Title: Phase field simulations for fatigue failure prediction in processing
Name: Christoph Schreiber
Phone: 0631 – 205 - 2126
Fracture mechanics of solids is a main issu within technical applications. A formulation of the entire failure process, from crack nucleation over crack extension until failure, is covered by the phase field method. In contrast to conventional fracture simulation methods phase field modeling of fracture deals with the minimization of the total energy and therefore needs no additional criteria for the prediction of the crack propagation direction. The approach has successfully been applied to quasi-static and dynamic brittle fracture. Extensions for elastoplastic material models also exist. However, for cyclic loading it is known, that crack initiation and growth takes place for maximum loads below critical values found in quasi-static tests. So far only very little research was concerned with the application of a phase field fracture model to this so called cyclic fatigue process. As cyclic loads appear in many manufacturing processes, such as turning and milling, the extension and application of the developed phase field model is in the focus of the present research project.
In order to take the effect of cyclic fatigue into account, an existing phase field model shall be expanded with the purpose to enable the simulation of fatigue crack growth. This will require a modification of the so called evolution equation for the order parameter (crack field) to integrate cyclic mechanisms into the phase field formulation. The extension will have to resemble standard fatigue crack growth models, such as the Paris law. Important properties of the fatigue phenomena such as the effects of size, load ratio, and sequence of load cycles also shall be included in the formulation. In the cycle domain the formulation has to be able to handle the exceedingly high number of load cycles to failure which can occur before macro crack initiation or failure takes place.
A phase field model is developed that can be used to simulate cyclic fatigue failure in manufacturing processes. The model is expected to predict lifetimes of tools in manufacturing processes and failure scenarios of work piece due to cyclic loadings.