  Recently, a dislocation free deformation mechanism was proposed by Kiritani
et al., based on a series of experiments where thin foils of fcc metals were
deformed at very high strain rates. In the experimental study, they observed a
large density of stacking fault tetrahedra, but very low dislocation densities
in the foils after deformation. This was interpreted as evidence for a new
dislocation-free deformation mechanism, resulting in a very high vacancy
production rate.
  In this paper we investigate this proposition using large-scale computer
simulations of bulk and thin films of copper. To favour such a dislocation-free
deformation mechanism, we have made dislocation nucleation very difficult by
not introducing any potential dislocation sources in the initial configuration.
Nevertheless, we observe the nucleation of dislocation loops, and the
deformation is carried by dislocations. The dislocations are nucleated as
single Shockley partials.
  The large stresses required before dislocations are nucleated result in a
very high dislocation density, and therefore in many inelastic interactions
between the dislocations. These interactions create vacancies, and a very large
vacancy concentration is quickly reached.
