The effects of cross sectional shape of polygonal shell members and material properties on impact deformation behavior of ultra high strength steel members were studied by dynamical impact tests and numerical analysis. The result of dynamical impact tests have shown that the buckling behavior is influenced by the width of plane regions and material properties. The buckling load increases as the ratio of the width of plane regions to sheet thickness (Wp/t) decrease, which is well correlated with the flow stress of 7% strain of the material. On the other hand, decrease in the Wp/t makes ultra high strength steel members more susceptible to fracture resulting in reduction in the buckling load. FEM calculations show that reduction in the Wp/t leads to increase in principal strain at ridgelines on the top of buckling wrinkle, which is a major site of initiation and propagation of fracture. With the materials having good uniform or local elongation, the fracture on impact can be suppressed.
