Identification of mechanical responses of steel sheets under non-proportional loadings using dislocation-density based crystal plasticity model

A crystal-plasticity approach based on three-component dislocation density model is proposed, as a virtual experimental model, to accurately predict non-proportional anisotropic hardening behavior of ultra-thin sheet metals, a potential candidate for PEMFC (proton-exchange membrane fuel cell) bipolar plate. The model introduces three different populations of dislocations named forward, reverse and latent, which are selectively activated depending on load path changes. To validate the predictive capability as a tool for the virtual experiment, the model is validated by predicting flow behaviors of 1.2 mm thick extra-deep drawing quality steel sheet under compression- tension and two-step tension test. The model is then applied to the 0.1 mm thick ultra-thin ferritic stainless steel sheet. The model parameters are identified by the two-step tension test. The proposed model with the identified parameters can predict the tension-compression stress-strain curves, which are difficult to measure experimentally due to premature buckling for such thin sheet metals. The potential application of the crystal plasticity based virtual modeling to the springback prediction in the thin sheet metal parts is discussed in this study.