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