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 da mage tolerance properties, on the basis of energy approach, of Kevlar multi axial warp-knit fabric composites and woven and unidirectional composite la minates. The total impact energy is classified into four categories includi ng delamination energy, membrane energy, bending energy and rebounding ener gy, and the contributions of each energy absorption mechanism have been eva luated. The membrane and bending energy were calculated from image analysis of the deformed shape of the impacted specimen while the delamination ener gy was calculated by using the deplying technique. The multiaxial warp-knit composite showed higher impact fracture toughness and bending properties a nd this resulted in a bending energy increase and reduced delamination whil e 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 composite s, while the delamination energy absorption was slightly higher since the i mpact fracture toughness of the woven laminate was much smaller than those of the multiaxial warp-knit composites. (C) 2000 Elsevier Science Ltd. All rights reserved.