ICAMS / Interdisciplinary Centre for Advanced Materials Simulation
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Studying fatigue crack initiation at different scales

Date: 29.06.2009
Place: ICAMS, Ruhr-Universität Bochum, Germany

Steffen Brinckmann

In recent years, much progress has been made in the domain of fatigue crack propagation of metals, where the global stress intensity factor range has been identi ed as the dominating factor. For fatigue crack initiation, SEM observation revealed that the evolution of distinct dislocation distributions and surface roughness are key ingredients in fatigue crack initiation. In this presentation, I will present two computational frameworks that focus on this damage mechanism. The rst framework ties together dislocation dynamics, the elastic elds due to crystallographic surface steps and cohesive surfaces to model near-atomic separation leading to fracture. Cyclic tensioncompression simulations are carried out where a single plastically deforming grain at a free surface is surrounded by elastic material. While initially the cycle-by-cycle maximum cohesive opening increases slowly, the growth rate at some instant increases rapidly, leading to fatigue crack initiation at the free surface and subsequent growth into the crystal. This rst study also sheds light on random local microstructural events which lead to premature fatigue crack initiation. The second framework is currently developed at ICAMS. It ties together dislocation dynamics and molecular dynamics to establish a concurrent multiscale model, which will be introduced. Special emphasis will be placed on the description of the interface that links these models of di erent spatial and temporal domains.

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