An improved physically based behaviour law for ferritic steels and its application to crash modelling

An improved physically based behaviour law for ferritic steels is presented in this paper, and used to perform crash simulations. Flow stress depends on three contributions: the friction stress, the work hardening at low strain rate and the effective stress derived from the viscoplastic potential. These three terms are in most existing approaches simply summed up, but an original alternative mixing solution has been proposed for bcc metals by Edgar Rauch. The viscoplastic potential comes from the most general definition of a thermally activated mechanism at the dislocation gliding scale. The law intrinsically contains a threshold stress and exhibits only two unknown physical variables (activation volume and energy). The athermal quasi-static behaviour is finally described thanks to a linear combination of a Swift and a Hockett-Sherby laws. The complete model is then validated on the available data for two commercial ferritic steel. The predictions show a very good agreement with experimental data, and allow a good description of the temperature effects with a small numbers of parameters.