1 3-D textile reinforcements in composite materials FRANK K.KO 1.1 Introduction Textile structures are known for their unique combination of light weight and flexibility and their ability to offer a combination of strength and toughness.Textile structures have long been recognized as an attractive reinforcement form for applications ranging from aircraft wings produced by Boeing Aircraft Co.in the 1920s to carbon-carbon nose cones produced by General Electric in the 1950s.Textile preforms are fibrous assemblies with prearranged fiber orientation preshaped and often preimpregnated with matrix for composite formation.The microstructural organization fibers within a preform,or fiber architecture,determines the pore geome- try,pore distribution and tortuosity of the fiber paths within a composite. Textile preforms not only play a key role in translating fiber properties to 、兰 composite performance but also influence the ease or difficulty in matrix infiltration and consolidation.Textile preforms are the structural backbone for the toughening and net shape manufacturing of composites When combined with high-performance fibers,matrices and properly tailored fiber/matrix interfaces,the creative use of fiber architecture promises to expand the design options for strong and tough structural composites. Of the large family of textile structures,3-D fabrics have attracted the most serious interest in the aerospace industry and served as a catalyst in stimulating the revival of interest in textile composites.3-D fabrics for structural composites are fully integrated continuous fiber assemblies having multiaxial in-plane and out-of-plane fiber orientation.More specifi- cally,a 3-D fabric is one that is fabricated by a textile process,resulting in three or more yarn diameters in the thickness direction with fibers oriented in three orthogonal planes.The engineering application of 3-D composite has its origin in aerospace carbon-carbon composites.3-D fabrics for composites date back to the 1960s,responding to the needs in the emerging aerospace industry for parts and structures that were capable of 9
1.1 Introduction Textile structures are known for their unique combination of light weight and flexibility and their ability to offer a combination of strength and toughness. Textile structures have long been recognized as an attractive reinforcement form for applications ranging from aircraft wings produced by Boeing Aircraft Co. in the 1920s to carbon–carbon nose cones produced by General Electric in the 1950s. Textile preforms are fibrous assemblies with prearranged fiber orientation preshaped and often preimpregnated with matrix for composite formation. The microstructural organization of fibers within a preform, or fiber architecture, determines the pore geometry, pore distribution and tortuosity of the fiber paths within a composite. Textile preforms not only play a key role in translating fiber properties to composite performance but also influence the ease or difficulty in matrix infiltration and consolidation. Textile preforms are the structural backbone for the toughening and net shape manufacturing of composites. When combined with high-performance fibers, matrices and properly tailored fiber/matrix interfaces, the creative use of fiber architecture promises to expand the design options for strong and tough structural composites. Of the large family of textile structures, 3-D fabrics have attracted the most serious interest in the aerospace industry and served as a catalyst in stimulating the revival of interest in textile composites. 3-D fabrics for structural composites are fully integrated continuous fiber assemblies having multiaxial in-plane and out-of-plane fiber orientation. More specifi- cally, a 3-D fabric is one that is fabricated by a textile process, resulting in three or more yarn diameters in the thickness direction with fibers oriented in three orthogonal planes. The engineering application of 3-D composite has its origin in aerospace carbon–carbon composites. 3-D fabrics for composites date back to the 1960s, responding to the needs in the emerging aerospace industry for parts and structures that were capable of 1 3-D textile reinforcements in composite materials FRANK K. KO 9 RIC1 7/10/99 7:15 PM Page 9 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:29:37 AM IP Address: 158.132.122.9
