Bio-Inspired Cross-Spiral Carbon Fiber Composites: Impact Resistance and Damage Tolerance Under Multiple Low-Velocity Impact.

This study investigates the impact resistance and damage tolerance of bio-inspired cross-spiral (CS) laminates under multiple low-velocity impacts. Two impact conditions were considered: repeated impacts at the same location and double impacts at different locations. Low-velocity impact tests, ultrasonic C-scan inspection, and compression-after-impact (CAI) tests were conducted to evaluate the impact response, internal damage, and residual compressive strength. The results show that repeated impacts at the same location intensified deformation and damage accumulation. When the number of impacts increased from 1 to 15, the peak force and maximum central displacement increased by 20.26% and 26.21%, respectively, while the absorbed energy decreased by 70.96% and the damage area increased by 113.67%. The variations in response parameters and damage area became less pronounced as the number of impacts increased. Under double impacts at different locations, increasing the impact spacing reduced damage coupling between the two impacts. When the spacing increased from 0 mm to 80 mm, the CAI strength increased by 11.02%. Overall, repeated impacts at the same location reduced the residual compressive load-bearing capacity, whereas larger impact spacing helped improve the CAI performance.