Comparison of damage in FMLs, aluminium and composite panels subjected to low-velocity impact

In order to improve the damage tolerance and anti-impact properties of aircraft structures, fiber metal laminates (FMLs) developed in Europe are successfully applied in commercial aircraft structures. In this paper, drop-weight low-velocity impact tests are performed on FMLs which consist of 2024-T3 aluminium alloy sheets bonded together by glass fiber prepreg. For comparison purposes, similar tests are conducted on monolithic 2024-T3 sheets and F300 quasi-isotropic composite panels. The penetration energy of the FMLs shows respectively about 40% and 6 times higher than that of the 2024-T3 sheets and composite panels; and the back side crack length of the FMLs is 30%-50% shorter than that in the 2024-T3 sheets at the same level of impact energy. Finite element models are developed to simulate the impact response of the FMLs. Ductile and Hashin damage initiation criteria are used to simulate the aluminium and fiber failure mechanisms respectively. The dynamic response of the laminates is analyzed and the damage mode is summarized. The simulation results agree well with the experimental findings.