Numerical analysis of material flow in the probeless friction stir spot welding based on Coupled Eulerian-Lagrangian approach

AA2198 joints were produced using the probeless friction stir spot welding (P-FSSW). Numerical modeling of the process based on the Coupled Eulerian-Lagrangian technique was developed to investigate the material flow. The modeling and experimental observations provide a consistent interpretation of the circumferential material flow which has some inward radial flow at the top surface. As the welding process advances, the flow is directed downwards, producing a spiral contracting pattern. The simulation results show that the hook defect is formed as the material in the bottom sheet is squeezed upwards in a symmetrical fashion with respect to the centerline, matching well with the experimental results.