PSI - Issue 68

Rintaro Tsuda et al. / Procedia Structural Integrity 68 (2025) 674–680 R. Tsuda et al. / Structural Integrity Procedia 00 (2025) 000–000

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7. Conclusions The following conclusions are obtained.

1, By using the secant method, we have developed a method of elasto-plastic FEM analysis that can reflect the changes of the volume fraction in the constitutive equation. This module enables accurate analysis because not only the amount of plastic strain but also stress triaxiality can be treated as elements affecting the volume fractions of the iinclusion phases. 2, In-situ neutron diffraction experiments during tensile deformation were conducted to obtain the single phase stress and the volume fraction of each phase. Based on the results, convergence calculations with the secant method were performed assuming the strain ratio, and the constitutive equation of the single-phase was obtained. 3, Simulation of tensile test of SUS316L at 20K and 173K were performed using the developed FEM module. The results are in good agreement with the experimental results. 4, Simulation of a three-point bending test was performed. Compared with the results of the method developed in this study, the results of the conventional elasto-plastic FEM show smaller values of the maximum principal stress at the crack tip. It is possible that the conventional method underestimates the stress at the crack tip, where the transformation is large, because it does not take into account the change in the constitutive equation due to SIMT. Acknowledgements This article is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO). The author expresses sincere thanks to PWH committee members and LH2 WG members for fruitful discussions. Also, the authors thank to Mr. Soraji from the University of Tokyo that often takes care of coding in FORTRAN for user subroutine, UMAT. References Beese, A. M., Mohr, D., “Effect of stress triaxiality and Lode angle on the kinetics of strain-induced austenite-to-martensite transformation”, Acta Materialia, Volume 59, Issue 7, 2011, Pages 2589-2600. Lebedev, A. A., Kosarchuk, V. V. “Influence of phase transformations on the mechanical properties of austenitic stainless steels”, International Journal of Plasticity, Volume 16, Issues 7–8, 2000, Pages 749-767. Matsumura, O., Sakuma, Y., Takechi, H., “Trip and its kinetic aspects in austempered 0.4C-1.5Si0.8Mn steel”, Scripta Metallurgica, Volume 21, Issue 10, 1987, Pages 1301-1306. Morohoshi, R. and Kawabata, T., “Effect of Stress Field on TRIP Behavior and Its Influence on Fracture Behavior of Commercial Stainless Steels at Cryogenic Temperature”, Proceedings of IIW2022 conference, Tokyo, 2022 Polatidis, E et al., “The effect of stress triaxiality on the phase transformation in transformation induced plasticity steels: Experimental investigation and modelling the transformation kinetics”, Materials Science and Engineering: A, Volume 800, 2021, 140321. Tsuchida, N., Tomota, Y., “A micromechanic modeling for transformation induced plasticity in steels”, Materials Science and Engineering: A, Volume 285, Issues 1–2, 2000, Pages 346-352. Tsuchida, N., Ishimaru, E., Kawa, M., “Role of Deformation-Induced Martensite in TRIP Effect of Metastable Austenitic Steels”, ISIJ International, 2021, Volume 61, Issue 2, Pages 556-563. Tsuchida, N., Ueji, R., Inoue, T., “Effect of Temperature on Stress–Strain Curve in SUS316L Metastable Austenitic Stainless Steel Studied by In Situ Neutron Diffraction Experiments”, ISIJ International, 2021, Volume 61, Issue 2, Pages 632-640. Weng, G. J., “The overall elastoplastic stress-strain relations of dual-phase metals, Journal of the Mechanics and Physics of Solids 38 (1990) 419.