Three-dimensional knitted fabric manufacturers knitted fabrics have been widely used in many fields, especially in technical textiles. The development of 3D knitted fabrics is based on 2D knitted fabrics. However, while a considerable amount of research has been performed on knitted fabrics, by comparison little is known about the mechanical properties and applications of 3D knitted fabrics. This chapter provides a description of the three types of knitted fabrics currently available, which are broadly categorized as multiaxial warp-knitted fabrics, space fabrics or sandwich fabrics, and 3D knitted fabrics or near-net-shaped knitted fabrics. The structures, properties, production, and applications of these different 3D knitted fabrics are described separately.Knitted fabrics are subdivided into warp and weft knitted fabrics. Both types of fabric consist of intertwined loops. Knitted fabrics usually possess high elasticity due to their loop structure.
The difference between the two knitting processes is the formation of the loops. The loops of the warp knitting process are formed in rows in production direction through collectively moved needles. The loops of the weft knitting process are formed orthogonal to the production direction through individually moved needles. The basic structure of warp and weft knitted fabrics is shown in Fig. Knitted fabric is unique in that it possesses a high order of elasticity and recovery. Unlike woven fabric, which possesses a low degree of elongation, knitted fabric can be stretched to a considerable length and yet, when it is released, it will gradually return to its original shape and configuration. It is this feature of the fabric, plus the air permeability arising from its looped structure, that imparts to it the following properties: a high degree of wrinkle resistance knitted apparel generally requires little ironing good drape; a high degree of comfort; a porous nature allowing the skin to breathe freely; and elasticity allowing freedom of movement.Knitted fabrics are categorised as either constructed.
Of the two, the faster and the more economical to produce is the weft-knitted fabric that can be accomplished with a single package of yarn. The warp-knitting process, however, requires a warp beam, i.e., a running sheet of yarns as does the weaving process. Loops are formed transversely in the case of the weft knitting and essentially vertically in the case of the warp knitting . Simplest or plain weft knits tend to be very extensible and dimensionally unstable. One could improve on these tendencies by using additional yarns that interlock the loops. In contrast, the warp-knitted structures are basically more interlocked and dimensionally highly stable. The knitted fabrics are more flexible, compliant and conformable than are the woven fabrics, and one of them, the warp, also does not unravel as easily when cut to fit an application. A major limitation of knitted fabrics in some applications is porosity, which, owing to the nature of the loop structure, tends to be high. The knitted nets and bandages can be draped more effectively than the woven materials over areas that require three-dimensional conformability.
One of the primary applications of knitted structures in wound care is in compression hosiery used for treatment of venous stasis.In a warp-knitting process, simultaneous yarn-feeding and loop-forming actions occur at every needle in the needle bar during the same knitting cycle Spencer, 2001. The main difference from weft-knitted structures consists of the fact that all working needles on warp-knitting machines move simultaneously and, consequently, the loops are formed in a row simultaneously. Loop structures are formed in the warp yarn system in the length direction of the fabric. Thus, during one revolution of the shaft of the warp machine, from a few tens up to thousands of loops are formed. Warp-knitting features substantially higher performance compared with weft-knitting. In contrast to weft-knitted fabrics, warp-knitted fabrics find widespread use in the reinforcement of various composite materials, including those for civil engineering applications. Manufacturing technology for warp-knitted fabrics combines the benefits of weaving and knitting. Similar to weaving, yarns are wound from warp beams, and are located in the fabric in two perpendicular directions. In the manufacture of technical fabrics, directly oriented warp- and weft-reinforcing, high-strength yarns are inserted to provide the necessary mechanical characteristics and dimensional stability of the fabric. The reinforcing yarns are then combined with warp-knitting yarns.