10 3-D textile reinforcements in composite materials withstanding multidirectional mechanical stresses and thermal stresses. Since most of these early applications were for high-temperature and ablative environments,carbon-carbon composites were the principal mate- rials.As indicated in a review article by McAllister and Lachman [1],the early carbon-carbon composites were reinforced by biaxial (2-D)fabrics. Beginning in the early 1960s,it took almost a whole decade and the trial of numerous reinforcement concepts,including needled felts,pile fabrics and stitched fabrics,to recognize the necessity of 3-D fabric reinforcements to address the problem of poor interlaminar strength in carbon-carbon composites [2-4].Although the performance of a composite depends a great deal on the type of matrix and the nature of the fiber-matrix inter- face,it appears that much can be learned from the experience of the role of fiber architecture in the processing and performance of carbon-carbon composites. The expansion of global interest in recent years in 3-D fabrics for resin, metal and ceramic matrix composites is a direct result of the current trend pooM in the expansion of the use of composites from secondary to primary load-bearing applications in automobiles,building infrastructures,surgical implants,aircraft and space structures.This requires a substantial improve- 防 ment in the through-the-thickness strength,damage tolerance and reliabil- ity of composites.In addition,it is also desirable to reduce the cost and broaden the usage of composites from aerospace to automotive applica- tions.This calls for the development of a capability for quantity production and the direct formation of structural shapes.In order to improve the damage tolerance of composites,a high level of through-thickness and interlaminar strength is required.The reliability of a composite depends on the uniform distribution of the materials and consistency of interfacial properties.The structural integrity and handleability of the reinforcing material for the composite is critical for large-scale,automated production. A method for the direct formation of the structural shapes would therefore greatly simplify the laborious hand lay-up composite formation process. With the experience gained in the 3-D carbon-carbon composites and the recent progress in fiber technology and computer-aided textile design and liquid molding technology,the class of 3-D fabric structures is increasingly being recognized as serious candidates for structural composites. The importance of 3-D fabric reinforced composites in the family of textile structural composites is reflected in several recent books on the subject [5,6.This chapter is intended to provide an introduction to 3-D textile reinforcements for composites.The discussion will focus on the pre- forming process and structural geometry of the four basic classes of inte- grated fiber architecture:woven,knit and braid,and orthogonal non-woven 3-D structure
withstanding multidirectional mechanical stresses and thermal stresses. Since most of these early applications were for high-temperature and ablative environments, carbon–carbon composites were the principal materials. As indicated in a review article by McAllister and Lachman [1], the early carbon–carbon composites were reinforced by biaxial (2-D) fabrics. Beginning in the early 1960s, it took almost a whole decade and the trial of numerous reinforcement concepts, including needled felts, pile fabrics and stitched fabrics, to recognize the necessity of 3-D fabric reinforcements to address the problem of poor interlaminar strength in carbon–carbon composites [2–4]. Although the performance of a composite depends a great deal on the type of matrix and the nature of the fiber–matrix interface, it appears that much can be learned from the experience of the role of fiber architecture in the processing and performance of carbon–carbon composites. The expansion of global interest in recent years in 3-D fabrics for resin, metal and ceramic matrix composites is a direct result of the current trend in the expansion of the use of composites from secondary to primary load-bearing applications in automobiles, building infrastructures, surgical implants, aircraft and space structures. This requires a substantial improvement in the through-the-thickness strength, damage tolerance and reliability of composites. In addition, it is also desirable to reduce the cost and broaden the usage of composites from aerospace to automotive applications. This calls for the development of a capability for quantity production and the direct formation of structural shapes. In order to improve the damage tolerance of composites, a high level of through-thickness and interlaminar strength is required. The reliability of a composite depends on the uniform distribution of the materials and consistency of interfacial properties. The structural integrity and handleability of the reinforcing material for the composite is critical for large-scale, automated production. A method for the direct formation of the structural shapes would therefore greatly simplify the laborious hand lay-up composite formation process. With the experience gained in the 3-D carbon–carbon composites and the recent progress in fiber technology and computer-aided textile design and liquid molding technology, the class of 3-D fabric structures is increasingly being recognized as serious candidates for structural composites. The importance of 3-D fabric reinforced composites in the family of textile structural composites is reflected in several recent books on the subject [5,6]. This chapter is intended to provide an introduction to 3-D textile reinforcements for composites. The discussion will focus on the preforming process and structural geometry of the four basic classes of integrated fiber architecture: woven, knit and braid, and orthogonal non-woven 3-D structure. 