Thermomechanical analysis of friction stir welding using a new velocity-based model for tool-workpiece interaction

The friction stir spot welding test was designed to measure the coefficient of friction on the tool-workpiece interface under different tool rotational speeds. The boundary velocity of the workpiece material was calculated based on the stress state of the material on the interface. An integrated computational fluid dynamics (CFD) model of friction stir welding (FSW) was established based on the coefficient of friction and boundary velocity of matrix to simulate heat and mass transfer. A more realistic boundary velocity distribution was acquired. A method was introduced to predict strain along a streamline by integrating the strain rate along with the streamline’s reverse. The nephogram of strain on the transverse cross-section of weldment displays that strain at the advancing side (AS) is more significant than that at the retreating side (RS), and strain increases as the distance from the shoulder surface decreases. Strain in some regions can be tremendous if the material flows through the rotation flow zone. Wall heat flux on the tool-workpiece interface at RS is more significant than AS. The maximum temperature was observed at the front part of RS. The model is validated since the predicted temperature profile agrees well with corresponding experimental results.