**Computational nanoscale plasticity simulations using embedded atom
potentials**

M. F. Horstemeyer, M. I. Baskes, S. J. Plimpton, Theoretical and Applied Fracture Mechanics, 37, 49-98 (2001).

In determining structure-property relations for plasticity at
different size scales, it is desired to bridge concepts from the
continuum to the atom. This raises many questions related to volume
averaging, appropriate length scales of focus for an analysis, and
postulates in continuum mechanics. In a preliminary effort to evaluate
bridging size scales and continuum concepts with discrete phenomena,
simple shear molecular dynamics simulations using the embedded atom
method(EAM) potentials were performed on single crystals. In order to
help evaluate the continuum quantities related to the kinematic and
thermodynamic force variables, finite element simulations (with
different material models) and macroscale experiments were also
performed. Various parametric effects on the stress state and
kinematics have been quantified. The parameters included the
following: crystal orientation (single slip, double slip, quadruple
slip, octal slip), temperature (300 and 500 K), applied strain rate
(10*sup 6*-10*sup 12* s*sup -1*), specimen size (10 atoms to 2 mu m),
specimen aspect ratio size (1:8-8:1), deformation path (compression,
tension, simple shear, and torsion), and material (nickel, aluminum,
and copper). The yield stress is a function of a size scale parameter
(volume-per-surface area) that was determined from atomistic
simulations coupled with experiments. As the size decreases, the yield
stress increases. Although the thermodynamic force (stress) varies at
different size scales, the kinematics of deformation appears to be
very similar based on atomistic simulations, finite element
simulations, and physical experiments. Atomistic simulations, that
inherently include extreme strain rates and size scales, give results
that agree with the phenomenological attributes of plasticity observed
in macroscale experiments. These include strain rate dependence of the
flow stress into a rate independent regime; approximate Schmid type
behavior; size scale dependence on the flow stress, and kinematic
behavior of large deformation plasticity.

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