Experimental investigation on the strain-rate effect and inertia effect of closed-cell aluminum foam subjected to dynamic loading

In this paper, a series of experiments were conducted to clarify the effects of the strain rate and inertia on the deformation behavior of closed-cell aluminum foams under impact. The quartz-crystal technique was employed to analyze the stress uniformity of aluminum foam samples under split Hopkinson pressure bar (SHPB) loading. It was revealed that the condition of stress uniformity is hard to reach for a thicker foam sample, and the strength of aluminum foam is sensitive to strain rate. Two different direct-impact Hopkinson pressure bar (DHPB) methods were introduced to validate the three deformation modes, i.e. homogeneous mode, transitional mode and shock mode. Results displayed that the stress at the front surface increased dramatically than that at the back surface as the impact speeds increased from 16 m/s to 113 m/s. The axial-inertia effect became more important than the strain rate effect under high speed impact. The dynamic deformation processes were recorded by a Phantom-675 camera and were analyzed through the digital imaging correlation (DIC) method. The deformation of aluminum foam in homogeneous mode was presented by the evolution of global distributed failure, but it was dominated by the local failure in shock mode.