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Abstract

On the microstructural scale, cyclic plasticity is governed by the generation, motion and interaction of dislocations. Especially in the high cycle fatigue regime, experiments have shown that major parts of the material life time are attributed to fatigue crack incubation and microstructurally influenced small fatigue crack growth. Fatigue crack incubation in polycrystalline materials is determined by the accumulation of irreversible deformation. Thus, it is important to properly model the mechanisms and criteria for crack initiation, which are strongly influenced by the accumulated irreversible deformation.

In the scope of this work, micromechanical modeling is applied to predict crack initiation within a realistic microstructure. The method is based on a simulation framework for microstructurally informed fatigue crack simulations of polycrystalline materials. It consists of three main constituents: (i) generation of material microstructures as representative volume elements (ii) implementation of a phenomenological crystal plasticity model capturing relevant hardening mechanisms important for cyclic loading conditions, and (iii) analysis of fatigue indicator parameters within the model. In particular that latter allows us to study fatigue crack initiation and the early stages of microstructurally influenced fatigue crack growth. The established micromechanical modeling framework is applied to study fatigue crack initiation for predicting Wöhler diagrams.

Furthermore, the influence of different microstructural parameters on the small fatigue crack growth is investigated. The material parameters for crystal plasticity are adapted from the literature and the results of the simulations are used to establish a general understanding of micromechanical mechanisms during fatigue loading.