A numerical description of short fatigue cracks interacting with grain boundaries

Short fatigue cracks typically propagate in stage I in which interaction with grain boundaries results in a fluctuating crack growth rate. Although there are established models, like the Bilby-Cotrell-Swinden theory and the Weertman model for crack growth and the model of Tanaka and Navarro and De Los Rios for their interaction with grain boundaries, a quantitative description of fatigue resistance is lacking. A unique technique combining focused ion beam based artificial crack initiation and three-dimensional tomography was used to separate the different influences of crack parameters and grain boundary parameters. The mechanisms which determine the strength of a grain boundary against crack propagation were thereby identified. Finally, it is shown how the models mentioned above can be easily used to calculate crack propagation through a grain boundary from single-crystal data and the orientation of the neighbouring grains only. This gives a promising perspective to improve fatigue life prediction and fatigue resistance of cyclically loaded materials.