The ballistic impact behavior of composites reinforced by biaxial weft knitted UHMWPE fabrics

Ultra-high Molecular Weight Polyethylene (UHMWPE) fiber is a kind of high-tech fiber proved to be the best bulletproof fiber by far. Because of a good ability of deformation Biaxial Weft Knitted (BWK) fabrics is a possible candidate for some molded bulletproof products such as helmets. The ballistic impact Behavior of Biaxial Weft Knitted UHMWPE composites has been investigated in this paper. It was found that ballistic performances were influenced by the pressing pressure strongly. The composites were manufactured under pressure of 1Mpa, 2Mpa, 5Mpa, respectively, which results in different matrix contents and ballistic performance. Those samples with higher matrix contents were penetrated by the '51' lead-core bullet fired by the '54' handgun, whereas a sample with lower matrix content arrested the bullet effectively. The ballistic impact responses of penetrated and non-penetrated composites were analyzed comparatively. Both in penetrated and non-penetrated composites, the main failure mode of fiber is cut-out by shear, especially for the penetrated samples, in which there seem to exist a change of failure modes from shear fracture to tensile rupture along the thickness of the target. But for the non-penetrated composites, tensile rupture can be observed only in those layers where the bullets were stopped. Most fibers in the following layers behave in an elastic manner although a 'back bulge' would come into being under ballistic impact. The difference of the delamination in the tow kinds of samples were studied also. Because of the peculiar fabric construction, some special phenomena were observed in the research such as yarn slippage and the fragments of the bonding coils.