Underwater friction stir welding of PC: Experimental study and thermo-mechanical modelling

Abstract

In underwater friction stir welding (UFSW), the thermal conditions between the tool and the plasticized polymeric materials and the relation between glass transition temperatures remain unclear. In this work, a developed coupled 3D thermo-chemical-mechanical numerical model was applied to simulate the UFSW process of polymeric materials. A computational fluid dynamic analysis was conducted for the evolution of the pressure, viscosity and temperatures properties on submerged situation. The numerical model is able to prediction of shrinkage percentage and formation of air gap on the joint stir zone (SZ) by evolution of the mixed slipping/sticking contact conditions at tool/workpiece interface. The simulation results were validated with experimental data on polycarbonate (PC) polymer. It was found that, higher cooling capability of water leads to lower heat concentration on the joint line and consequently, during traverse movement of UFSW tool, the materials viscosity in the leading edge was higher than FSW case. Higher viscosity materials caused the ∼6.8 % lower heat generation and smaller SZ at UFSWed sample. It is shown that the material stirring in FSW joint is higher than UFSW that leads the higher shrinkage percentage and air gap formation. On the other hand, the immersing situation caused the water droplet diffuse into SZ of the UFSW sample. The crystallinity and chemical structural changes of PC in submerged situations were lower than conventional FSW joint, and consequently, the tensile properties and hardness of the welded sample improves in UFSW joint.