Effect of material properties of advanced high strength steels on bending crash performance of hat-shaped structure

Systematic dynamic and quasi-static bending crash tests were conducted with high strength steels using a hat-shaped structure in order to investigate the effect of material properties on crash performance. Materials with a wide range of tensile strengths from 270 MPa to 1470 MPa and various microstructures such as interstitial free (IF), dual-phase (DP) and transformation induced plasticity (TRIP) steels were examined. Hat-shaped structures were prepared by two different processes (bending and draw-bending processes) to investigate the influence of strain-hardening on crash performance. The experimental results clarified the effects of sheet thickness, material strength and strain-hardening on crash characteristics. The effects of bending crash conditions, including crash speed and bending span, were also studied to understand how these factors influence crash behaviors. The sequence of the dynamic bending crash was investigated to elucidate the mechanism of crash performance. As a quantitative index of crashworthiness, the bending moment Mb was calculated from the mean force and bending span. The effects of both yield strength and sheet thickness on bending moment were investigated. Based on the experimental results, a simple method for estimation of bending crash performance using material strength and thickness as parameters was proposed in order to understand the relationship between the weight reduction effect and improvement of crashworthiness in automotive parts when using advanced high strength steels.