If, without exception, a periodically changing thermal load acts on a component, this can lead to thermal fatigue. In contrast to thermomechanical fatigue, local thermal expansion is not impeded by external loads or stresses, but by the surrounding areas of the same component at a different temperature. However, since it is irrelevant for the stressed area whether the impairment of thermal expansion is caused by the outside or by the same component, the same load condition could theoretically also be caused by an outside load. In this case, the mechanical and thermal loads would be synchronous. Consequently, thermal fatigue is a special case of thermomechanical fatigue.
The numerical assessment of thermal fatigue is thus carried out in the same way as for thermomechanical damage prediction and is also based on the methods for evaluating low cycle fatigue. Here, too, a coupled multiphysics simulation is required to determine the temperature and stress curve. Since in thermal fatigue, the strain restriction depends solely on the temperature gradient in the component, the most critical, damage-relevant conditions can already be identified from the results of the temperature simulation. In this way, the number of load states required for observation can be significantly reduced and computing time can be saved.