The effects of long-range and short-range interactions on the early stress--strain response and dislocation density evolution in hexagonal close-packed (hcp) metals are studied using three-dimensional discrete dislocation dynamics (DD). To examine long-range interactions, the DD code is developed such that elastic stress fields between interacting dislocations are calculated by either enforcing elastic isotropy or considering the actual elastic anisotropic constants of the hcp metal. To improve treatment of short-range interactions, a set of local rules for the behavior of closely interacting dislocations is implemented. In particular, a new scheme for elastic repulsion in the event of repulsive short-range interactions is presented and found to have a significant effect on the stress--strain response and dislocation density evolution. Large-scale simulations are performed for three hcp single crystals (Hf, Mg and Zr) in c -axis tension to examine the effect of elastic anisotropy on the collective response of several interacting dislocations. It is found that departure from isotropic elasticity has a substantial effect on strain hardening, particularly for Hf.
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