Quantification of damage evolution in stainless steel 316L based on 3D ex-situ X-ray CT and micro-damage model

Quantifying damage to improve the constitutive models that better account for damage prediction is of great importance in metal forming process. In this study, high-resolution micro-focus X-ray Computed tomography (CT) system, together with loading-unloading tensile test, were employed to quantify the 3D interactions of micro-voids evolution in the biocompatible alloy stainless steel 316L (SS316L). The specimen material was tensile deformed and interrupted at several strain intervals prior to failure, X-ray CT was then performed to quantify the damage evolution via the detected changing in size, number, distribution, and volume fraction of micro-voids (VFMV) after each specified strain increment. Thereby the nature of ductile damage, which involved the dynamic evolution mechanism of the nucleation, growth and coalescence of micro-voids, was revealed. Furthermore, an improved micromechanics-based damage (micro-damage) model considering large deformation condition was implemented into finite element (FE) package ABAQUS for the damage prediction. The damage of the specimen under tensile deformation with a wide range of stress states was predicted and a good agreement with experimental data was achieved in terms of damage distribution and evolution. It is concluded that the findings of this study not only reveal the dynamic evolution mechanism of the micro-voids in the damage process intuitively from the experimental point of view, but also provide more accurate material parameters for the theoretical damage modelling, so as to obtain more convincible damage prediction results in the metal forming process.