Numerical Simulation of Plastic Softening at Elevated Temperatures Using Gradient Damage Methodology S. Baruah∗, I. V. Singh Department of Mechanical and Industrial Engineering, Indian Institute of Technology, Roorkee, Uttarakhand, India ∗ s_baruah@me.iitr.ac.in, Keywords: Plasticity; Gradient Damage; Elevated Temperatures In the present work, gradient plasticity-based damage methodology has been employed to capture the plastic softening behaviour under monotonic loading at elevated temperatures. The conventional approach to capture the stress-strain curve of materials using classical plasticity-based simulation often suffers from its incapability to accurately capture the softening curve. This drawback becomes more pronounced at elevated temperatures where an early onset of softening occurs. Therefore, the present work investigates the stress-strain softening behaviour of steels under tensile load at high temperatures using gradient based elasto-plastic damage methodology. The framework originally developed by [1] has been modified by using a temperature-dependent damage parameter. Furthermore, a damage variable is incorporated in the yield function of the classical plasticity model. The damage accumulation occurs through a non-local strain variable. The process of gradual reduction of stiffness with increasing load captures the softening behaviour of the material. Two example problems are numerically investigated, firstly a S900 steel specimen and secondly a Q960 steel specimen. From experimental evidences in [2], [3], it is found that the present methodology satisfactorily captures the plastic strain behaviour upto 600◦C for S900 steels and upto 500◦C for Q960 steels. The results are also compared with classical von-Mises plasticity model with Ramberg-Osgood behaviour, and it is observed that the present methodology provides a better agreement with the experimental data. References [1] Engelen, R. A., Geers, M. G., Baaijens, F. P. (2003). Nonlocal implicit gradient-enhanced elasto-plasticity for the modelling of softening behaviour. International journal of Plasticity, 19(4), 403-433. [2] Narimani, M., Hajjari, E., Eskandari, M., Szpunar, J. A. (2023). Elevated temperature tensile behavior of S900 HSLA steel and its welded joints. Journal of Constructional Steel Research, 203, Article no. 107782. [3] Wang, W., Zhang, Y., Xu, L., & Li, X. (2020). Mechanical properties of high-strength Q960 steel at elevated temperature. Fire Safety Journal, 114, Article no. 103010. 72
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