Numerical study of mesoscale surface roughening in aluminum polycrystals under tension

A 3D numerical analysis of mesoscale surface roughening in a polycrystalline aluminum alloy under uniaxial tension has been performed. Three-dimensional microstructural models with equiaxial and extended grains inherent in cold rolling have been developed and used in calculations. Crystallographic anisotropy is not described in an explicit form by means of, say, a well-known crystal plasticity model. Instead, the elastic-plastic properties of individual grains are varied within 10% and in so doing the mechanical anisotropy due to the grain shape is accounted for. A combined effect of microstructure and loading and boundary conditions is investigated. Pronounced surface roughness of equiaxial grain structure and of a textured material loaded at the right angle to the rolling direction is observed in comparison with extended grain structure loaded along the rolling direction where the surface relief is fairly smooth. Computational results suggest that grain structure is responsible for the formation of a free surface relief during uniaxial loading. Microscale normal and shear stresses associated with the direction perpendicular to the free surface develop in the bulk of the material and, acting from the inside, give rise to surface ridges and valleys.