  A theoretical and computational investigation is carried out of a dissipative
model of rate-independent strain-gradient plasticity and its regularization. It
is shown that the flow relation, when expressed in terms of the Cauchy stress,
is necessarily global. The most convenient approach to formulating the flow
relation is through the use of a dissipation function. It is shown, however,
that the task of obtaining the dual version, in the form of a normality
relation, is a complex one. A numerical investigation casts further light on
the response using the dissipative theory in situations of non-proportional
loading. The elastic gap, a feature reported in recent investigations, is
observed in situations in which passivation has been imposed. It is shown
computationally that the gap may be regarded as an efficient path between a
load-deformation response corresponding to micro-free boundary conditions, and
that corresponding to micro-hard boundary conditions, in which plastic strains
are set equal to zero.
