Thierry Cretegny

Fracture in mode I using a conserved phase-field model

We present a continuum phase-field model of crack propagation. It includes a phase-field that is proportional to the mass density and a displacement field that is governed by linear elastic theory. Generic macroscopic crack growth laws emerge naturally from this model. In contrast to classical continuum fracture mechanics simulations, our model avoids numerical front tracking. The added phase-field smooths the sharp interface, enabling us to use equations of motion for the material (grounded in basic physical principles) rather than for the interface (which often are deduced from complicated theories or empirical observations). The interface dynamics thus emerges naturally. In this paper, we look at stationary solutions of the model, mode I fracture, and also discuss numerical issues. We find that the Griffiths threshold underestimates the critical value at which our system fractures due to long wavelength modes excited by the fracture process.

Multiscale Modeling of Crack Growth in Polycrystals

Recent progress in macroscopic crack growth simulations allows us to attack arbitrary crack growth in complex three-dimensional structures [1]. One of the major deficiencies of the macroscopic description, however, is that it smears out the details of underlying polycrystalline material structure, which can play an important role in the fracture properties of metallic compounds. A polycrystalline metal is inherently inhomogeneous. In particular, the grain boundaries (GBs), which break the local crystalline order, are believed to be the favorable fracture paths in many engineering applications. We therefore need the ability to simulate intergranular crack grow in such a heterogeneous medium. Doing such simulations allow us to study the effects of texture (distribution of grain orientations) and grain geometry on the emerging macroscopic fracture properties. Because one of the key mechanisms at this length scale is the grain boundary (GB) decohesion, we expect the way GBs are modeled to be crucial. However, an accurate constitutive relation is hard to obtain from experimental measurements; this takes us to even lower scales, using atomistic simulations. One of our goals is to understand the effects of grain orientations and misorientations on the grain boundary properties at the atomic scale, and possibly the effects of different chemical compositions.