| The superior combination of strength and ductility of advanced high strength steel (AHSS) alloys makes them particularly attractive for forming complex parts needed in the global automotive industries. In recent years, the production of AHSS sheet has been of interest for lightweight automotive applications without compromising either performance or cost standards. The federal government has been making unceasing demands from automotive companies to produce automobiles with fewer emissions in order to reduce pollution, and minimize petroleum consumption. Consequently, developing lightweight vehicles has become increasingly important for the automotive industry in recent years. New challenges in sheet metal forming processes emerged with the application of the new generation of AHSS, resulting in additional research efforts in experimental, theoretical, and constitutive modeling. Accordingly, the development and application of new constitutive equations and failure criteria for AHSS sheets also increased. It is particularly challenging to understand how the constituent phases in AHSS contribute to their higher strength, and resistance to localized necking and fracture. Also, volume fraction, grain morphology and distribution, and micromechanical properties of constituent phases contribute significantly in the selection of the material to be used for automotive applications. To overcome these challenges with the new generation of AHSS, the application of computer-aided material design or integrated computational materials engineering (ICME) with multiscale modeling of material processing is highly recommended.;In this study, a computationally efficient, rate independent, crystal plasticity finite element (CPFE) model was used to simulate a multiphase AHSS sheet undergoing a large plastic deformation. The CPFE model was developed and implemented into ABAQUS as a user material subroutine, VUMAT, to capture the mechanical properties of different phases of the steel sheet based on their individual plastic deformation and slip systems. The macroscopic behavior of the polycrystalline aggregate was then predicted based on the volume-averaged response of the representative phases, and their volume fractions in the steel sheet. The capability of the multiphase CPFE model was investigated based on experimental results obtained from a quenched and partitioned Q&P980 steel sheet. The results from the CPFE model were evaluated based on microscale uniaxial tension tests, and macroscale formability and stamping tests. In all of the CPFE simulations, a random texture distribution was assumed for each grain. However, to introduce the effect of inhomogeneity, two different methods were used to model the initial volume fraction distribution of each phase. Inhomogeneity of the sheet metal related to inhomogeneous distribution of phases and using a groove region in the specimen based on the Marciniak-Kuczynski (MK) theory was also considered for the calculation of the forming limit curve (FLC) using the CPFE model (MK-CPFE). The numerical study of the effect of mechanical properties of constituent phases on the FLC suggests that it is possible to design forming limit curves that would lead to textures that could enhance the resistance to localization. Furthermore, the accurate prediction of strains at the onset of necking of a stamped part suggests that a microstructure-sensitive model could be highly desirable for the stamping simulation of the multiphase, third-generation advanced high strength steel (3GAHSS). |
