The experimental and numerical study of AA6061-T6 aluminum alloy under repeated impacts

In this study, we aimed to investigate the effect of repeated impact loading on the fatigue and failure behaviors of AA6061-T6. An improved drop hammer impact testing machine was utilized for the experimental tests of Unotched three-point bending specimens under different impact energies. Based on the microscopic fracture features, we selected the Gurson-Tvergaard-Needleman (GTN) model as the damage model for AA6061. Then, we established a numerical implementation of impact damage accumulation-based FEM simulation. By calibrating the parameters of the GTN model, we were able to achieve the impact progressions of U-notched three-point bending specimens under repeated impacts. The testing results indicate that the impact fatigue life decreases exponentially with increasing impact energy. As the repeated impact energy increases, the fracture surfaces transition from visible fatigue striations to abundant ductile microvoids. Comparison between the experimental tests and the numerical simulations of the U-notched three-point bending specimens reveals a high degree of consistency in terms of life and crack propagation for the repeated impacts with high impact energy. This demonstrates the good applicability of the GTN model in capturing the repeated impact behavior of AA6061 under high impact energy. Furthermore, the simulations indicate that the specimen's notch experiences tension, compression, and reverse yield processes due to the rebound of the specimen in a single impact. This leads to a slight reduction in the void volume fraction during repeated impacts.