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A micromechanical model of creep induced grain boundary damage is proposed, which allows for the simulation of creep damage in a polycrystal with the finite element method. Grain boundary cavitation and sliding are considered via a micromechanically motivated cohesive zone model, while the grains creep following the slip system theory. The model has been calibrated with creep test data from pure Cu single crystals and a coarse-grained polycrystalline Cu-Sb alloy. The test data includes porosity measurements and estimates of grain boundary sliding. Finally, the model has been applied to Voronoi models of polycrystalline structures. In particular the influence of grain boundary sliding on the overall creep rate is demonstrated.
The stress States of components under Service conditions differ in general from the loading conditions that are routinely applied during material testing. When data that results, e.g., from uniaxial testing should be used for lifetime assessment, a good understanding of the failure behaviour in dependence of the stress state is necessary. For polycrystalline materials under high temperature loading, the development of creep damage is one important factor that limits a component’s lifetime. For cases where creep damage is related to the nucleation and growth of grain boundary cavities, the local normal stress acting on a grain boundary has been found to have a strong influence on the damage development. Hence, creep damage is usually localized along planes that lie perpendicular to the maximum principal tensile stress.