Development of numerical model to investigate the process mechanics of eccentric square pin during friction stir welding

The tool pin feature is a key factor for driving the weld quality and material flow characteristics during friction stir welding (FSW). A thermomechanical coupled Eulerian-Lagrangian (CEL) model is developed to simulate the influence of tool pin eccentricity (0.0, 0.1, and 0.2 mm) on the variation of mechanical properties, material flow, temperature, and forces. The Eulerian volume fraction (EVF) technique has been used for defect identification, and the model is validated with experimentally observed defects, peak temperature, and forces. Results show enhanced mechanical and thermal characteristics with increased pin eccentricity and tool tilt angle. The eccentric pin resulted in an enhanced effective pin geometry, resulting in higher swept volume, i.e., leading to improved strength and plastic deformation with a higher rotational path of the material. Widening of the stir zone is observed with an increase in pin eccentricity from 0.0 to 0.2 mm. The highest weld efficiency of 86 % is obtained for $2^o$ tilt and 0.2 mm pin eccentricity with a stirred zone peak temperature of 439 °C and 9.4 effective strain. The material flow is studied using tracer material to understand the extent of material flow behavior with pin eccentricity. Variation in temperature, heat flux, strain, and material velocity is studied for different angular motions of the tool pin.