Effect of in-lath slip strength on the strain partitioning in a dual-phase steel investigated by high-resolution digital image correlation and crystal plasticity simulations

Abstract

In this study, the effect of different modeling hypotheses for the plastic deformation of lath martensite was investigated through an integrated experimental–numerical approach. The local plastic strain distribution of a dual-phase steel with a coarse microstructure was quantified by high-resolution digital image correlation analysis. The same area was reproduced in a crystal plasticity finite element model using the electron backscatter diffraction measurement of the specimen surface prior deformation. Different modeling hypotheses in terms of in-lath and out-of-lath slip strength as well as boundary and bulk elements were explored. It was found that early plastic deformation in lath martensite grains predominantly took place at various interfaces in the form of slip bands parallel to the in-lath slip planes in blocks exhibiting high in-lath Schmid factor. A comparison between experiment and simulations suggested that assuming a lower strength and hardening rate for in-lath slip systems of boundary elements better reproduced the plastic strain fields in martensite grains. However, the different models showed limited effect on the strain distribution within ferrite grains and on the local stress–strain path at void nucleation sites. This suggested that the main factor affecting early strain concentration and subsequent damage initiation in ferrite grains was the phase morphology and strength contrast.