Deformation failure mechanism and constitutive model of gradient aluminum foam under impact loading

The dynamic mechanical response and energy absorption characteristics of gradient aluminum foam under impact loading with strain rates of 150 s-1, 340 s-1, and 550 s-1 have been studied based on the Split Hopkinson Pressure Bar (SHPB) test in this paper. X-CT and numerical simulations were carried out to analyze the deformation of the micro-porous structure of gradient aluminum foam during impact compression. A constitutive model for gradient aluminum foam under impact load was further established. The results show that the mechanical properties of aluminum foam are positively correlated with the strain rate. The better energy absorption effect of gradient aluminum foams than the homogeneous aluminum foam under impact loading was confirmed. Negative gradient aluminum foam exhibited a 46.9 % higher specific energy absorption rate than homogeneous aluminum foam. The failure mode of homogeneous and positive gradient aluminum foam was observed to be 'from the proximal to the distal', whereas negative gradient aluminum foam exhibited a 'from the distal to the proximal' failure mode. The Sherwood-Frost model, considering the shape, density, and strain rate function correction, could accurately predict the impact stress-strain curve of gradient aluminum foam, which can be served as a reference for the optimal design of gradient aluminum foams.