Study on damage mode and damage evolution of fibre metal laminates subjected to low-velocity impact

In order to improve fatigue property and impact resistance of aircraft structure, people design one new kind material called fibre metal laminates (FMLs) which consist of 2024-T3 aluminium alloy sheets bonded together with glass fiber prepreg. In order to study damage features of FMLs during impact, drop-weighted low velocity impact tests are performed and the results are compared with those of monolithic 2024-T3 sheets. Dynamic responses of FMLs are analyzed and damage modes are summarized according to damages at different impact energy. There are three inflection points in the curve of crack length and indentation depth versus impact energy: crack initiation, crack branching, and fully perforation. Finite element calculations are used to simulate the impact responses of FMLs to study the interaction between different layers. Damage evolution of delamination between aluminium and fibre layers is discussed, and the shape of delamination is almost elliptical with the major axis perpendicular to the rolling direction. Meanwhile, simulation results of force-time curves at 15J and 45J energy are compared with the experimental results and the differences of maximum force are 10.2% and 5.6%, respectively, which verifies that the finite element calculations can be used to study dynamic response of FMLs under low velocity impact.