Numerical study of inclusion parameters and their influence on fatigue lifetime

The understanding of the influence of inclusion parameters like size, shape and surface roughness on the material's fatigue behavior can provide important guidelines for future material design. In this study, a numerical model is used to calculate the influence of inclusions on fatigue properties. The model consists of the statistical evaluation of numerous representative volume element (RVE) calculations in combination with a crystal plasticity (CP) constitutive model. The RVEs contain inclusions which differ in size, shape, surface roughness and elastic mismatch to the matrix. These parameters have been identified to determine the fatigue lifetime for the case that inclusions are the origin of failure. For each inclusion type, up to 100 RVEs are generated. The RVEs have statistically equivalent distributed microstructural properties but differ in detail, though. The results show that the inclusion size has the biggest influence on the lifetime. The influence of shape and roughness of the inclusion surface is negligible small. The study of the elastic mismatch is matching literature findings. All in all, this study shows that the numerical model can be used to calculate the influence of inclusions on fatigue lifetime. The use of the model can help to reduce the experimental effort for specifying the minimum cleanness requirement of a steel to guarantee the structural integrity under cyclic loading.