  Previous studies demonstrate that grain-boundary sliding could accelerate
creep rate and give rise to large internal stresses that can lead to damage
development, e.g. formation of wedge cracks. The present study provides more
insight into the effects of grain-boundary sliding (GBS) on the deformation
behaviour of realistic polycrystalline aggregates during creep, through the
development of a computational framework which combines: i) the use of
interface elements for sliding at grain boundaries, and ii) special triple
point (in 2D) or triple line (in 3D) elements to prevent artificial dilation at
these locations in the microstructure with iii) a physically-based crystal
plasticity constitutive model for time-dependent inelastic deformation of the
individual grains. Experimental data at various scales is used to calibrate the
framework and compare with model predictions. We pay particular consideration
to effects of grain boundary sliding during creep of Type 316 stainless steel,
which is used extensively in structural components of the UK fleet of Advanced
Gas Cooled Nuclear Reactors (AGRs). It is found that the anisotropic
deformation of the grains and the mismatch in crystallographic orientation
between neighbouring grains play a significant role in determining the extent
of sliding on a given boundary. Their effect on the development of stress
within the grains, particularly at triple grain junctions, and the increase in
axial stress along transverse boundaries are quantified. The article
demonstrates that the magnitude of the stress along the facets is
highly-dependent on the crystallographic orientations of the neighbouring
grains and the relative amount of sliding. Boundaries, transverse to the
applied load tend to carry higher normal stresses of the order of 100-180 MPa,
in cases where the neighbouring grains consist of plastically-harder
crystallographic orientations.
