The purpose of this study is to investigate the strain rate dependence of design concept based on effective width theory for impact absorption member. In recent years, in order to achieve weight reduction, improvement of fuel efficiency and collision safety, high strength steel is adopted to make thin-walled members of automobile. When the member is subjected to crash impact, high strength steel is plastically deformed to absorb the impact energy. However, in case that elastic buckling is occurred before full cross-section of the member is yielded, there is a problem that expected impact absorption ability cannot be obtained even if material is high strength. While the von Karman's effective width theory have conventionally been applied to avoid occurring the elastic buckling in automotive design, the theory is developed based on sheet buckling mechanics under static compression. We investigate the influence of cross-sectional dimensions, material strength and crushing strain rate on buckling behavior using numerical analysis and drop-weight experiment. As a result, cross section of the member become effective against axial crush with increasing crush speed. It is found that the design based on the existing theory is provided enough evidence of safety, i.e., optimized design criteria can be proposed.
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