Multiaxial warp knitted fabric

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]. 

Pastore CM, Whyte DW, Soebreto HB, Ko FK, Design and analysis of multiaxial warp knit fabrics for composites, J Ind Fabrics, 5(1), 84—91, Sep 1986. 

Figure 10.18 Application of microbraided yarn to textile, (a) Woven fabric, (b) flat braided fabric, (c) plain knitted fabric, and (d) multiaxial warp knitted fabric.

Fig. 1.3 Predicted and moduli for a range of reinforcement architectures 0 angle ply (for 0=0 to 45 to 90), cross-ply (0/90), eight-harness satin, and plain woven, triaxial woven fabric, braided (0=35° to 15°) and multiaxial warp knit ( - ), for the same fibre volume...

Multiaxial warp-knitted NCFs with noncourse-wise weft insertion consist of a current maximum of seven iayers of rovings or spread fiber tows oriented in paral-lei. The orientation of the single-fiber layers can be freely adjusted between -20 to +20° relative to the production direction (angle specification analogous to ENl 3473-1). On the top side of the fabric, an additional 0° layer can be attached. The introduction of two surface fabrics, for example nonwovens, is also possible (Fig. 8.10). The mass per unit area, the structure (closed or open) of the fabric, the material, and the thread count of each layer can be varied individually for each layer. The single-fiber layers are fixed together with a warp yarn. 

Mainly woven fabrics (Chapter 4) and nonwovens (Chapter 6) are used as geotextiles. Today also multiaxial structures such as multiaxial multi-ply warp-knitted fabrics (MAG) or stitch-bonded fabrics (NVG) (Chapter 7) are used more and more in this field of application. The yarns in this process are monofiles, filament yarns (Chapter 2), or spun yarns (Chapter 3). 

DOSs are unique multiply fabrics (Au, 2011). In these sfructures, straight ends of absolutely parallel and noncrimped yams are inserted into the stmctures at different angles (Raz, 1988). With these techniques, fabric properties can be engineered to enhance the in-plane properties only in the required orientations, thereby offering the produced fabric the ideal combination of excellent mechanical properties and cost-effective production. DOSs normally include mono-, bi-, tri-, and multiaxial stmctures, which can be produced with weft knitting or warp knitting technologies. 

Normally, the stresses of fiber-reinforced composite components are not mono- or biaxial. Therefore, for the use of biaxial textiles it is necessary to lay several layers in different orientations above one another to reinforce a component with regard to multiaxial loading. This procedure generates a large quantity of waste by cutting the layers in different orientations. It also increases the amount of time for the production of a composite component. Warp-knitted, multiaxial multi ply fabrics (MAG) were developed to eliminate the aforementioned disadvantages (Fig. 8.5). 

Warp-knitted, multiaxial multi-ply fabric, MAG (LIBA)... 

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). 

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