10 3-D textile reinforcements in composite materials RIC1 7/10/99 7:15 PM Page 10 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:29:37 AM IP Address: 158.132.122.9
3-D textile reinforcements in composite materials Table 1.1.Fiber architecture for composites Level Reinforcement Textile Fiber length Fiber Fiber system construction orientation entanglement Discrete Chopped fiber Discontinuous Uncontrolled None Linear Filament yarn Continuous Linear None 0 Laminar Simple fabric Continuous Planar Planar V Integrated Advanced fabric Continuous 3-D 3-D 1.2 Classification of textile preforms There is a large family of textile preforming methods suitable for composite manufacturing [7].The key criteria for the selection of textile preforms for structural composites are (a)the capability for in-plane multiaxial reinforcement,(b)through-thickness reinforcement and(c)the capability for formed shape and/or net shape manufacturing.Depending on the pro- cessing and end use requirements some or all of these features are required. On the basis of structural integrity and fiber linearity and continuity,fiber architecture can be classified into four categories:discrete,continuous, planar interlaced (2-D)and fully integrated (3-D)structures.In Table 1.1 the nature of the various levels of fiber architecture is summarized [8]. A discrete fiber system such as a whisker or fiber mat has no material continuity;the orientation of the fibers is difficult to control precisely, although some aligned discrete fiber systems have recently been intro- duced.The structural integrity of the fibrous preform is derived mainly from 具 interfiber friction.The strength translation efficiency,or the fraction of fiber strength translated to the non-aligned fibrous assembly of the reinforce- ment system,is quite low. The second category of fiber architecture is the continuous filament,or unidirectional(0)system.This architecture has the highest level of fiber continuity and linearity,and consequently has the highest level of property translation efficiency and is very suitable for filament wound and angle ply tape lay-up structures.The drawback of this fiber architecture is its intra- and interlaminar weakness owing to the lack of in-plane and out-of-plane yarn interlacings. A third category of fiber reinforcement is the planar interlaced and inter- looped system.Although the intralaminar failure problem associated with the continuous filament system is addressed with this fiber architecture,the interlaminar strength is limited by the matrix strength owing to the lack of through-thickness fiber reinforcement. The fully integrated system forms the fourth category of fiber architec- ture wherein the fibers are oriented in various in-plane and out-of-plane
1.2 Classification of textile preforms There is a large family of textile preforming methods suitable for composite manufacturing [7]. The key criteria for the selection of textile preforms for structural composites are (a) the capability for in-plane multiaxial reinforcement, (b) through-thickness reinforcement and (c) the capability for formed shape and/or net shape manufacturing. Depending on the processing and end use requirements some or all of these features are required. On the basis of structural integrity and fiber linearity and continuity, fiber architecture can be classified into four categories: discrete, continuous, planar interlaced (2-D) and fully integrated (3-D) structures. In Table 1.1 the nature of the various levels of fiber architecture is summarized [8]. A discrete fiber system such as a whisker or fiber mat has no material continuity; the orientation of the fibers is difficult to control precisely, although some aligned discrete fiber systems have recently been introduced.The structural integrity of the fibrous preform is derived mainly from interfiber friction.The strength translation efficiency, or the fraction of fiber strength translated to the non-aligned fibrous assembly of the reinforcement system, is quite low. The second category of fiber architecture is the continuous filament, or unidirectional (0°) system. This