Force attenuation of aluminum foam core and stainless honeycomb armored sandwich specimens subject to dynamic loading

Porous sandwich core specimens are finding increased use in impact limiting applications such as armor protection due to their ability to attenuate transmitted forces via energy dissipative core crushing. For this research, dynamic testing was performed using a Hopkinson bar and gas gun and the transmitted force response of aluminum foam and stainless steel honeycomb sandwich specimens were captured at various stages of core crush. The initial contact force did not change significantly with velocity, but instead, remained relatively constant for a given core density. Increasing core density did increase initial contact force (stiffer response), but also lowered peak force recorded at core densification due to the amount of energy that could be dissipated through the sandwich specimen. Examining two representative coupon specimens (one 0.5 g/cc aluminum foam core and one 6.35 mm cell-size stainless steel honeycomb core), finite element analysis based on an isotropic foam material model in Abaqus/Explicit was able to simulate the transmitted force time histories and appeared similar to the actual dynamic force data. The same material model when applied to a larger 610 × 610 mm panel and subject to a wide area dynamic load experienced similar stress concentrations and response as actual panel tests. The implication of this investigation is that the force attenuation and dynamic behavior of small coupon specimens can be used to validate and predict the behavior of larger panels under dynamic loading.