  A stochastic discrete slip approach is proposed to model plastic deformation
in submicron domains. The model is applied to the study of submicron pillar
($D~\leq~1\mu m$) compression experiments on tungsten (W), a prototypical metal
for applications under extreme conditions. Slip events are geometrically
resolved in the specimen and considered as eigenstrain fields producing a
displacement jump across a slip plane. This novel method includes several
aspects of utmost importance to small-scale plasticity, i.e. source truncation
effects, surface nucleation effects, starvation effects, slip localization and
an inherently stochastic response. Implementation on an FFT-spectral solver
results in an efficient computational 3-D framework. Simulations of submicron W
pillars ($D~\leq~1\mu m$) under compression show that the method is capable of
capturing salient features of sub-micron scale plasticity. These include the
natural competition between pre-existing dislocations and surface nucleation of
new dislocations. Our results predict distinctive flow stress power-law
dependence exponents as well as a size-dependence of the strain-rate
sensitivity exponent. The results are thoroughly compared with experimental
literature.
