v-‘. '
`to utilize the inherent mechanisms (fiic'tion,_1nicro-c_racking,Ifib‘re break-.
`I-a‘ge, ”fibre bridging,I etc.)-ofI: these systems for energy dissipationand.
`-strengthenmg
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`'. Iinterleaves, .these solutions. are usnally expensive anddo not: overcome
`many.oftheproblemsassociatedwiththemanuiacture.ofI-lanfinates I(MquritIz -
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`Introduction to three—dimensional fibrous assemblies
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`3-D solid
`— multilayer
`-— orthogonal
`— angle interlock
`3-D hollow
`—- flat surface
`— uneven surface
`3-D shell
`
`— by weaVe combination
`— by differential take-up
`— by moulding
`a ,3-D nodal.
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`Three-dimensional woven solid fabrics produced by the multilayer prin-
`ciple are characterized by the presence of several layers of yarns woven '
`together by using different interlacing techniques. .The layers can also be
`stitched together and the stitching arrangement may have either a self-
`stitching or a central stitching arrangement, Wadding yarns may also be
`incorporated into the structure for specific applications. It is important to
`control the yarn ratio in the fabric to obtain specific properties (Xiaogang
`Chen, 2006).
`Three-dimensional solid orthogonal fabrics feature straight warp, weft
`' and vertical yarns in their design. The number of layers of straight weft yarn
`is always one more than that of warp yarn, and the amount-of vertical'yarn
`depends on the binding weave. Two options are possible: ordinary and
`enhanced. It is possible to have a variable interlinking depth.
`The 3-D solid angle interlock principle involves the binding of straight
`walp. yarns by interlocking warp yarns. Warp yarns can be bound to differ-
`ent depth. As in orthogonal fabrics, wadding’yarns may be used in the
`structure. The structures of various 3—D solid woven fabrics are presented
`in Fig. 1.7 (Xiaogang Chen, 2006).
`'
`.
`Three-dimensional hollow structures are of'two types: one with a flat
`surface, and the other with an uneven surface. The hollow structures with a
`flat surface are based on the multilayer principle but with different fabric
`section lengths. Such structures should be self-opening under the right
`conditions. It is possible to have multilevel cells in their structure. The
`hollow fabrics with uneVen surface structures are based on the multilayer
`principle and are created by joining and separating adjacent layers. Such
`structures need opening. The cells created in the structure are generally of
`hexagonal shape. Different 3-D hollow structures are shovtm in Fig. 1.8
`(XiaogangChen, 2006).
`,
`.
`-
`Three-dimensional shell structures can be created either by using differ- .
`ent weave patterns 'or by employing a discrete take-up in the loom to
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`.- 12
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`3-D fibrous} assemblies
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`' 6'-layer Weave
`' " . Enhanced angl‘eI ‘-
`6-layer Wiih wIaddihg-I
`I "
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`interlockWeave
`.
`(d)_ 3-D angle interlock weave
`. 17 3-_D solid woven structures(adapted fromIXiaogang IChen, 2006).
`
`_
`
`I modify their.structure to have a hollow-type surface. Sometimes it is possi-_
`bleto mould these fabrics to obtaina special moulded structure fortechni-'
`eal or industrialapplications. Three different types ofhollowstructuresare
`shown”m Fig. 1.9.
`Three-dimensional nodal fabrics (Fig. 1.10) refer to joining tubes to
`'I obtaincertain special types of structures for industrial applications. The
`‘._w'a1ls-of the tubes- may be 3-D solid structures themselves. All tubes 'must
`be'in the same plane (x~y_)The design procedure involves creating a nodal
`design111 2-D space,flattening, area segmentation and assignment ofIweaves
`for.different sections (Xiaogang Chen,2006).
`.
`A 3-D weave containsmultiple planes of nominally- straight warp and '
`Weft yarns that areconnected together by warpWeavers to form an integral -
`structure.The most-common classes areshown'in Fig. 1.11.Within each class, I
`there areI‘sIevera'l parametersthat can be varied." '
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`Introduction to three-dimensional fibrous assemblies
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`13
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`(c) 3-D hollow uneven surface
`
`1.8 3- D woven hollow structures (adapted from Xiaogang Chen, 2006).
