| Popis: |
Yielding behavior in amorphous solids has been investigated in computer simulations employing uniform and cyclic shear deformation. Recent results characterise yielding as a discontinuous transition, with the degree of annealing of glasses being a significant parameter. Under uniform shear, discontinuous changes in stresses at yielding occur in the high annealing regime, separated from the poor annealing regime in which yielding is gradual. In cyclic shear simulations, relatively poorly annealed glasses become progressively better annealed as the yielding point is approached, with a relatively modest but clear discontinuous change at yielding. To understand better the role of annealing on yielding characteristics, we perform athermal quasistaic cyclic shear simulations of glasses prepared with a wide range of annealing in two qualitatively different systems -- a model of silica (a network glass), and an atomic binary mixture glass. Two strikingly different regimes of behavior emerge: Energies of poorly annealed samples evolve towards a unique threshold energy as the strain amplitude increases, before yielding takes place. Well annealed samples, in contrast, show no significant energy change with strain amplitude till they yield, accompanied by discontinuous energy changes that increase with the degree of annealing. Significantly, the threshold energy for both systems correspond to dynamical crossover temperatures associated with changes in the character of the energy landscape sampled by glass forming liquids. Uniform shear simulations support the recently discussed scenario of a random critical point separating ductile and brittle yielding, which our results now associate with dynamical crossover temperatures in the corresponding liquids. |
