Incorporating Residual Stresses Into Thermo-Mechanical Fatigue Analysis of Cylinder Head

Residual stresses are one of the key factors affecting fatigue durability of important cast parts such as cylinder head and engine block. In automotive industry, general approach is to incorporate residual stresses into durability analysis by simply superposing the values by means of a fatigue post-processor. Residual stresses elevate or decrease the mean stress value according to whether stress states are tensile or compressive. However, it is thought that uncoupling two analyses may lead to misleading results. Instead, a single analysis should incorporate residual stress and thermo-mechanical analysis steps, one after the other. This is a comparative study for these two approaches and shows that assumption of a virgin material at the beginning of thermo-mechanical analysis is not always valid although two approaches agrees well with each other for moderate loading levels.