Dynamic Response Mechanism and Cumulative Damage Effect of Al0.3CoCrFeNi High Entropy Alloy under Repeated Impact Loading

High entropy alloy (HEA) has become an important material for impact load response due to its excellent mechanical properties and energy absorption capacity. In this paper, the dynamic response behavior of Al0.3CoCrFeNi HEA plate under single and secondary impact loads was systematically discussed by molecular dynamics simulation, and the evolution of phase structure, dislocation distribution, energy absorption and cumulative effect of multiple impacts were revealed. The results show that under the first impact, the phase structure evolution and energy absorption mode of the plastic region of HEA plate exhibits significant velocity dependence. Under low velocity impact, energy is mainly absorbed by dislocation network; at medium velocity impact, both dislocations and disordered atoms contribute; under high velocity impact, disordered atoms dominate energy absorption. The length of dislocation lines follows a linear evolution equation of l=3162.8v1-1239.9 within the range of 0.5-0.8 km/s, while at higher velocities, dislocation line length decreases due to thickness limitations of the plate. Stress distribution analysis shows that the maximum stress has a quadratic relationship with velocity: σ1=-14.48v1+114.04v12+29.02, while the relationship between the boundary stress and the velocity in the plastic zone is σ2=2.81v1-0.42v12+9.44. In the context of the second impact, the geometric characteristics indicate that the HEA plate forms a trapezoidal damage region, with a relationship between the radius of the upper pit to the impact velocity expressed as r=3.29v1-0.45v12+2.67. Consequently, the minimum affected area from the second impact can be represented as L=-0.45(v12+v22)+3.29(v1+v2)+2×h×cot(θ)+5.34. In terms of impact resistance, an increase in the initial impact velocity leads to a greater residual velocity after the second impact, indicating a reduction in the resistance. At a distance of 10 nm from the impact center, the relationship between the ballistic limit and the first impact is vbl=-8.6ev1/769+1383.6. However, an increase in the second impact velocity gradually diminishes the effects of the first impact. This study provides a theoretical foundation for the optimization of target plate designs under multiple impact conditions.