architecture has the highest level of fiber continuity and linearity, and consequently has the highest level of property translation efficiency and is very suitable for filament wound and angle ply tape lay-up structures. The drawback of this fiber architecture is its intraand interlaminar weakness owing to the lack of in-plane and out-of-plane yarn interlacings. A third category of fiber reinforcement is the planar interlaced and interlooped system. Although the intralaminar failure problem associated with the continuous filament system is addressed with this fiber architecture, the interlaminar strength is limited by the matrix strength owing to the lack of through-thickness fiber reinforcement. The fully integrated system forms the fourth category of fiber architecture wherein the fibers are oriented in various in-plane and out-of-plane 3-D textile reinforcements in composite materials 11 Table 1.1. Fiber architecture for composites Level Reinforcement Textile Fiber length Fiber Fiber system construction orientation entanglement I Discrete Chopped fiber Discontinuous Uncontrolled None II Linear Filament yarn Continuous Linear None III Laminar Simple fabric Continuous Planar Planar IV Integrated Advanced fabric Continuous 3-D 3-D RIC1 7/10/99 7:15 PM Page 11 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:29:37 AM IP Address: 158.132.122.9
12 3-D textile reinforcements in composite materials 1c. 1h. 1.1 The Noveltex@method. WV LE:6Z directions.With the continuous filament yarn,a 3-D network of yarn bundles is formed in an integral manner.The most attractive feature of the 9 integrated structure is the additional reinforcement in the through-thick- A ness direction which makes the composite virtually delamination-free. Another interesting aspect of many of the fully integrated structures such as 3-D woven,knits,braids and non-wovens is their ability to assume complex structural shapes. Another way of classifying textile preforms is based on the fabric for- mation techniques.The conversion of fiber to preform can be accomplished via the 'fiber to fabric'(FTF)process,the'yarn to fabric'(YTF)process and combinations of the two.An example of the FTF process is the Noveltex method developed by P.Olry at SEP(Societe Europeenne de Propulsion, Bordeaux,France)[9].As shown in Fig.1.1,the Noveltex concept is based on the entanglement of fiber webs by needle punching.A similar process is being developed in Japan by Fukuta [10]using fluid jets in place of the needles to create through-thickness fiber entanglement. The YTF processes are popular means for preform fabrication wherein the linear fiber assemblies (continuous filament)or twisted short fiber (staple)assemblies are interlaced,interlooped or intertwined to form 2-D or 3-D fabrics.Examples of preforms created by the YTF processes are shown in Fig.1.2.A comparison of the basic YTF processes is given in Table 1.2. In addition to the FTF and YTF processes,textile preforms can be fabricated by combining structure and process.For example,the FTF webs
directions. With the continuous filament yarn, a 3-D network of yarn bundles is formed in an integral manner. The most attractive feature of the integrated structure is the additional reinforcement in the through-thickness direction which makes the composite virtually delamination-free. Another interesting aspect of many of the fully integrated structures such as 3-D woven, knits, braids and non-wovens is their ability to assume complex structural shapes. Another way of classifying textile preforms is based on the fabric formation techniques. The conversion of fiber to preform can be accomplished via the ‘fiber to fabric’ (FTF) process, the ‘yarn to fabric’ (YTF) process and combinations of the two. An example of the FTF process is the Noveltex® method developed by P. Olry at SEP (Société Européenne de Propulsion, Bordeaux, France) [9]. As shown in Fig. 1.1, the Noveltex concept is based on the entanglement of fiber webs by needle punching. A similar process is being developed in Japan by Fukuta [10] using fluid jets in place of the needles to create through-thickness fiber entanglement. The YTF processes are popular means for preform fabrication wherein the linear fiber assemblies (continuous filament) or twisted short fiber (staple) assemblies are interlaced, interlooped or intertwined to form 2-D or 3-D fabrics. Examples of preforms created by the YTF processes are shown in Fig. 1.2.A comparison of the basic YTF processes is given in Table 1.2. In addition to the FTF and YTF processes, textile preforms can be fabricated by combining structure and process. For example, the FTF webs 12 3-D textile reinforcements in composite materials 1.1 The Noveltex® method. RIC1 7/10/99 7:15 PM Page 12 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:29:37 AM IP Address: 158.132.122.9
