Stress-accurate FE framework for the numerical simulation of the FSW process
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In this work the current developments on the numerical simulation of the Friction Stir Welding (FSW) process are presented. A fully coupled thermo-mechanical framework has been tailored to account for the heat flux generated by the plastic dissipation in the stir-zone (rigid-visco-plastic constitutive model) as well as the frictional dissipation at the contact interface between the pin-tool shoulder and the work-piece (Enhanced Norton frictional contact model) [1]. Combining the use of the 3-field (u/e/p) FE technology in the Thermo-Mechanical Affected Zone and the classical mixed u/p formulation elsewhere allows for the optimal balance between the required stress accuracy in the proximity of the process zone and an affordable computational cost. An error-estimator switch to the 3-field formulation when high strain-rate gradients are detected enforcing the continuity of the stress field [2,3]. The Variational Multi Scale (VMS) method is used to circumvent the LBB stability condition allowing the use of linear piece-wise interpolations for displacement, Strain-rate and pressure fields, respectively. A fully parallel FE implementation (ready for distributed memory machines) combined with an adaptive mesh refinement strategy allows for the analysis of FSW tools of industrial interest. The meshing consists of a Cartesian voxelization and an octree-type local refinement (h-type adaptivity) to preserve the geometrical details of the pin-tools as well as to capture the high temperature gradients in the HAZ. The proposed model is calibrated and validated with the experimental measurements carried out by HYDRO.
