Verbesserung der Bruchzähigkeit spröder Materialien durch den gezielten Einbau von Materialinhomogenitäten

This thesis aims to increase the fracture toughness of brittle materials by inserting voids. A void is a local material inhomogeneity, which attracts a crack that propagates in its vicinity, forcing the crack to run into the void and get trapped. This allows the increase of the external load. The idea of this work is to apply this crack trapping mechanism to enhance the fracture toughness without further crack propagation of intrinsically brittle materials under uniaxial and multiaxial loading conditions. The aim is to find effective void arrangements that are able to trap all cracks that might originate from the surface of a structural component. In order to maintain a high material stiffness, the void volume shall be as small as possible. The investigation considers voids of different shapes as well as the combination of voids with stiff particles. For this purpose, a numerical method, called the crack trajectory interpolation (CTI) method, is developed in this thesis to efficiently analyze a large number of crack paths in the vicinity of a void and a particle. In this way, different design parameters, such as the trapping zone size of a void and the crack repulsion area of a stiff particle, are determined for different void and particle shapes. A damage-based modeling approach is used to determine the increase in fracture toughness after a crack has been trapped inside a void. The CTI-method is extended by a linear superposition approach in order to find arrangements of voids, as well as combinations of voids and particles, that intercept all cracks in the material. The increase in fracture toughness through different arrangements is determined by a damage-based approach. Hereby is assumed that the voids have a surface defect due to the manufacturing process, and the fracture toughness improvement is determined as a function of the defect size. By linking the fatigue crack growth rate to the crack driving force, the CTI-method is extended to model cyclic crack growth. This enables the estimation of the fatigue life of a crack growing in a material with stiff particles or voids.