Energy-absorption mechanisms in Kevlar multiaxial warp-knit fabric composites under impact loading

The objectives of this study are to characterize the impact behavior and damage tolerance properties, on the basis of energy approach, of Kevlar multiaxial warp-knit fabric composites and woven and unidirectional composite laminates. The total impact energy is classified into four categories including delamination energy, membrane energy, bending energy and rebounding energy, and the contributions of each energy absorption mechanism have been evaluated. The membrane and bending energy were calculated from image analysis of the deformed shape of the impacted specimen while the delamination energy was calculated by using the deplying technique. The multiaxial warp-knit composite showed higher impact fracture toughness and bending properties and this resulted in a bending energy increase and reduced delamination while the membrane and delamination energy were the dominant energy-absorption modes for the woven composite laminate. The delaminated areas in the woven laminates were much larger than those in the multiaxial warp-knit composites, while the delamination energy absorption was slightly higher since the impact fracture toughness of the woven laminate was much smaller than those of the multiaxial warp-knit composites.