Revealing bird-strike damage mechanisms for CFRP laminates through a novel sub-element level experiment and simulation

Slicing-loading impacts on fan blades, which often occur when birds are ingested into aircraft engines, have been extensively investigated because of their complex loading characteristics. The development of a sub-element level test method is critically needed to simplify the study of impact resistance in fan blades in response to bird strikes and to comprehensively understand the associated damage behavior in composite materials. In this study, a sub-element level test method is proposed to replicate the slicing-loading and surface-traveling impact characteristics of bird strikes, and the impact behavior of carbon fiber–reinforced polymer (CFRP) laminates across a range of velocities is systematically investigated using experimental and numerical approaches. The developed numerical model was validated to ensure that it accurately predicts and captures multiple deformation and damage modes during the impact event. The results reveal three distinct deformation modes of the laminate under bird strike, which lead to different damage modes. The deformation modes of the dominant damage behavior undergo a transition from single to combined effect with the increasing velocity. Analysis of the energy dissipation indicates a shift from predominantly intralaminar damage to a combination of intralaminar and interlaminar damage as the impact velocity increases. Two velocity thresholds were identified based on the correlation between delamination area and impact velocity, and these thresholds provide dual benchmarks for comprehensively evaluating the impact resistance of CFRP laminates. The findings of this study are expected to aid in the design of composite laminates for improved resistance to bird-strike impacts in aircraft applications.