Basic Mechanisms Leading to Fatigue Failure of Structural Materials

Abstract

General features of the damage evolution in cyclic loading of structural materials are summarized. The attention is paid to the comparison of the damage mechanisms in materials that are used for service both at room and at elevated temperatures, namely austenitic stainless steel Sanicro 25. Principal mechanisms leading to fatigue fracture at room and at elevated temperature are documented. While cyclic slip localization is a decisive process in the initiation of fatigue cracks at room temperature, the localized oxidation plays an important role in isothermal high temperature cyclic loading. Specific mechanisms of the early fatigue damage in thermomechanical cyclic loading are studied. The in-phase thermomechanical loading leads to the intergranular crack initiation due to preferred grain boundary oxidation and intergranular crack growth. The out-of-phase thermomechanical loading results in oxide cracking and localized oxidation of the metal in the area of cracked oxides and to transgranular crack growth. The damage mechanisms can explain differences in fatigue life under various loading and temperature conditions.