Considerable efforts have been conducted on the modeling of fatigue crack growth (FCG), aiming at an accurate prediction of fatigue life. However, due to the influence of microstructure, it is still challenging to describe FCG behavior, especially for small cracks. The FCG exhibits obvious variation at small crack growth procedure. In this regard, a probabilistic model by integrating N-R model is proposed to simulate the FCG process at stage I. The concerned material is nickel based superalloy GH4169. The proposed model involves both macroscopic and microscopic material parameters for the extension of dislocation with the impediment from grain boundary. Random grain size is represented by the fluctuation of FCG rate. Model validation is performed by comparing the simulation results and experimental data. It is revealed that the dependence tends to be less prominent on longer crack length, smaller grain size and higher applied stress.
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