The forming limit curve for multiphase advanced high strength steels based on crystal plasticity finite element modeling

Abstract

A computationally efficient rate independent crystal plasticity finite element (CPFE) model was used to predict the forming limit curve (FLC) for a multiphase advanced high strength steel (AHSS). The CPFE model accounts for mechanical properties of the steel phases based on their individual plastic deformation and slip systems. The macroscopic behavior of the polycrystalline aggregate was predicted based on the volume-averaged response of the representative phases, and their volume fraction in the steel sheet. In addition to the random texture distribution assumption for each grain, the volume fractions of various phases were also assumed to be randomly distributed at each integration point. The microstructural inhomogeneity of the material, as well as a geometrical inhomogeneity in the form of a groove region in the specimen, based on the Marciniak-Kuczynski (MK) theory, were considered in the calculation of the FLC using the CPFE model (MK-CPFE). The validity of predicted FLC for quenched and partitioned QP980 steel was confirmed by comparing the results with experimental measurements. The FLC calculated by CPFE model showed that the presence of microstructural inhomogeneity allows for a more realistic prediction of the localized necking phenomenon. Subsequently, the FLC was used to compute the limit strains for the T-shape part stamping process. The limit strains and the punch force-stroke relationship for the T-shape part predicted by the multiphase CPFE model were in good agreement with experimental results.