Investigations concerning the strain rate behaviour of modern sheet steels for autobody applications

In a research project, which was commonly carried out by the steel and automotive industry, the determination of dynamic properties and thus a description of the material behaviour at high speed testing were performed. For this, 20 sheet steels have been investigated in dynamic tensile tests at different testing temperatures (40, 23 and 100degreesC) and different strain rates (1, 20, 250 and 500 s-1). Besides the starting materials, selected steels with a defined predeformation and heat treatment were tested. The results indicated that different steel groups exist which show a varying temperature and strain rate dependence. Low alloyed ferritic steels revealed a strongly reduced strain hardening potential at low temperatures and high strain rates. On the other hand multiphase steels did not show this behaviour. Still using this parameter combination, considerably higher strain hardening values could be obtained. These investigations showed how important reliable data for FEM-crash simulation seem to be. For this, it is essential to determine these data in the relevant temperature and strain rate range to avoid misinterpretations concerning the material behaviour on the basis of the data from the quasistatic tensile test.