Multiscale model prediction of ferritic steel fatigue strength based on microstructural information, tensile properties, and loading conditions (no adjustable material constants)

Abstract

This paper presents a modelling strategy for accurately predicting the high-cycle fatigue strengths of ferritic steels based on only microstructural information, tensile properties, and loading conditions, without any adjustable material constants. The most important feature of the proposed strategy is that total fatigue life is estimated from crack growth life alone. In preparation for model development, the opening/closure behaviour of a microstructurally small crack was quantified from a huge amount of image data obtained by combining an automatic in-situ observation system and a digital image correlation technique. In the proposed modelling strategy, the entire model comprises three sub-models, for: (i) a macroscopic finite element analysis, (ii) microstructure, and (iii) crack growth. The model was strictly validated against the results of experiments performed on three different steels under three different loading conditions (specimen geometries and load ratios). Although the experimental fatigue life results exhibited wide variation, the predicted and experimental data were accurately matched over the entire range. The results demonstrate that the fatigue life of steels under high-cycle fatigue can be accurately predicted from crack growth life alone. Furthermore, the proposed strategy is capable of effectively explaining the dependence of fatigue strength on microstructure and loading conditions based on the fracture mechanics.