The influence of multiple slip systems on the brittle-ductile transition in silicon

The brittle-ductile transition results from the competition between cleavage fracture and dislocation activities at or near the crack tip. In the present paper a 2-dimensional dynamic dislocation simulation is performed. The material properties used in the simulation are those of single crystalline silicon. Dislocations are assumed to emit from an atomically sharp cleavage crack along different symmetrically placed slip systems. Individual dislocations move away from the crack tip following an Arrhenius law driven by the net resolved shear stress. The dislocations shield the crack tip from the increasing far field stress intensity. Brittle fracture occurs when the crack tip stress intensity reaches the intrinsic fracture toughness. Ductile failure is assumed to occur if the far field stress intensity reaches a critical value significantly higher than the intrinsic toughness. The study focuses on the influence of interaction forces between dislocations in different slip systems. With all interactions fully accounted for, the simulations show that the activation of multiple slip systems results in a sharp transition whereas the activation of a single symmetric pair results in a gradual transition.