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 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 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￾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. 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