SIMULATION OF THE BRITTLE-DUCTILE TRANSITION IN SILICON SINGLE-CRYSTALS USING DISLOCATION MECHANICS

A numerical model is developed to characterize the physical process of the brittle-ductile transition (BDT) in Si single crystals. The model considers a symmetric dislocation emission at a crack tip in {110}[11 0]-oriented specimens. The motion of individual dislocations is assume d to be driven by the resolved shear stress and follows an Arrhenius l aw. Numerical simulations are performed, and the shielding to the crac k tip by the emitted dislocations is evaluated. The simulations are te rminated either when the crack tip stress intensity reaches the intrin sic fracture toughness (brittle fracture), or when the far field appli ed stress intensity reaches a critical value significantly higher than the intrinsic toughness (ductile failure). Simulation results show th at, when two slip systems are activated simultaneously, a sharp BDT be havior results. The dramatic increase in Fracture toughness during the BDT is attributed to the sudden increase in the number of dislocation s emitted from the crack tip. The model predictions are consistent wit h experimental observations. The results also indicate that the number of active slip systems at the crack rip plays an important role in de termining the behavior of the BDT. While activation of multiple slip s ystems gives rise to a sharp transition, a single active slip system w ill result in a gradual transition. This conclusion may explain some r ecent experimental observations. (C) 1997 Acta Metallurgica Inc.