A representative volume element (RVE) based multi-scale method is proposed to investigate the mechanism of fatigue crack propagation by the molecular dynamics (MD) and the extended finite element methods(XFEM) in this study. An atomic model of carbon steel plate is built to study the behavior of fatigue crack at the micro scale by MD method. Then the RVE model for fatigue crack propagation should be built by fitting the data which was obtained from the MD result with the Paris law model. Moreover, the effect of micro-structural defects including interstitial atoms, vacancies have also been considered in this study. The results indicate that the micro-structural defects can deeply influence the values of Paris law constants and the life of the specimen can be evaluated by the proposed method.
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