Deformation rate dependence on fracture characteristics of third generation Advanced High Strength Steel

The gradually more stringent environmental and safety regulations in the transport sector have made third generation Advanced High Strength Steel (3rd-gen AHSS) grades excellent alternatives to lower strength steel grades and have continuously been adopted by the automotive industry for body-in-white parts and energy absorbing safety components. Recently, essential work of fracture (EWF) has emerged as a viable material characterisation method to rationalise edge crack resistance and crashworthiness. However, much of the published data is still based on quasi-static conditions, which do not reflect the conditions during crash situations typically involving high deformation rates. This paper presents an experimental study on the deformation rate-dependence of fracture characteristics of three 3rd-gen AHSS grades. The results show that the fracture toughness, measured using the EWF method, increases significantly with the loading rate, although the differences in conventional tensile properties are modest. The increase is due to a combination of rate-dependent hardening combined with a much more ductile failure at a higher loading rate.