Simulation of friction stir welding in butt welds of grade 5 titanium alloy and measurement of heat distribution

Abstract

Residual stresses are generally referred to as stresses that exist in parts without applying external force and loading, and all of the components of these stresses have reached equilibrium with each other in different directions in the part. One of the major problems in welding is the creation of residual stress and distortion due to local heating. As a result of intense heat concentration in the welding area, the areas near the welding experience several thermal cycles. These thermal cycles cause non-uniform heating and cooling of the material and, as a result, create heterogeneous deformations and residual stresses in the part. Friction stir welding (FSW) is one of the widely used welding methods in various industries, such as aerospace. The measurement of heat distribution in the FSW process is an important challenge. In this welding method, the issue of heat transfer, fluid and dynamic equations resulting from tool movement, as well as the cooling of the part up to the temperature of phase transformation in welded parts, play a significant role in accurately predicting the residual stresses caused during welding. In this research study, the regime of cooling and heating of the material, and as a result, the residual stress magnitude during the FSW process, was simulated by using the equations related to heat transfer and temperature-dependent properties of the material. To do the simulation, ABAQUS software was used, accompanied by the DFLUX subroutine. After validating the simulation results by means of experimental welding and tests, the effect of temperature changes on the creation of residual stress resulting from heating and cooling cycles during welding was examined.