Probing finite element modelling of defects in friction stir welding by tailoring mass scaling factor

Friction stir welding (FSW), a solid-state welding process primarily used to join the low melting point materials, often encounters surface and subsurface defects. Modelling surface texture and internal volumetric defects in the FSW process using any numerical method is computationally expensive. The analysis of thermo-mechanical behavior of the FSW process using coupled Eulerian-Lagrangian (CEL) method is sensitive to mass scaling factor (MSF). Tailoring this factor for a computationally efficient model is a promising approach to predict defect in FSW process. The influence of MSF on the computational framework of the CEL finite element method (FEM) in the context of defect formation for two different types of materials (difference in densities) is addressed in the present work. The progress of different energies associated with the CEL approach is indicative of the solution availability by the application of MSF. The variation of these energies is significantly high in FSW process when encountering a defect and dictates the optimum conditions of MSF. An optimum range of MSF is deliberated on account of an efficiently model of FSW process. The simulated surface and subsurface defects, and the discrete temperature data are compared with experimental observation. The maximum difference between the predicted and experimentally measured tunnel defect is ∼ 0.75 mm, whereas the predicted temperature is within 5% of experimental result. It establishes the reliability of the developed numerical model and directs to trigger the model parameters for minimizing the computational time by tailoring the MSF. The optimum range of MSF between 106 and 107 strikes a balance between the result accuracy and computational feasibility for welding of AZ31B. Here, the distribution of strain and strain rate is representative of predicting the defect formation, such as, void, no material zone, crack, surface texture etc. The strain rate is almost double on the retreating side (RS) compared to advancing side (AS) due to the presence of the tunnel defect on AS.