Computer Methods in Materials Science
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ISSN 2720-4081
e-ISSN: 2720-3948
Issue Date
2025
Volume
Vol. 25
Number
No. 3
Description
Journal Volume
Computer Methods in Materials Science
Vol. 25 (2025)
Projects
Pages
Articles
Polycrystalline plasticity analysis of cyclic loading and stress relaxation in 316H austenitic stainless steel
(Wydawnictwa AGH, 2025) Acar, Sadik Sefa; Yalçinkaya, Tuncay
The mechanical behavior of 316H austenitic stainless steel is investigated in this study under cyclic strain-controlled loading with and without hold periods at elevated temperatures. Understanding the low-cycle fatigue (LCF) and fatigue-creep interaction (FCI) characteristics is essential for ensuring the structural performance and safety of reactor components, particularly under conditions typical of modular and generation IV reactors. The new generation of nuclear power plants require more resistant and durable materials as the operating environments impose significantly higher demands, including increased neutron irradiation levels and elevated operating temperatures, leading to accelerated material degradation. A combined isotropic-kinematic hardening model within a crystal plasticity framework is employed to capture the cyclic and time-dependent mechanical response of the material. Model parameters are calibrated by fitting cyclic loading simulation results to experimental data at 550°C using polycrystalline representative volume elements (RVE). Strain-controlled uniaxial loading simulations are performed to analyze peak stress evolution throughout cyclic loading and stress relaxation behavior during strain-hold periods. The RVE simulation results are in strong agreement with experiments under LCF loading. For the loading with strain-holds, stress relaxation during hold periods exhibits two distinct stages: an initial rapid decay followed by a steady decline, both of which are captured in simulations. Beyond the macroscopic response, analyses reveal the heterogeneous evolution of field variables at the microstructural level, as strain hardening during loading and stress relaxation during hold periods varied across grains due to their crystal orientations and interactions with neighboring grains. These findings enhance the understanding of high-temperature mechanical behavior at both macroscopic and microstructural scales, contributing to the efforts for the design, operation, and life extension of nuclear reactor components.
An evaluation of discrepancies between CPFE simulations and mean-field approximations for dual phase materials
(Wydawnictwa AGH, 2025) Mirhosseini, Shahrzad; Atzema, Eisso H.; van den Boogaard, Antonius H.
This paper explores the discrepancies observed between 2D and 3D crystal plasticity finite element (CPFE) simulations and mean-field approximations in terms of macroscopic flow curves. Two hypotheses are proposed to address the discrepancies: (1) the type of yield function in the mean-field approach, and (2) differences in stress states between the two methodologies. Based on the first hypothesis, the type of yield function may influence the stress-strain partitioning in the mean-field approach. Consequently, the von Mises criterion is replaced with the Hershey yield function. To test the second hypothesis, CPFE simulations are extended to 3D to achieve comparable stress states in both methods. This analysis reveals that the exact shape of the yield function has a marginal impact on the discrepancies, whereas the proper 3D stress distribution significantly reduces them. This comprehensive study also uncovers a limitation of the mean-field approach in terms of accuracy in the prediction of macroscopic material response and stress partitioning for a two-phase polycrystalline material.
Analysis of the decay time and bound-states energies of a particle in a specific structure GaMnAs/GaAs quantum well
(Wydawnictwa AGH, 2025) Ali, Alaa Y.; Ali, Hassan H.; Ali, Mustafa Y.
The bound states and decay time in a certain quantum well structure (GaMnAs/GaAs) were analysed and identified at the minimum decay time. Through the analysis of quantum mathematical equations, we derived specific formulas for energies that significantly amplify the numerical solutions of equations throughout all dimensions of confinement. Without altering the parameters utilized, the quantification, barriers, and well width were predominantly influenced by the spatial dimension parameters, such as the barrier height and well width. The principal bound state and lowest decay time were determined at a well width of 40 Å and a barrier thickness of 46.27 Å. This work revealed a novel characteristic known as interfacial tunnelling, which refers to the phenomenon where an electron establishes a tunnelling state between two interfaces. This tunnelling process is significantly influenced by the characteristics of the materials used, as well as the dimensions of the wells and barriers.