Local lattice instability at a dislocation nucleation and motion

By means of molecular dynamics technique, the dynamic process of nucleation and motion of a partial dislocation is carefully investigated in a nanoscopic specimen of single crystalline nickel under [001] tension. The mechanism and mechanics are discussed in a new light of the two successive unstable behaviors of local lattices observed in the homogeneously deformed body ; the first unstable behavior is the collapse of local lattices that breaks the homogeneous Poisson's contraction, leading to the deformation concentration. The second is the unstable shear of lattices on a slip plane in the deformation concentrated region. The nucleation and glide of dislocation can be observed as the migration of atoms on the slip plane as a result of these unstable behaviors. The criteria of the onset of the unstable behaviors are evaluated based on the elastic stiffness coefficients, Bijkl. That is, the instability criteria proposed by Wang et al. [Wang, J. et al., Phys. Rev. Lett. 71-25 (1993), 4182- 4185] are adopted to evaluate local instability. The results show that the elastic stiffness of the first and second unstable behaviors becomes negative at each onset. Thus, the local lattice instabilities cause the dislocation nucleation and motion and can be quantitatively evaluated by the negativeness of local Bijkl