3-D textile reinforcements in composite materials 13 Biaxial High modulus Multilayer Triaxial Tubular Tubular braid woven woven woven woven braid laid in warp 远说 Weft knit Weft knit Weft knit Square Square braid Weft knit laid in weft laid in warp laid in weft braid laid in warp laid in warp 敢理刀 D Warp knit Warp knit Weft inserted Weft inserted XD Stitchbonded warp knit warp knit wo'ssaudmau'praypoow//:dny Aq laid in warp laid in warp laid in warp 2L-10e Biaxial XYZ Flat braid Flat braid 3-D braid 3-D braid bonded laid in system laid in warp laid in warp 1.2 Examples of yarn-to-fabric preforms. Table 1.2.A comparison of yarn-to-fabric formation techniques YTF processes Basic direction of Basic formation technique yarn introduction Weaving Tw0(0°/90) Interlacing (by selective warp and fill insertion of90°yarns into0°yarn system Braiding One (machine Intertwining (position displacement) direction) Knitting 0ne(0°or90y Interlooping (by drawing warp or fill loops of yarns over previous loops) Nonwoven Three or more Mutual fiber placement (orthogonal)
3-D textile reinforcements in composite materials 13 Biaxial woven High modulus woven Multilayer woven Triaxial woven Tubular braid Tubular braid laid in warp Weft knit Weft knit laid in weft Weft knit laid in warp Weft knit laid in weft laid in warp Square braid Square braid laid in warp Stitchbonded laid in warp XD Weft inserted warp knit laid in warp Weft inserted warp knit Warp knit laid in warp Warp knit Biaxial bonded XYZ laid in system Flat braid Flat braid laid in warp 3-D braid 3-D braid laid in warp 1.2 Examples of yarn-to-fabric preforms. Table 1.2. A comparison of yarn-to-fabric formation techniques YTF processes Basic direction of Basic formation technique yarn introduction Weaving Two (0°/90°) Interlacing (by selective warp and fill insertion of 90° yarns into 0° yarn system Braiding One (machine Intertwining (position displacement) direction) Knitting One (0° or 90°) Interlooping (by drawing warp or fill loops of yarns over previous loops) Nonwoven Three or more Mutual fiber placement (orthogonal) RIC1 7/10/99 7:15 PM Page 13 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:29:37 AM IP Address: 158.132.122.9
14 3-D textile reinforcements in composite materials Eight9-p时elements Basic 9-ply subelement Stiffener AS4/3501 1/2-in.stitch spacing Eight 9-ply segments stitched with 200d Kevlar to form blade Stiffened panel Skin Fold blade web ends open Stitching head Holding pin Six 9-ply segments Stringer flanges stitched to skin Web locating bar Gde bar- Folding frame able top .Stitched flap on skin 1.3 Combination of FTF and YTF processes. WV LE:6Z can be incorporated into a YTF preform by needle or fluid jet entangle- ment to provide through-the-thickness reinforcement.Sewing is another 2102 example that can combine or strategically join FTF and/or YTF fabrics together to create a preform having multidirectional fiber reinforcement [11](Fig.1.3). 个物鸡 1.3 Structural geometry of 3-D textiles The structural geometry of 3-D textiles can be characterized at both the macroscopic and the microscopic levels.At the macroscopic level,the exter- nal shape and the internal cellular structures are the result of a particular textile process and fabric construction employed in the creation of the structure.Similar shape and cellular geometry may be created by different textile processes.For example,a net shape I-beam can be produced by a weaving,braiding or knitting process.However,the microstructure or the fiber architecture produced by these three processes are quite different. This will lead to different levels of translation efficiency of the inherent fiber properties to the composite as well as different levels of damage-resistant characteristics.The efficient translation of fiber properties to the com- posite depends on the judicious selection of fiber architecture which is gov- erned by the directional concentration of fibers.This directional fiber con- centration can be quantified by fiber volume fraction Vr and fiber orientation,0.Depending upon the textile manufacturing process used and the type of fabric construction,families of Vr-0 functions can be gener- ated.These Vr-0 functions can be developed by geometrical modeling as
