Effect of Strain Rate on Impact Behavior of Aluminum Foam

Due to increase of terrorist threats and attacks, reasonable and economical designs for impact resistant protective structures are necessary. To ensure the appropriate use of aluminum foam panels as sacrificial panels, the compressive behavior of aluminum foam must be investigated. This work presents broad experimental and numerical investigations of the strain rate sensitivity of closed-cell aluminum foam and its effect on the strength parameters of foam. Air gun tests for direct impact testing and split Hopkinson pressure bar (SHPB) tests were performed to investigate the deformation and energy absorption characteristics of aluminum foam with an increase in strain rate. Along with these experiments, numerical finite element analyses for both air gun and SHPB tests were performed with LS-DYNA. For the explicit analysis, the strain rate was considered in the material model, and the experimental work was verified by the numerical approach. The deformations and yield strengths of the aluminum foam were investigated with increasing strain rate. Parametric analyses were also conducted to determine the minimum required thickness of aluminum foam and an equation is proposed to calculate the minimum foam thickness while considering the effect of the strain rate. Moreover, to ensure realistic and economical designs for protective structures, a recommendation was provided for the aluminum foam thickness. This concept is compared with another study where strain rate effect was not considered for a close range blast load resistant protective structure. The pressure transmitted through the aluminum foam to the attached concrete wall was measured and the magnitude of reflected and mitigated transmitted pressure was observed. Consideration of strain rate effect leads to a lower required foam thickness and a lower magnitude of the pressure transmitted to the structure.