Prediction of Low-Cycle Fatigue Life Based on Uncoupled Ductile Fracture Criteria

Date

2024-9

Author

Gündüz, Ozan

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Classical life prediction methods to determine fatigue failure require extensive testing, which increases costs and time. This thesis aims to estimate low-cycle fatigue failure by developing a fatigue failure criterion (FFC) based on uncoupled ductile fracture criteria (UDFC) and numerical simulations of tensile test specimens made of the relevant materials. For this purpose, five energy-based UDFC namely Freudenthal, Cockroft-Latham, Ayada, Oyane-Sato, and Oh are used. A user-defined subroutine is written and implemented to FEA software for calculating the damage accumulation related to these criteria for both quasi-static and cyclic loading. Then, damage accumulation values of both the tensile test simulations and fatigue simulations for the sample material are obtained and compared using the mentioned five UDFC. Fatigue simulations are carried out for different stress amplitude, mean stress and frequency values. All comparisons are conducted by referring to the values obtained at the onset of necking which is determined by the stress wave propagation method. As a result, an equation is obtained that defines the failures calculated by these five UDFC under various stress amplitude and mean stress values. This equation is called as fatigue failure criterion function and can be presented by a surface to define the failure. FFC function is also used to determine the fatigue life for the low-cycle by another relation called the life function. Finally, this function is applied to determine the FFC for fatigue failure. It is observed that damage accumulation can be calculated using FFC with acceptable accuracy.

Subject Keywords

Low-Cycle Fatigue, Plasticity, Ductile Damage, Life Prediction, Stress Wave Propagation Method

URI

https://hdl.handle.net/11511/111324

Collections

Graduate School of Natural and Applied Sciences, Thesis