A mesomechanical analysis of the stress-strain localisation in friction stir welds of polycrystalline aluminium alloys

A numerical analysis is presented of the microstructural effects on the deformation and fracture of friction stir welds in aluminium alloys. A dynamic boundary-value problem in a plane strain formulation is solved numerically by the finite-difference method. Experimental polycrystalline microstructures inherent in different weld zones-base material, weld nugget, and thermo-mechanically affected zones-were accounted for explicitly in the calculations. To simulate the mechanical response of individual grains, use was made of an elastic-plastic formulation of the problem accounting for isotropic strain hardening, including the Hall-Petch effect, and of a fracture model allowing for crack initiation and growth in the regions of maximum equivalent plastic strains. Plastic strain and fracture localisation is shown to depend on the strength of welded materials.