| In this work, the deformation process in FCC single crystals under high strain rate ranging between 105 s-1 to 108 s-1 is investigated using a multiscale model of plasticity that couples discrete dislocation dynamics and finite element analyses. Computer simulations are carried out to mimic the shock loading condition involved in high intensity laser experiments. In the first part of this study, the effects of peak pressure, shock pulse duration, crystal anisotropy and the nonlinear elastic properties on the interaction between shock waves and preexisting dislocation sources are investigated. Our calculations show that the dislocation density is proportional to strain rate, pulse duration and crystal orientation, and that the dislocation density increases with pressure proportional to a power law of 1.70 for pressure greater than 30 GPa. The results suggest that while the inclusion of pressure-dependent elastic properties for isotropic media leads to faster wave propagation speed, incorporating the effect of crystal anisotropy in the elastic properties results in orientation dependent wave speed and peak pressure. The relaxed configurations of dislocation microstructures showed the formation of micro bands coincident with the {lcub}111{rcub} whose characteristics are strain rate and orientation dependent.; In the second part of this study, shock-induced dislocation nucleation is investigated. Shock waves with strength ranging from 10 to 60 GPa are launched in copper perfect crystals resulting in the nucleation of large number of dislocation loops at the wave front. Once the dislocation loops are nucleated, they grow in all directions in their slip planes forming a three dimensional microstructures consisting of dislocation entanglements and weak cellular structure. By this plasticity mechanism, we found that uniaxially compressed material relaxes to a hydrostatically compressed state (1D → 3D) as observed in the experiment.; In the third part of this study, the effect of finite element boundary condition on wave propagation is investigated by implementing periodic boundary condition and comparing its results with free and confined boundary conditions. The results show that confined and periodic boundary conditions based on node-to-node matching are suitable to model shock wave propagation. Mesh sensitivity analyses for steep and ramp shock waves show that the convergence in the ramp wave occurs at relatively coarse mesh density when compared to the steep wave. The effect of lattice rotation on strain localization was also investigated. The results show that more strain localization occurs when slip rotation is taken into account. |
