Three-Point Bending Crash Performance of Advanced High Strength Steels

Drop tower crash tests in a three-point bending configuration were carried out on spot welded box sections, adhesive bonded box sections, and laser welded cylindrical tubes made from a variety of advanced high strength steels. In the tests, a 147-kg indenter with a 28-cm diameter impacts the specimen at approximately 6 m/s, and the bending loads and energy absorption are determined. The results show that the maximum bending loads best correlate to the product of yield strength and thickness-squared, while the energy absorbed over 10-cm displacement best correlates to ultimate tensile strength times thickness-squared. As such, higher strength steels can be used to improve crash performance without increasing weight or to maintain crash performance with weight reduction. Other significant findings of the study are as follows. Bake hardening alone may improve bending crash performance slightly, while cold rolling and baking does not. Compared to the box section geometry, the cylindrical tubes have similar maximum bending loads and higher energy absorption at 10-cm displacement. Finally, purely adhesive bonding appears to be better suited for hot-dip galvanize (GI) than for hot-dip galvanneal (GA) coated sheet steels.