A fully three-dimensional two-scale boundary element approach to degradation and failure in
polycrystalline materials is proposed. The formulation involves the engineering component level (macroscale)
and the material grain scale (micro-scale). The damage-induced local softening at the macroscale is
modelled employing an initial stress approach. The microscopic degradation processes are explicitly
modelled by associating Representative Volume Elements (RVEs) to relevant points of the macro
continuum and employing a three-dimensional grain-boundary formulation to simulate intergranular
degradation and failure in the microstructural Voronoi-type morphology through cohesive-frictional contact
laws. The scales coupling is achieved downscaling macro-strains as periodic boundary conditions for the
RVE, while overall macro-stresses are obtained via volume averages of the micro-stress field. The
comparison between effective macro-stresses for the damaged and undamaged RVE allows to define a
macroscopic measure of material degradation. Some attention is devoted to avoiding pathological damage
localization at the macro-scale. The multiscale processing algorithm is described and some preliminary
results are illustrated