Abstract：Metallic single crystals, which are widely used in industrial devices due to their excellent properties, make it a necessary task to study the mechanical behavior of metallic single crystals. Dislocation evolution affects the plastic deformation and fracture of crystals, while the nucleation and evolution of dislocations are related to the crystal orientation. Investigating the mechanism of the influence of crystal orientation on the elastoplastic cracking process, especially from the perspective of dislocation evolution and interaction between dislocations and cracks, has great significance in solving the challenging problems of elastoplastic fracture and brittle-ductile transition in metallic crystalline materials. However, the classical continuum mechanics framework has singularity problems when dealing with discontinuities such as cracks. In this paper, the Mode I elastoplastic fracture of a single crystal for four different orientations is investigated by using the superposition scheme for discrete dislocation dynamics (DDD) in the framework of peridynamics (PD). As a nonlocal alternative framework to classical continuum mechanics, PD models use spatial integration instead of spatial derivative, making it well-suited for problems where discontinuities may occur and develop. Moreover, PD models allow for integrating possible nonlocal effects induced by dislocations/microstructure/damage and their evolution. Therefore, the DDD-PD model can simulate elastoplastic fracture by considering the autonomous interactions between dislocations and crack growth. For obtaining the results, neither a preset cracking path nor a cohesive zone model is needed. The results show that the mechanical behavior of a single crystal under Mode I fracture exhibits evident orientation dependence, meaning that orientation change leads to differences in the crystal's toughness, critical applied strain, and fracture behavior. The simulation reproduces the brittle-ductile transition behavior in the facture of single crystals, which is related to the nucleation and motion of the dislocations near the crack tip. The numerical elastoplastic deformation and facture results also capture the Schmid factor dependence. Dislocations tend to nucleate and glide on the slip planes with a larger Schmid factor. We show that the distribution and evolution of dislocations on the slip system, affecting the crystal fracture pattern, vary with the crystal orientation.
2023, Vol. 44 
