Ballistic performance of CFRP under normal and oblique impacts by square fragments: Experimental, numerical, and theoretical investigations

High-performance carbon fibre-reinforced polymer (CFRP) composites are commonly used as external protective structures in military and aerospace applications and are frequently subjected to impact from fragments or projectiles. This study investigated the damage mechanisms of CFRP laminates under normal and oblique impacts from square fragments. Impact tests were conducted on 3–9 mm CFRP laminates using 4 g and 7 g square fragments at velocities ranging from 100 to 1300 m/s and impact angles from 0° to 60° Finite element simulations based on yarn-scale models were also performed. The results revealed that under oblique penetration conditions, the fragment edge initially contacting the target plate caused deeper shear damage. An analytical model was developed to predict the residual velocity of the fragments and the ballistic limit velocity (BLV) of the CFRP laminates. The average error between the model predictions and experimental results was 8.42 %, whereas that between the predictions and simulation results was 3.69 %. Interestingly, the analysis revealed a non-zero minimum resistance angle for the laminate under square fragment impact, at which the BLV of the target plate was minimised. The predicted distribution range of the minimum resistance angle in this study was 23–28° The developed predictive model and identified "minimum resistance angle" provide theoretical foundations for protective engineering design, bridging laboratory research to real-world high-risk applications such as military and aerospace.