FEM Module Development Considering TRIP

Martensitic transformation in metastable austenitic stainless steel is known to be the stress field dependent. The purpose of this study is to consider this stress-field dependence of the transformation in elasto-plastic finite element analysis and to make the analysis more accurate. The single-phase stress and volume fractions of each phase were determined by in situ neutron diffraction experiments. Tensile tests were conducted at 20 K and 173 K, respectively. Using the experiment data and assuming the strain ratio of each phase, iterative calculations were performed to determine the single-phase stress-strain relationship. Elasto-plastic FEM analysis method is developed that can obtain the constitutive equation of the composite phase from the single phase stress-strain relationship, depending on the change in the volume fraction of each phase. In this study, the secant method by Weng is used to derive the stress-strain relationship of a two-phase steel from the stress-strain relationship of each phase. The simulation of a tensile test of SUS316L at 20 K using this method was in good agreement with the experimental results. Simulation of fracture toughness tests was also conducted. By comparing the results with those obtained by the conventional method, the influence of the stress-field-dependent martensitic transformation at the crack tip is discussed.