Knitted fabric reinforcement weft knit

Ramakrishna S. Characterization and modeling of the tensile properties of plain weft-knit fabric-reinforced composites. Compos Sci Tech 1997 57 1-22. 

Rios CR, Ogin SL, Lekakou C, Leong KH. A study of damage development in a weft knitted fabric reinforced composite part 1 - experiments using model sandwich laminates. Compos Appl Sci Ma /2007 38(7) 1173-793. 

X. Li, and S. Bai, Sheet forming of the multy-layered biaxial weft knitted fabric reinforcement. Part 1 On hemispherical surfaces. Compos. A 40, 766-777 (2009). 

S. D. Pandita, D. Falconet, I. Verpoest (2002) Impact properties of weft knitted fabric reinforced composites, Compos. Sci. Technol. 62,1113. 

The weft-knitting process has a loop formation perpendicular to the production direction. Therefore one yarn system is sufficient for the manufacturing of weft-knitted fabrics. In weft-knitted NCF, reinforcing threads are fixed within the loops (Fig. 8.15). 

Wang Y, Gowayed Y, Kong X, Li J, Zhao D. Properties and analysis of composites reinforced with E-glass weft-knitted fabrics. J Compos Tech Res 1995 17 283-8. 

Three dimensional structures of multiaxial warp knitted fabrics have been recently developed for multidirectional reinforcement of composites. Multilayers of linear yams are assembled in warp (0°), weft (90°) and bias ( 0) directions to provide in-plane reinforcement in specific directions and they are stitched together by knitting yams to provide structural integrity and through the thickness reinforcement [1,2,3,4,5]. 

The precursor fiber type for reinforcing the carbon matrix can be an oxidized PAN fiber (opf), or either a PAN or pitch based carbon fiber. In some instances, for special applications, such as the Shuttle, a cellulose based carbon fiber is used. The reinforcements can be unidirectional have a random chopped fiber presentation as in a felt format a woven product from continuous fiber presented in a 2D, 3D, or in a Multi-D format (Section 21.1), or a non-woven carbon fiber. The chosen fiber architecture is most important for a given application and Lei et al [4] describe how, for example, 3-D braiding can be applied to carbon-carbon composites. One of the early forms of near net shape reinforcement used for carbon-carbon aircraft brakes was based on a weft knitted 3-D fabric made by the Pressure Foot process (Figure 14.1). 

For the production of composites, it is normally desired that textiles used for reinforcement possess great tensile strength and an extreme stiffness. The Young s modulus of textiles has to be significantly higher than that of the matrices used (for example, plastics). Conventional warp-knitted fabrics cannot fulfill these demands. Therefore, weft-reinforced, warp-knitted fabrics (Fig. 8.3) were developed to increase the stiffness of warp-knitted fabrics. 

Pillar (0°) threads and weft yarns are connected via warp knitting. When using a stiff material for the warp yarns, the spacer fabric can also be reinforced in the z-direction see Fig. 8.13. 

Weft-knitted NCF can be produced as biaxial and multiaxial fabrics or as two- and three-dimensional near-net-shape textile structures. Warp and weft threads out of rovings are superposed and fixed together with loop systems. Due to the course-wise weft insertion the reinforcing threads remain noncrimped. Through the combination of weft insertion over the entire width or part of the width with or without support of a stitch-transferring device and by changing loop sizes on individual needles, three-dimensional near-net-shape preforms can be produced (Hufenbach, 2007). 

Figure 13.18 Effect of the structure of the fabric on the load-deflection curve, in comparison with straight yarn reinforcement, (a) woven and short weft knit (b) weft insertion knit (after Peled and Bentur [44—46]).

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