Mechanical and Impact Properties of Composite Laminates Reinforced with Kevlar Multiaxial Warp Knit Fabrics

The mechanical and impact properties of multiaxial warp knit fabric reinforced composite laminates have been studied. Kevlar® fibre was used to fabricate the multiaxial warp knit structure for unidirectional reinforcing as well as stitching yarns. Tensile, flexural, short beam shear, and impact properties have been compared with those of woven laminated composites. The results showed that increased interlaminar shear strength is the main characteristic feature of the multiaxial warp knit composite compared with plain woven laminates. The interlaminar shear strength of multiaxial warp knit composites showed up to 52% increase compared with that of woven laminates composites. Also the delamination was retarded due to the increase in interlaminar shear strength of the multiaxial warp knit composites. It is shown that the through-the-thickness reinforcing loops resist any delamination. The tensile strength of the multiaxial warp knit composites increased by about 5–12% compared with the theoretical values computed from classical lamination theory. It is generally accepted that impact induced delamination area increases with the increase in the total absorbed impact energy in collisions with foreign objects. But the multiaxial warp knit composites showed that the total absorbed impact energy decreased with the increase in through-the-thickness reinforcement fibres. The multiaxial warp knit composites showed reduced vertical deformations compared with woven laminates, as the reinforcing loop density increased.