Abstract
Specimen geometry and loading condition usually have a great influence on the fatigue strength of metallic materials, which is an important issue in evaluating the reliability of component parts. In this paper, a rotating bending fatigue test is performed at first on an hourglass specimen and a notch specimen of a high strength titanium alloy. Experimental results indicate that, in terms of local stress, the notch specimen endures higher fatigue strength in comparison with the hourglass specimen due to its relatively smaller control volume. Then, a probabilistic control volume method is proposed for correlating the effects of specimen geometry and loading condition on the fatigue strength based on Weibull distribution and the concept of control volume. A simple formula is obtained for the fatigue strength in relation to control volumes, in which the parameter is the shape parameter of Weibull distribution of fatigue strength. The predicted results are in good agreement with the present experimental data for high strength titanium alloy and the data for the high strength steel and the full scale EA4T axle in the literature.
Highlights
The effects of specimen size, notch geometry, and loading condition on fatigue behavior of metallic materials are important topics in the fatigue research field, which is of great importance in evaluating the fatigue strength of structure components
Furuya [9] investigated the effect of specimen size on the very high cycle fatigue behavior of high strength steels, and showed that large specimens endured lower fatigue strengths due to the appearance of larger inclusions in control volumes
The fatigue notch factor Kf and the elastic stress concentration factor Kt were correlated by Kf /Kt = (Vn /Vs )a, where Vn and Vs were volumes for the notched and smooth specimens, respectively, and a was a material constant determined by fitting the fatigue strength and the highly stressed volume
Summary
The effects of specimen size, notch geometry, and loading condition on fatigue behavior of metallic materials are important topics in the fatigue research field, which is of great importance in evaluating the fatigue strength of structure components. Much research has been carried out on the effects of specimen geometry and loading condition on fatigue behavior of metallic materials [1,2,3,4,5,6,7,8]. Kuguel [10] introduced a highly stressed volume method for predicting the fatigue strength of notched specimens. Lin & Lee [11] studied the effect of highly stressed volume on the fatigue strength of austempered ductile irons under rotating bending and axial loading fatigue tests, and showed that the highly stressed volume method was able to predict the effects of notch and loading condition on fatigue strength. It was indicated that the highly stressed surface concept might be preferably applied in case of surface failure modes, while for the highly stressed volume concept, an upper threshold value was needed in advance
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