Abstract

We have so far performed many molecular dynamics simulations on various pseudo-polycrystalline and amorphous nickels under tension, suggesting that neither the system nor the atomic elastic stiffness coefficients, or the global and local stabilities, could predict the “macroscopic” yield of disordered systems. The previous simulations, however, are implemented under the displacement control so that it would not be the force balance but the geometrical requirement that dominates the yield. In order to clarify the effect of external loading condition, we have achieved the tensile simulations again with the force control condition. The effect of the constraint on the transverse Poisson' contraction is also investigated. Contrary to the previous report, the stress-strain peak exactly coincides with the point where the deviation of local stability vanishes and the determinant of both the system and atomic elastic stiffness coefficients becomes zero, under the force control condition without Poisson' contraction. The system and local stabilities also well predict the stress drop under the displacement control without Poisson' contraction. On the other hand, the dynamic loading leads an unrealistic elongation under the force control condition with Poisson' contraction ; however, the local stability definitely points out the onset of the rapid elongation while the system one merely does that of dilatation after the unrealistic elongation.

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