Realistic morphology-based Representative Volume Elements for dual-phase steels

Abstract

We present a framework for the digitization of Dual-Phase (DP) steel microstructures into three-dimensional Representative Volume Elements (RVEs). Using a stack of microscopy images 6-μm high, separated by approximately 0.3 μm, in a microstructure analysis software, we obtain solid models, and subsequently finite element meshes of RVEs for three DP steels with distinct microstructures. No approximations with regards to the shape, size, and distribution of the second phase particles are required. A comprehensive mean-field model due to (Allain et al., 2015) obtains flow curves for the martensite and ferrite; ferrite grain size, average martensite island size, and steel composition are the inputs. It bears emphasis that no additional parameter adjustments to the flow curves was required. The finite element model was solved with an implicit integration scheme to obtain uni-axial stress–strain curves that agree with the experimental curves to within 8%. We use our framework to propose some guidelines for the development of RVEs. We also show that the plastic strain between the martensite islands, at the onset of necking, is approximately 2.5-3 times the global necking strain. Furthermore, we make a case for the iso-work assumption made in one-dimensional mean-field models that treat DP steel as a two phase composite.