Localized deformation in aluminium foam during middle speed Hopkinson bar impact tests

Split Hopkinson pressure bar (SHPB) technique is a widely adopted method to study the dynamic mechanical behaviors of materials. However, the strong localization of the deformation in aluminium foams (near the ends of the specimen) may invalidate the assumption of uniform strain within the specimen granted in the analysis of SHPB results. To appraise how critical this issue could be, the deformation process of aluminium foam under middle speed impact was investigated by combining SHPB technique with high speed photography. Based on the experimental results, finite element analysis was carried out to explore the characteristics of the localized deformation in aluminium foam. The strain distribution was quantitatively analyzed and showed the dependence on the imposed strain rate. An evaluation of the deformation localization by defining maximum loacalized strain and strain rate indicates that the maximum strain and strain rate in the specimen can be more than 100% higher than the average values.