Fatigue behavior prediction of metal alloys based on a unified multiscale crack model

The aim of this paper is to establish a multiscale crack growth model that considers the segmented stages of microstructurally short crack (MSC), physically short crack (PSC) as well as long crack (LC). The proposed multiscale model is based on the crack driving force defined by Chapetti, which briefly accounts for the crack propagation behaviors at MSC stage. Experiments on Ti-6Al-4V titanium alloy are performed. Test data from the experiments and published literatures are essentially in agreement with the predicted curves generated from the multiscale model. Application of the proposed model is further demonstrated by the fatigue life prediction of GH4169 Nickel-based alloy with different initial defects. It is found that, compared with previous models, life prediction results from the multiscale model tend to be more consistent with the test data collected from published literatures, and appear to be relatively conservative. Preliminary analysis indicates that the grain size has significant influence on the fatigue life of Nickel-based alloy that decreases substantially over the grain size increase. The scatter in fatigue lives can be reflected by the variation of grain size. These findings offer certain understanding of crack propagation and fatigue life evaluation to scientific and engineering communities.