Thermo-micro-mechanical modeling of plasticity and damage in single-phase S700 steel

Abstract

In this study, a Thermo-micro-mechanical (TMM) model to describe the viscoplastic flow of polycrystalline metallic materials was extended by integration of micromechanical damage. The original TMM model [1] incorporated the fundamentals of dislocation motions during metal deformation, using microstructural state variables (MSVs) for the statistical quantification of dislocations, represented through the dislocation density. These MSVs track dislocation evolution throughout deformation, allowing for the material behavior and mechanical properties in cold and warm regimes (up to 500 °C) to be derived as functions of these state variables. A key advantage of the TMM model is its ability to transfer MSVs across multi-step process chain simulations, thereby accounting for the deformation history of materials in subsequent processes. However, the previous model was limited to the plastic regime and cannot be applied to processes involving damage and fracture. The primary objective of the current study is to extend the TMM model to predict fracture and damage. Therefore, the Gurson-Tveergard-Needleman (GTN) model, a widely recognized micromechanical damage model, was integrated into the TMM model to describe the material behavior comprising plasticity, damage and fracture (D-TMM model). This integration introduces void fraction from the damage model as an additional state variable alongside the existing MSVs, thus enabling the transfer of both deformation history and damage accumulation across the process chain. The constitutive equations from both models are numerically integrated, and their parameters are calibrated for a commonly used micro-alloyed high strength construction steel – S700. The model is subsequently tested under isothermal conditions up to 500 °C, non-isothermal conditions, and across a range of strain rates.