Microstructurally-based multi-phase finite element analysis of bending in Advanced High Strength Steels (AHSS)

Understanding the bendability of Advanced High Strength Steels (AHSS) is critical for both the forming of components and improving crash worthiness. This paper addresses this for a Dual-Phase DP-980 steel. In tandem with experimental work presented elsewhere we have developed a Finite Element Analysis (FEA) to model both the 90° VDA V-Bend test and a simple 3-point bend test. The FEA utilizes HyperWorks and LS-DYNA as the simulation platforms. Multi-scale, multi-phase modeling is implemented, incorporating real microstructures to capture the stress and strain evolution of DP-980 steel throughout the respective bending procedures. In this framework, macro-scale models inform and drive micro-scale models, ensuring realistic strain localization. We have demonstrated that the strain histories for these two modes of bending are quite different, although the final strains are similar. We have used the model to demonstrate how altering the microstructure through modification of the Martensite Volume Fraction and the Carbon content, affects strain localization within both Ferrite and Martensite. Furthermore, varying the relative strengths of each microstructural phase has a large effect on phase strain partitioning which is known to be important to damage tolerance. The results help to establish a robust methodology for multi-scale bending simulations of multi-phase materials.