A thermo-mechanical fatigue damage model for variable temperature and loading amplitude conditions

A fatigue life prediction method for thermo-mechanical fatigue damage under variable temperature and loading amplitudes was proposed. In this approach, a rainflow cycle counting technique was used to extract cycle counts from the mechanical loading history. For each loading cycle, an equivalent damage temperature was determined. Once the equivalent temperature was used, the loop would be guaranteed closed. This approach was based on the assumption that total fatigue damage is defined as the summation of mechanical fatigue damage and oxidation damage. The mechanical fatigue damage was calculated based on the Smith–Watson–Topper (SWT) model at room temperature, while the oxidation damage was calculated based on the Sehitoglu model determined from the stress/strain data at the equivalent temperature. Finally, Miner’s linear damage rule was used for damage accumulation. A case study with automotive exhaust systems was conducted to verify the effectiveness of the proposed method. The effect of creep damage was excluded in this study.