can be incorporated into a YTF preform by needle or fluid jet entanglement to provide through-the-thickness reinforcement. Sewing is another example that can combine or strategically join FTF and/or YTF fabrics together to create a preform having multidirectional fiber reinforcement [11] (Fig. 1.3). 1.3 Structural geometry of 3-D textiles The structural geometry of 3-D textiles can be characterized at both the macroscopic and the microscopic levels.At the macroscopic level, the external shape and the internal cellular structures are the result of a particular textile process and fabric construction employed in the creation of the structure. Similar shape and cellular geometry may be created by different textile processes. For example, a net shape I-beam can be produced by a weaving, braiding or knitting process. However, the microstructure or the fiber architecture produced by these three processes are quite different. This will lead to different levels of translation efficiency of the inherent fiber properties to the composite as well as different levels of damage-resistant characteristics. The efficient translation of fiber properties to the composite depends on the judicious selection of fiber architecture which is governed by the directional concentration of fibers. This directional fiber concentration can be quantified by fiber volume fraction Vf and fiber orientation, q. Depending upon the textile manufacturing process used and the type of fabric construction, families of Vf - q functions can be generated. These Vf - q functions can be developed by geometrical modeling as 14 3-D textile reinforcements in composite materials Eight 9-ply elements 1/2-in. stitch spacing Basic 9-ply subelement AS4/3501 Stiffener Eight 9-ply segments stitched with 200d Kevlar to form blade Stiffened panel Skin Fold blade web ends open Stitching head Holding pin Web locating bar Glide bar Folding frame Panel Table top Stitched flap on skin Six 9-ply segments Stringer flanges stitched to skin 0° +45° 0° +45° 0° +45° 0° –45° 90° 1.3 Combination of FTF and YTF processes. RIC1 7/10/99 7:15 PM Page 14 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:29:37 AM IP Address: 158.132.122.9
3-D textile reinforcements in composite materials 15 a b 1.4 3-D woven fabrics. detailed by Ko and Du [12].Accordingly,the structure-property relation- ship of 3-D textile composites is a result of the dynamic interaction of microstructural and macrostructural geometries.In this section,the struc- tural shapes,cellular structures and fiber architectures expressed in terms 2-10 of the Vr-0 functions are presented for the four basic classes of 3-D textile reinforcements. 1.3.1 3-D woven fabrics 3-D woven fabrics are produced principally by the multiple-warp weaving method which has long been used for the manufacturing of double and triple cloths for bags,webbings and carpets.By the weaving method,various fiber architectures can be produced including solid orthogonal panels (Fig.1.4a),variable thickness solid panels(Fig.1.4b,c),and core structures simulating a box beam (Fig.1.4d)or a truss-like structure (Fig.1.4e). Furthermore,by proper manipulation of the warp yarns,as exemplified by the angle interlock structure (Fig.1.4f),the through-thickness yarns can be organized into a diagonal pattern.To address the inherent lack of in- plane reinforcement in the bias direction,Dow [13]modified the triaxial weaving technology to produce multilayer triaxial fabrics as shown in Fig.1.4(g). Through unit cell geometric modeling the Vr-0 functions can be gener- ated for various woven fabrics.Figure 1.5 plots total fiber volume fraction versus web interlock angle for an angle interlock 3-D woven fabric,with three levels of linear density ratio.For purposes of calculation,the fiber packing fraction is assumed to be 0.8,which provides the upper limit for possible fiber volume fraction.The fabric tightness factor(n)used is 0.2
detailed by Ko and Du [12]. Accordingly, the structure–property relationship of 3-D textile composites is a result of the dynamic interaction of microstructural and macrostructural geometries. In this section, the structural shapes, cellular structures and fiber architectures expressed in terms of the Vf - q functions are presented for the four basic classes of 3-D textile reinforcements. 1.3.1 3-D woven fabrics 3-D woven fabrics are produced principally by the multiple-warp weaving method which has long been used for the manufacturing of double and triple cloths for bags, webbings and carpets. By the weaving method, various fiber architectures can be produced including solid orthogonal panels (Fig. 1.4a), variable thickness solid panels (Fig. 1.4b, c), and core structures simulating a box beam (Fig. 1.4d) or a truss-like structure (Fig. 1.4e). Furthermore, by proper manipulation of the warp yarns, as exemplified by the angle interlock structure (Fig. 1.4f), the through-thickness yarns can be organized into a diagonal pattern. To address the inherent lack of inplane reinforcement in the bias direction, Dow [13] modified the triaxial weaving technology to produce multilayer triaxial fabrics as shown in Fig. 1.4(g). Through unit cell geometric modeling the Vf - q functions can be generated for various woven fabrics. Figure 1.5 plots total fiber volume fraction versus web interlock angle for an angle interlock 3-D woven fabric, with three levels of linear density ratio. For purposes of calculation, the fiber packing fraction is assumed to be 0.8, which provides the upper limit for possible fiber volume fraction. The fabric tightness factor (h) used is 0.2. 3-D textile reinforcements in composite materials 15 1.4 3-D woven fabrics. RIC1 7/10/99 7:15 PM Page 15 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:29:37 AM IP Address: 158.132.122.9
