Failure behavior of 2A12 aluminum alloy plates subjected to hailstone impact

With the increasing deployment of high-altitude and high-speed aircraft, hailstone impacts pose a significant threat to the safety and integrity of aircraft structures. In this work, hailstone impact experiments and numerical simulations are performed to investigate the failure behavior and underlying mechanism of 2A12 aluminum alloy target plates. The Johnson-Cook (J-C) constitutive model for both 2A12 aluminum alloy and ice, and a stress-state dependent J-C failure model for the alloy are first determined by material tests. A coupled Finite Element Method-Smoothed Particle Hydrodynamics (FEM-SPH) framework is established to capture the fragmentation of the hailstone and the complex fracture process of the target plate. Test results show that the failure mode of the plate changes from a single dominant crack at an impact velocity of 220 m/s to petal-shaped multi-crack evolution at 240 m/s. The FEM-SPH simulations successfully reproduce the fragmentation of the hailstone, as well as the deformation process and crack patterns of the plates. Quantitative analyses along crack paths show that the elevation of both peak strain rate and local stress triaxiality at a higher impact velocity results in lower critical failure strain, which is the primary driver for the formation of multiple secondary cracks.