Microstructure-Based Fatigue Modeling with Residual Stresses : Effect of Inclusion Shape on Very High Cycle Fatigue Life

Funding Information: Funding: This work was financially supported by the Fundamental Research Funds for the Central Universities (No. FRF-TP-20-026A1), the special grade of China Postdoctoral Science Foundation (No. 2021T140050), and the State Key Laboratory of Advanced Metallurgy Foundation of China (No. 41621014). Publisher Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland.When considering the effect of inclusions on fatigue life, the size effect of inclusions is well recognized. However, many of these studies overlooked or decoupled the size effect from the shape features. Therefore, in this study, the influence of the shape characteristics of inclusions with 3 equivalent sizes of 26.6 µm, 13.3 µm, and 4.2 µm on the very high cycle fatigue life of high-strength steels is investigated based on a microstructure-sensitive modeling approach, considering residual stresses. A shape parameter, unifying the aspect ratio and tilting angle of inclusion, is introduced. Based on this parameter, a new formulation of fatigue life with respect to inclusions is also proposed, extending the former one to consider the shape effect of inclusions. It is concluded that the general trend that the fatigue life increases with the decrease in inclusion size is still valid, while the shape features in terms of aspect ratio and tilting angle complicate the quantitative influence of inclusions size significantly. Even for a constant inclusion size, the combination of shape factor and tilting angle could change the fatigue life with one order of magnitude compared with the commonly assumed round shape. These findings would enhance the precision for the fatigue life estimation based on pre-inclusion analysis and also eventually provide new dimensions for inclusion engineering to improve fatigue resistance, as size will not be the only design parameter for fatigue life.Peer reviewe