Research On The Influence Of Residual Stress And Welding Method On The Fracture Performance Of Aluminum Alloy T-joints

Welding is a common joining method for aluminum alloys,widely used in industrial fields such as automotive,shipbuilding,and aerospace.During service,residual stresses from welding are an important factor affecting the structural performance of the weld,which can lead to damage and failure at the weld seam.Welding is a complex transient thermal-mechanical coupling process,and experiments cannot dynamically analyze the evolution of variables such as stress and strain fields during welding.Therefore,numerical simulation is a necessary means to study welding residual stresses and their influence on fracture performance.This study uses numerical simulation to investigate the welding process of a welded joint,analyzing the evolution of the temperature and stress fields during welding.The heat-affected zone of the weld is established using the temperature change curve.The results show that the residual stress field after welding is mainly distributed around the weld seam,with residual compressive stress away from the weld area and residual tensile stress around the weld seam.The heat-affected zone of a double-sided fillet weld is approximately 15 mm from the weld seam.Based on uniaxial tensile tests of welded joints,combined with metallographic analysis and hardness value changes induced by residual stress,the test values are compared with numerical simulation results to validate the Johnson-Cook constitutive and damage models for the 6063 aluminum alloy weld.The comparison results show that the material constitutive and damage models used in the numerical simulation are consistent with the experiment.The crystal phase structure in the weld and heat-affected zone is coarse and poorly arranged,and there is residual tensile stress at the weld,which is one of the reasons for the lower hardness value at the weld.A toughness fracture simulation model for welded joints was established by verifying damage and constitutive model parameters through experiments.Three fracture performance indicators,including load-displacement curves,equivalent plastic strain index(PI),crack initiation index(RI),and stress triaxiality(Rσ),were used to analyze the effects of residual stress on mechanical and fracture performance under different strain rates,as well as the effects of residual stress on fracture performance under different welding methods.The analysis results showed that residual stress had little influence on static mechanical performance during tensile testing and could be ignored.However,residual stress reduced overall mechanical and fracture performance during dynamic tensile testing.Among different welding methods,the fracture performance of doublesided corner welds was optimal,and the influence of residual stress was minimal.The possibility of cracking at the peak of the PI index perpendicular to the weld path was the largest for all welding methods,and the fracture performance of butt welds could be effectively improved when welded with an additional cladding plate.In order to further study the fracture behavior of welded joint,Voronoi method and crystal plastic finite element theory are used to establish the micro-tensile simulation model.The influence of residual stress on the fracture performance is analyzed at the micro-scale.From the fracture cloud diagram and stress-strain curve,it can be seen that the tough fracture process of welded joint is mainly caused by the destruction of grain boundary.The welding residual stress has no influence on the micro-overall failure mechanism of welded joint.Welding residual stress mainly results in earlier grain boundary failure and faster structural failure.