Micromechanical modeling of failure in dual phase steels

Abstract

Having brittle martensitic islands diffused in a ductile ferrite matrix, dual-phase (DP) steels are known for their high formability and favorable material properties. Although they have already proven their advantages in the industry, there are still discussions regarding their microstructure-macroscopic response link. In order to effectively exploit their advantages and analyze their ductility in metal forming operations, the failure mechanisms of DP steels must be well examined following a micromechanics-based approach. There are a number of failure mechanisms to be addressed at the micro scale such as ferrite-martensite and ferrite-ferrite interface decohesion as well as martensite cracking depending on the different microstructural parameters and stress state. A crystal plasticity based finite element framework for RVE calculations is followed here based on the previous work which focuses solely on the plastic deformation (see [1]). Isotropic J2 plasticity model is employed for the hard martensite phase while the rate-dependent crystal plasticity framework is used for the ductile ferrite phase. Cohesive zone elements are inserted at the ferrite-martensite and ferrite-ferrite interfaces for intergranular cracking analysis, besides, intragranular cracking in martensite phase is addressed through an uncoupled damage model. First, a preliminary study was performed in order to identify and calibrate aforementioned failure models, then, various 3D polycrystalline RVEs having different microstructural parameters loaded with different stress triaxialities are analyzed and discussed adding up to the preliminary discussions presented in [2].