`
`The angle interlock type of structure is a variation of 2-D weaving wherein
`more than two yarns are in the thickness direction. The angle interlock
`struCture allows the preform to be up to 10 cm in thickness. In this fabric,
`warp yarns are used to bind several layers of weft yarns together. Weft yarns
`could be used for binding as well. In place of warp or weft yarns, an addi—
`tional third yarn may also be used as binder. Stuffer yarns, which are straight, _
`can be used to increase fibre volume fraction and in-plane strength.
`'Angle interlock weaves can be categorized by the number of layers that
`the warp weavers penetrate. Figure 1.11(a) shows a through--thickness inter-
`lock fabric, in which the warp weave1s pass though the entire thickness.
`Figure 111(0) and (d) show layer—to—layer interlock patterns, where a given
`weaver connects only two planes of weft yarns but the weavers collectively
`bind the entire thickness. Various intermediate combinations can be fabri-
`cated, with the weavers penetrating a specified number of layers, with the
`warp weavers passing through the thickness orthogonal to both iii-plane-
`'directions, as shownIn Fig. 1.11(b). Interlock weaves are sometimes manu-
`factured without straight warp yarns (stuffers) to produce a composite
`reinforced predominantly in one direction. They may also be fabricated
`with .weft rather than warp yarns used for interlock. A major limitation of
`‘3-D weaves is the difficulty of introducing bias-direction yarns to achieve
`in-plane isotropy. One solution is to stitch additional 2—D fabric plies
`oriented at 45° onto the woven preform.
`
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`14:
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`37D fibrous ass'em'blies
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`('ié.)3-D.shell't'>y~
`'1
`using diffeteht'weaves
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`(13) 3-D shell by
`_dis‘oretg take-up
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`'1.1o 3-D quen hodal st'mctur'ééxadgpted'trém Xiaogang Chg), zoos); .
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`(5) 3—D shefi by _
`mou!ding
`1.9, 3-1:) wéven shell Istructulreé.
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`introduction to three—Idimensionaifibrous assemblies
`.I-,I.
`I. . Filler(IIvefl)I
`I—I‘Stuffe‘r (straight warm-I
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`' 11 2A1 7A1 an 1;! m rAx int 3;! 1;:I 21'
`- I’LC ,AI 74." ’1‘ 7A‘( ,A‘ 'A‘ I’A‘I’LK l'I‘ D"
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`II- I'
`(a)IThrough-IthlcaneIssIangleinterlockI
`SI-Iun‘aIcIe waIrpIIweaver
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`Body warp'
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`' weaver
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`'-I-I (b) OrthogonalInterlock
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`'(c) Layer-tolayerangle Interlock- k,
`s‘Itraight-ihterIiacinIgI structure
`-
`1.11 3-D weave‘I patterns.
`
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`.(d)-Laye_r-to-layerarigieinterlock'
`I. wavy-interlacing structure
`
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`Textile. technology has been invplved'111- theconstruction of3—D shells, '
`I ‘-.'b.1iIt. theseare rather flexible structures for clothing and. similar purposes.
`- For production of strong 3-DIfabrics, cutting,-sewing and jointsshould be.
`avoided as much as-possible.- -TIrue 3—D weaving can be accomplished on
`2 special machines as already developed,The simplest caseofsucha struc—I
`'ature; in which the warp is crossed by twosets of IwIefIts, is shownIn Fig.
`:~
`‘I‘ 1.1I2(a). A Woven structure in Which the multilayer warp moves between
`‘
`the top and bottom ofthe material,thusproviding x andy directions Iat an I.
`,--:angle_ of 45°,and with weft yarns crossingbetween the warpprovrdingthe
`zdirection, is shownIn Fig.1;.12(b).
`'
`.