16 3-D textile reinforcements in composite materials 1.0 0.9 Fiber packing in yarn 0.8 0.7 1.0 0.6 0.5 0.5 0.4 0.3 入we/0M=0.1 0.2 0.1 0.0 10 20 30 405060 7080 90 6() 1.5 Process window of fiber volume fraction for 3-D woven (%whe wo'ssaidmau'peaypoo/:dny WV LE:6Z is linear density of warp or web yarn,Ar is linear density of filled yarn). 210e 1.3.2 Orthogonal non-woven fabrics Pioneered by aerospace companies such as General Electric [14],the non- woven 3-D fabric technology was developed further by Fiber Materials Incorporated [15].Recent progress in automation of the non-woven 3-D fabric manufacturing process was made in France by Aerospatiale [16],SEP [9]and Brochier [17,18]and in Japan by Fukuta and Coworkers [19,20]. The structural geometries resulting from the various processing tech- niques are shown in Fig.1.6.Figure 1.6(a)and (b)show the single bundle XYZ fabrics in a rectangular and cylindrical shape.In Fig.1.6(b),the mul- tidirectional reinforcement in the plane of the 3-D structure is shown. Although most of the orthogonal non-woven 3-D structures consist of linear yarn reinforcements in all of the directions,introduction of the planar yarns in a non-linear manner,as shown in Fig.1.6(c),(d)and (e)can result in an open lattice or a flexible and conformable structure. Based on the unit cell geometry shown in Fig.1.7,assuming an orthogo- nal placement of yarns in all three directions,the Vr-0 function was con- structed for an orthogonal woven fabric.Figure 1.8 plots the fiber volume fraction versus d,/d,(fiber diameter)ratios,assuming a fiber packing frac- tion of 0.8.For all three levels of d,/d,ratios,the fiber volume fraction first decreases with the increase in d/d,ratio,reaches a minimum,and then increases.As can be seen in the figure,the maximum fiber volume fraction is about 0.63 at either high or low d/d ratios,whereas the minimum fiber
1.3.2 Orthogonal non-woven fabrics Pioneered by aerospace companies such as General Electric [14], the nonwoven 3-D fabric technology was developed further by Fiber Materials Incorporated [15]. Recent progress in automation of the non-woven 3-D fabric manufacturing process was made in France by Aérospatiale [16], SEP [9] and Brochier [17,18] and in Japan by Fukuta and Coworkers [19,20]. The structural geometries resulting from the various processing techniques are shown in Fig. 1.6. Figure 1.6(a) and (b) show the single bundle XYZ fabrics in a rectangular and cylindrical shape. In Fig. 1.6(b), the multidirectional reinforcement in the plane of the 3-D structure is shown. Although most of the orthogonal non-woven 3-D structures consist of linear yarn reinforcements in all of the directions, introduction of the planar yarns in a non-linear manner, as shown in Fig. 1.6(c), (d) and (e) can result in an open lattice or a flexible and conformable structure. Based on the unit cell geometry shown in Fig. 1.7, assuming an orthogonal placement of yarns in all three directions, the Vf - q function was constructed for an orthogonal woven fabric. Figure 1.8 plots the fiber volume fraction versus dy/dx (fiber diameter) ratios, assuming a fiber packing fraction of 0.8. For all three levels of dz/dx ratios, the fiber volume fraction first decreases with the increase in dy/dx ratio, reaches a minimum, and then increases. As can be seen in the figure, the maximum fiber volume fraction is about 0.63 at either high or low dy/dx ratios, whereas the minimum fiber 16 3-D textile reinforcements in composite materials 1.5 Process window of fiber volume fraction for 3-D woven (l w/q is linear density of warp or web yarn, lf is linear density of filled yarn). RIC1 7/10/99 7:15 PM Page 16 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:29:37 AM IP Address: 158.132.122.9
3-D textile reinforcements in composite materials 17 wo'ssaudmau 'peaypoom//:dny Aq d 1.6 Orthogonal woven fabrics. 'I'EI'85I :ssappy dl 1.7 Unit cell for orthogonal non-woven fabrics. volume fraction of about 0.47 is achieved when both d/d,and d/d ratios are equal to 1. 1.3.3 Knitted 3-D fabrics The knitted 3-D fabrics are produced by either the weft knitting or warp knitting process.An example of a weft knit is the near net shape structure
