Papers by Keyword: Dislocation-Free Zone

Abstract: Stage-I-fatigue-cracks are used as highly localized dislocation sources with well-known Burger’s vectors to study the interaction between dislocations and grain boundaries. This interaction in the plastic zone is of particular interest to understand the fluctuating crack growth in the very short crack regime. In the case of a blocked slip band the dislocations pile up at the grain boundary causing a local stress concentration. The resulting local stress distribution is calculated based on measurements of the dislocation density distribution in the plastic zone. For this purpose the slip line profiles were measured by AFM, the dislocation density distribution was determined and the dislocation-free zone model of fracture (DFZ) was validated. With this it is possible to quantify the grain boundary resistance and to combine geometric and stress approach for grain boundary resistance against slip transfer.

Abstract: In the present paper, a new creep-fatigue crack growth model of J-integral criterion is proposed. The model is built based on the dislocation-free zone (DFZ) theory and cohesive zone model. The process of crack growth is viewed as the intermittent quasi-cleavage fracture of the DFZ. The microscopic void caused by creep will grow and join the dominant crack under creep-fatigue interaction. In this process, material’s plastic deformation induces the change of the dislocation’s density. The redistribution of dislocation will change the value of J-integral within the cohesive zone. When the value of J-integral attains the critical value J_c, crack will grow by the original width of DFZ. Based on it, a simple relation is employed to evaluate crack growth rate under creep-fatigue interaction. The calculated crack growth rate curve exhibits three different regimes, which is in agreement with the general crack propagation pattern under creep-fatigue interaction. The model gives a reasonable explanation for crack growth under creep-fatigue interaction. The calculated value is close to the value obtained by experiment.