`_
`In general, a variety.of3-D structu1es can be accomplished.For example,
`-
`thewarp yarns can go only part-way ”aci'oss the whole material (Fig. 1.13(-aI)),
`-or-I one set of warp yarns can be introduced'1'11 the axial direction and one -
`" set:angled, thus providing yarns. in four different directions (Fig 1.”1305)).
`:
`1 “'Ihe latter. structure gives higher-c-ontrol- of the directional properties. of
`the-material. Shaping of 3-D weaves can be accomplished by, varyingthe ,.
`width“. of the warp layers, thus creatingthe required cross-section, for '.
`'-exampleIn the formofa T—beamI(Fig.1.13(c)I)I(Den1osh-iand.Bogoeva-
`GacevaIIZQOIS).
`
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`J-3-D.fibrouéassemblies '
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`:(a)mululayer-slom'avewim f
`"warp-sinxaridyd'irections-
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`(h) Weft in -z dirooiion
`.
`' 71:12 Two types of ni'ultilayerISJD-wovén fabric} (a) Warp in,thé ‘z
`directibn and weftsjnsertedjn the X and_y directions, (b) warps at 45" H
`-‘ In the )g and y directions and Weffjn the z direction:
`‘
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`(b)Tw.o 'sets ofwarp yarns ,
`(é)Eafiial'
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`Interlocking oleayeys
`1_. 13 Variants of 3-D moltilayer'WeévingJ
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`(c)§haping_of.3-theavi‘hg‘byl'j'.'
`vérylng warp Iayors
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`Advantages of thfee-dihjensional ‘woyeh's'tijucmresl
`I, 0
`3-D weaving can'firoduce cOmploi near~oef shaped préfofms.
`c. 3-D woven compositos with a complex‘geomotlr-yoan be Less oxponsivg ‘-
`.-to.produce.~.'
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`c " 3-D weaving allows the tailo‘rixig of proper-ties _fo1f specific applioagio'ns
`0 3-D woven composites Show betto'r- delamhlation resistance and.damagq
`toleraxices:
`-'
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`Introduction to three-dimensional fibrous assemblies
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`17
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`0
`.°
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`3-D woven composites show higher tensile strain~to-failure values.
`3—D woven composites exhibit higher interlaminar fracture toughness
`properties.
`
`1.4.4 Three—dimensional knitted fabrics: .
`In the search for methods to reduce composite manufacturing costs, textile
`preforms, including knitted structures, are receiving increasing interest in
`the composites industry. While conformability and productivity are obvious
`attributes for knitted preforms, the availability of a broad range of micro-
`and macrostructural geometries has only recently been recognized. The
`non-linearity of knitting loops, severe bending of yarns during the knitting
`process and limited fibre packing density, resulting in the formation of resin”
`pockets within a knitting loop, prevent knits from being considered for
`structural applications
`Knitting13 the interlocking of one or more yarns through a series of loops
`- (also called stitches).- Knitted fabrics are considered 3-D due to their non-
`- planar configuration of the loops in the structure; They are also known as
`multiaxial—multilayer structures and are fabrics bonded by a loop system,
`consisting of one or several yarn layers stretched in parallel. Multilayers of
`linear yarns are assembled in warp (0°), weft (90°) and bias (i6) directions
`to provide structural integrity and through-thickness reinforcement (D11
`and Ko,1996).
`-
`Three-dimensional knitted fabrics are produced by weft or warp knitting.
`An example of a weft knit"1s the near—net—shape structure knitted under
`computer control by the pressure foot process. In a collapsed form this
`preform has been used for carbon—carbon aircraft brakes. While weft-
`knitte'd structures have applications in limited areas, multiaxial warp knit
`(MWK) 3—D structures are more promising and have undergone a great
`deal of development in recent years. MWK fabrics generally possess up to
`four different load—bearing yarn systems alranged so that each can take on
`stress and strain virtuallyin all directions. Since these load-bearing yarns
`lie straightin the fabric,with no crimp, the physical parameters of_the indi-
`vrdual