Full-Field Quantitative Determination of Strain and Stress Partitioning in Medium Mn TRIP Steels

The aim of this paper is to present a new method for the quantitative determination of strain and stress partitioning in medium Mn transformation-induced plasticity (TRIP) steels with typical ferrite–austenite dual-phase microstructures. Firstly, based on scanning electron microscope (SEM) imaging, the strain field of the specimen surface during tensile deformation can be obtained using a developed microscopic digital image correlation (DIC) method. The different phases involving ferrite, austenite and nascent martensite after transformation are recognizable from the strain field, then the strain partitioning between phases can be solved experimentally. Secondly, regarding the stress partitioning, the constitutive models of the phases involved are established, and the relevant model parameters are identified using a proper regression method under the premise of the law of mixture and the iso-work law. Finally, strain and stress can be computed simultaneously at the phase level. The results show that there is significant inhomogeneity in the distribution of strain in different phases, as well as the distribution of stress. The proposed method allows providing valuable information for assessing the weight of different phases in contributing to the macroscopic mechanical properties of multi-phase steels, such as strength and ductility. This method can also be used to simulate the mechanical response of medium Mn TRIP steels at different austenite stabilities and different initial volume fractions of austenite, indicating therefore a great potential for improving material properties via microstructural tuning. Graphical Abstract Full-field quantitative determination of strain and stress partitioning in medium Mn TRIP steels.