Compressive strain rate dependence and constitutive modeling of closed-cell aluminum foams with various relative densities

The dynamic compressive behavior of closed-cell aluminum foams with different relative densities at a wide range of strain rates up to 4000 s−1 was investigated using a 37-mm Split Hopkinson Pressure Bar (SHPB) apparatus. The 30-mm-diameter specimens with two thicknesses (i.e., 6 and 10 mm) and three nominal relative densities (i.e., 0.11, 0.16, and 0.21) were fabricated. The influences of strain rate, relative density, specimen thickness on the mechanical properties of aluminum foams (e.g., stress–strain relationship, collapse stress, plateau stress, densification strain, and energy absorption) were examined. The results indicate that the collapse stress, plateau stress, and densification strain of the aluminum foams with three relative densities exhibit obvious strain rate sensitivity. The collapse stress and plateau stress have a stronger density sensitivity and relatively weaker strain rate sensitivity. The specimen thickness has a very slight influence on the specimen strength at a lower strain rate (600 s−1), but this leads to a greater influence at a higher strain rate (2000 s−1). The energy absorption capacity of the closed-cell aluminum foams increases with increased relative density and strain rate in both quasi-static and dynamic compression. Finally, a multiparameter nonlinear elasto-plastic constitutive model was proposed to describe the typical three-stage features of stress–strain response in aluminum foams. There was acceptable agreement between theoretical predictions and experimental results.