The prediction for fatigue strength in very high cycle regime of high strength steel

Abstract

Background:

Fatigue strength is an important parameter of evaluating the material fatigue property. There are many prediction models for fatigue strength in the VHCF regime. Murakami’s model is extensively applied in numerous prediction models. The initiation mode of VHCF cracks in high strength steel is very different from the assumption in Murakami’s model that the internal inclusion is considered as a disc crack.

Objective:

We tried to analyze the effect of inclusion shape on the prediction by Murakami’s model and further examined the prediction effects of several generalized models.

Methods:

We reviewed the prediction models for fatigue strength in the VHCF regime. On the assumption that the fatigue crack which initiated from the internal inclusion is a circumferential crack around a spherical cavity and crack propagation is the critical condition, we modified Murakami’s model. The predicted values of Murakami’s model, the modified model and Liu’s model were compared with the test results of 28 groups of high strength steel in the literature.

Results:

The deviations between predictions by several generalized models and test results are mostly within 20%. The predicted values of four groups of high strength steel by the modified and Murakami’s models and six groups of high strength steel by Liu’s model have large deviations from the test results. The predicted fatigue strength values of Liu’s model are higher than that of the modified model, and the predicted values of the modified model are slightly higher than that of Murakami’s model. The mean value of fitting coefficient C of all types of high strength steel is closer to the coefficient of the modified model, and the sums of squares of coefficient deviations of the modified model is smaller than that of Murakami’s model.

Conclusions:

The effects of inclusion shape on the prediction of fatigue strength in the VHCF regime seem small. Murakami’s model, the modified model and Liu’s model coincide well with the test results in the literature. The prediction effect of the modified model is higher than that of Murakami’s model, and the prediction effect of Murakami’s model is higher than that of Liu’s model.