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Cylindrical specimens of CrCoNi alloy with electropolished surfaces were subjected to constant total strain amplitude low cycle fatigue. The alloy exhibited an initial period of cyclic hardening followed by cyclic softening until failure occurred. At the end of hardening stage at the peak of cyclic stress, well-developed persistent slip markings (PSMs) consisting of extrusions and intrusions were associated with thin deformation twins. A sophisticated experimental workflow was designed to extract information from the surface and the bulk of tested material. A combination of SEM, EBSD, ECCI, FIB and HR-STEM was used to study the internal structure and the surface profiles around the deformation twins, which were produced during the initial period of cyclic loading. Furthermore, localized cyclic plastic strain and stress concentrations near deformation twins led not only to early, well-developed PSMs, but also to the activation of TWIP and TRIP plasticity even at low macroscopic stress amplitudes.
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This content will become publicly available on April 1, 2026
Optimizing the combined isotropic/kinematic hardening parameters of pressure vessel materials and welds using the incremental elastic-limit approach
In this work, a novel optimization approach is introduced to extract combined hardening parameters from the cyclic stress-strain data obtained from the initial hardening cycles of isothermal, low-cycle fatigue tests. The incremental elastic-limit (IEL) concept is proposed due to the often-undiscernible elastic range of a stabilized stress-strain cycle, that increases the complexity of hardening parameters optimization. The optimization process is implemented by taking an iterative search for the elastic range by a fixed elastic limit increment, and the corresponding hardening parameters are obtained using the nonlinear fitting algorithms in the MATLAB™ Software. An implicit stress-update function is introduced to simulate the cyclic stress and strain with a given set of hardening parameters and yield strength. The fitness of the optimization is calculated based on the least square difference between the experimental and simulated stress-strain data. Furthermore, the IEL concept is incorporated to optimize the cyclic hardening parameters. In the final step, finite element (FE) analysis using the optimized hardening parameters is applied to demonstrate the effectiveness of the IEL approach. The proposed methodology is applied to pressure vessel steels and Ni-based weld metals.
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- PAR ID:
- 10591312
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- International Journal of Pressure Vessels and Piping
- Volume:
- 214
- Issue:
- C
- ISSN:
- 0308-0161
- Page Range / eLocation ID:
- 105407
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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