Mechanismenorientierte Modellierung und Simulation der mikrostrukturbestimmten Kurzrissausbreitung unter Berücksichtigung ebener und räumlicher Aspekte

In this thesis two mechanism-based models are presented, which simulate the propagation of microstructurally short fatigue cracks. The first one is a two-dimensional approach based on experimental investigations on titanium Ti6Al4V that describes stage I-crack growth in this widely used alloy. The model allows for crack propagation on slip planes and grain boundaries due to partially irreversible plastic deformations at the crack tip and considers grain boundaries as obstacles to crack extension. It is validated by simulating the growth of real fatigue cracks and applied to predict crack propagation in virtual microstructures. Here, simulation results show a good agreement between the calculated number of cycles to failure and fatigue test data.
In the second part of this thesis a three-dimensional model for stage I-crack propagation is presented, which offers significant advantages compared to two-dimensional approaches. It allows for a more realistic description of short crack growth by considering the finite depth of surface cracks as well as the real three-dimensional orientation of the slip planes and the resulting misorientation between slip systems in adjacent grains. The three-dimensional crack problem is solved numerically using finite dislocation loop boundary elements. The model is applied to analyse the influence of the factors mentioned above on the crack propagation rate and to show the advantages in comparison to simplified two-dimensional approaches.