Discrete dislocation dynamics study of dislocation microstructure during cyclic loading

The role of loading conditions, grain morphology and crystallographic orientation on the dislocation microstructure evolution in fcc metals under high frequency cyclic loading is studied by three-dimensional discrete dislocation dynamics simulations. The formation of characteristic dislocation structures, e.g. prismatic loops, dipolar structures and debris clusters is analyzed based on a graph analysis of the dislocation network. The type of defects formed is found to be independent of the loading amplitude. Very early stages of structure formation are only observed for larger amplitudes. Furthermore, a threshold in loading amplitude has to be reached to increase the rate of defect formation and dislocation density. Also, the grain morphology has a major impact on dislocation multiplication, comparing grains with a shape of a cube or a truncated dodecahedron. Surface grains generally show more pronounced irreversibility, due to the asymmetry for dislocation motion. The free surface acts as dislocation sink, thus causing increased irreversibility. The overall mechanical response can be characterized by an effective lower stiffness for larger strain amplitudes, as a strong anelastic behavior is observed.