Damage Evolution of Cross-Ply Flax Fiber Reinforced Epoxy Composites Subjected to Repeated Impacts

The evolution of flax/epoxy composite laminate damage under low-velocity impact loading is studied. The plates were elaborated with a vacuum infusion manufacturing process to investigate how damages evolve with the number of impacts and energy level. The experimental apparatus used for multi-impact testing is an in-house-built impact fatigue machine, based essentially on the principle of crank-connecting rod mechanism, with a circular clamping fixture system for the specimens. The flax/epoxy laminates are composed of 12 plies with [0/90]3S stacking sequence. The low-velocity impact fatigue tests are performed at three energy ranges: 5 J, 6 J, and 7 J, and at different impact numbers for each energy level. The ranges of many impacts are chosen from the knowledge of failure impact number determined at the state of perforation. Indeed, initial tests are performed to determine the number of impacts to failure corresponding to full perforation of specimens. This study considers many impacts and low-impact energy to understand the damage development of the studied materials by observing impacted face and rear face cracks. We found that damage increases with the impact energy and the number of impacts. We also detect the presence of delamination by measuring crater depth and bump height.