volume fraction of about 0.47 is achieved when both dy/dx and dy/dx ratios are equal to 1. 1.3.3 Knitted 3-D fabrics The knitted 3-D fabrics are produced by either the weft knitting or warp knitting process. An example of a weft knit is the near net shape structure 3-D textile reinforcements in composite materials 17 1.6 Orthogonal woven fabrics. 1.7 Unit cell for orthogonal non-woven fabrics. RIC1 7/10/99 7:15 PM Page 17 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:29:37 AM IP Address: 158.132.122.9
18 3-D textile reinforcements in composite materials 0.65 100 0.01 0.60 0.55 0.50 Minimum fiber volume fraction 0.45 1010102101001010210310 dyd. 1.8 Process window of fiber volume fraction for orthogonal non- woven fabrics. knitted by the Pressure Foot process [21](Fig.1.9a).In a collapsed form this preform has been used for carbon-carbon aircraft brakes.The unique feature of the weft knit structures is their conformability [22].By strategic introduction of linear reinforcement yarns,weft knitted structures can be used effectively for forming very complex shape structures.While the suit- ability of weft knit for structural applications is still being evaluated,much A progress has been made in the multiaxial warp knit(MWK)technology in recent years [23,24].From the structural geometry point of view,the MWK fabric systems consist of warp (0),weft (90)and bias (t0)yarns held together by a chain or tricot stitch through the thickness of the fabric,as illustrated in Fig.1.10(b).The logical extension of the MWK technology is the formation of circular multiaxial structures by the warp knitting process. This technology (Fig.1.9d)has been demonstrated in the Institute of Tex- tiles of the University of Aachen [25]. An example of MWK is the LIBA system,as shown in Fig.1.9(c)and(d). Six layers of linear yarns can be assembled in various stacking sequences along with a fiber mat and can be integrated together by knitting needles piercing through the yarn layers. The unit cell geometric analysis of a four-layer system is used as an example to generate the Vr-0 functions for the MWK fabric [26].This analysis can be generalized to include other MWK systems with six or more layers of insertion yarns.The fiber volume fraction relation in Fig.1.10 shows that for the fixed parameters selected,only a limited window exists for the MWK fabric construction.The window is bounded by two factors: yarn jamming and the point of 90 bias yarn angle.Fabric constructions cor- responding to the curve marked'jamming'are at their tightest allowable point,and constructions at the 0->90 curve have the most open structure
knitted by the Pressure Foot® process [21] (Fig. 1.9a). In a collapsed form this preform has been used for carbon–carbon aircraft brakes. The unique feature of the weft knit structures is their conformability [22]. By strategic introduction of linear reinforcement yarns, weft knitted structures can be used effectively for forming very complex shape structures. While the suitability of weft knit for structural applications is still being evaluated, much progress has been made in the multiaxial warp knit (MWK) technology in recent years [23,24]. From the structural geometry point of view, the MWK fabric systems consist of warp (0°), weft (90°) and bias (±q) yarns held together by a chain or tricot stitch through the thickness of the fabric, as illustrated in Fig. 1.10(b). The logical extension of the MWK technology is the formation of circular multiaxial structures by the warp knitting process. This technology (Fig. 1.9d) has been demonstrated in the Institute of Textiles of the University of Aachen [25]. An example of MWK is the LIBA system, as shown in Fig. 1.9(c) and (d). Six layers of linear yarns can be assembled in various stacking sequences along with a fiber mat and can be integrated together by knitting needles piercing through the yarn layers. The unit cell geometric analysis of a four-layer system is used as an example to generate the Vf - q functions for the MWK fabric [26]. This analysis can be generalized to include other MWK systems with six or more layers of insertion yarns. The fiber volume fraction relation in Fig. 1.10 shows that for the fixed parameters selected, only a limited window exists for the MWK fabric construction. The window is bounded by two factors: yarn jamming and the point of 90° bias yarn angle. Fabric constructions corresponding to the curve marked ‘jamming’ are at their tightest allowable point, and constructions at the q Æ90° curve have the most open structure. 18 3-D textile reinforcements in composite materials 1.8 Process window of fiber volume fraction for orthogonal nonwoven fabrics. RIC1 7/10/99 7:15 PM Page 18 Copyrighted Material downloaded from Woodhead Publishing Online Delivered by http://woodhead.metapress.com Hong Kong Polytechnic University (714-57-975) Saturday, January 22, 2011 12:29:37 AM IP Address: 158.132.122.9
