The gigacycle fatigue strength of steels: a review of structural and operating factors

Abstract

It is known that usual frequency up to 100 Hz has no influence on the high cycle fatigue (HCF) strength of steels. However, in the very high cycle fatigue (VHCF) regime, the frequency effect is still unclear. Indeed, a high frequency can lead to heating, instability of the microstructure and degradation or improvement of the mechanical properties of the material, which in turn depend on the type of loading and on the operating environment. Based on a large literature review of many experimental data in gigacycle regime, a synthesis is proposed to discuss the effect of the structural and operational factors on the VHCF characteristics of low and high strength steels (Jeddi et al. (2018)). Failure mechanisms in HCF and VHCF (surface or internal crack initiation) are related to S-N curve shape. The effect of the microstructural and mechanical features on the VHCF resistance is debated depending on different parameters: microstructure, inclusion size, inclusion type and depth, hydrogen, environment, maximum tensile strength of the steel and residual stresses. The influence of the loading conditions on the VHCF strength is addressed by taking into account both the loading frequency effect, the highly stressed volume, the loading type and loading ratio. Finally, the influence of the testing techniques (pulse-pause or continuously cyclic loading) is discussed.