ICAMS / Interdisciplinary Centre for Advanced Materials Simulation

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Studies of fatigue crack propagation: a multiscale cohesive zone model

Date: 16.08.2009
Place: International Conference on the Strength of Materials, Dresden, Germany

Steffen Brinckmann

The propagation of fatigue cracks is governed by the presence of plastic strains and plastic strain gradients in the vicinity of the crack tip. Statistically stored and geometrically necessary dislocations are related to these measures of deformation and are responsible for crack advance as well as for crack tip shielding. We introduce a novel multiscale cohesive zone model for the description of fatigue crack growth in metals. The model incorporates the information from the microscale, i.e. dislocation distribution, into the constitutive model of the cohesive zone, i.e. macroscopic continuum model. The combination of stresses due to the dislocation distributions and stresses due to the applied boundary conditions leads to stresses in excess of the cohesive strength of the metal (10GPa). A fatigue crack growth threshold and Paris law dependence of the fatigue crack growth rate on ?K are outcomes of the model. Overload is discussed with respect to the dislocation density distribution and the resulting fatigue crack growth retardation. Significant crack closure is observed. The obtained dislocation densities compare well with results from discrete dislocation simulations. The macroscopic results agree with experimental findings of fcc metals.

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