Advanced elastic-plastic constitutive models for medium-thickness high-strength steel plates: Microstructure-based parameter identification and verification

Replacing castings with medium-thickness, high-strength steel sheet (with thickness exceeding 3 mm) stampings can save raw materials and energy, and many medium-thickness plate parts are used in commercial vehicle frame assemblies and cab mounts. However, there are obvious differences between the sheet metal forming mechanisms of medium-thickness plate parts and thin sheet parts. There is a lack of systematic research on the issues of anisotropy, springback, non-uniform material flow, and fracture that exist in the sheet metal forming of medium-thickness plate parts. In this study, we coupled the three-dimensional anisotropic yield criteria Hill 48 and the kinematic hardening models (Armstrong-Frederick) to develop elastic-plastic constitutive models for the forming simulation of medium-thickness high-strength steel plates. Taking the 5-mm-thick 750L high-strength steel as the research object, for the problem that the anisotropic yield criterion parameters (especially in the thickness direction) are difficult to calibrate, we employed high-resolution full-field crystal plasticity simulations to obtain the parameters of the yield criterion, and determined the material parameters of the kinematic hardening models by the inverse analysis method. Through this multiscale modeling technique, we obtained the complete constitutive parameters of the material, which were verified by mechanical experiments with nonlinear strain paths. The effectiveness of different model combinations in predicting the plastic behavior and mechanical responses on medium-thickness high-strength steel plates is further evaluated.