Residual State Prediction Method Of Large Size FSW Weldments Based On Stress Mapping

In recent years,Friction stir welding(FSW),as a new solid-state bonding technology,has been widely used in the welding of light alloys such as aluminum and magnesium.Rail transit industry is the top priority in China’s infrastructure construction.Welding quality and welding efficiency are important indicators of vehicle production.Therefore,FSW has been gradually promoted to the production and manufacturing of rail vehicles.FSW welded components rarely appear welding defects,but the residual state of welded parts after welding will affect the service life of components and the overall assembly accuracy.Therefore,the research on the residual state after friction stir welding has important scientific significance and engineering application value.Test measurement is one of the important means to study the residual state of welding,but the test will cost a lot of money and manpower,so the numerical simulation has become an important means to study the residual state of welding.Thermoelastoplastic method,as a numerical simulation method of post-welding residual state,is widely accepted by scholars at home and abroad.It has incomparable advantages,but it has low computational efficiency and time consumption.Therefore,based on the finite element analysis software ABAQUS,this paper developed two methods for predicting the post-welding deformation of friction stir welding,and carried out FSW post-welding deformation prediction for the subway end-wall stiffened plate structure.The integral model and the local model of the thin plate were established.The numerical simulation of the integral model and the local model FSW welding process was carried out by the sequential thermodynamic coupling method,and the thermal field,stress field and deformation field were analyzed.The residual deformation results of the overall model were compared with the experimental results in the literature to verify the effectiveness of the numerical model.On this basis,the influence of size effect on the stress state before fixture release is analyzed,and the feasibility of "local-global" stress mapping idea is verified.Based on the existing basic idea of temperature equivalent load method,an improved temperature equivalent load method considering the effect of stress gradient was proposed,and the nature of deformation was effectively identified.Meanwhile,the effect of zonal equivalent mapping method on welding deformation prediction was discussed.Based on the partition equivalent mapping method,the temperature equivalent load method is applied to predict the post-welding deformation of the whole model.The prediction results were compared with the deformation data measured by experiments in the literature,and the validity of the prediction method was verified.In this paper,a stress mapping method is developed to predict the welding deformation by averaging the regional stresses of the local model and mapping them to the corresponding region of the global model.The deformation prediction results are in good agreement with the experimental measured deformation data in the literature,which verifies the effectiveness of the stress mapping method presented in this paper.The stress mapping method and temperature equivalent load method are compared and analyzed.The temperature equivalent load method is used to predict the welding deformation of the subway end wall stiffened plate structure.Based on the local model,the prediction results of the temperature equivalent load method are compared with those of the thermoelastoplastic method,and the effectiveness of the temperature equivalent load method in predicting the post-welding deformation of the stiffened plate structure is verified.On this basis,the shell-solid coupling method was used to establish the overall model of the subway end wall stiffened plate structure,and the temperature equivalent load method was used to predict the post-welding deformation.In the process of implementing the method,the birth and death element method is used to simulate the actual welding process.The welding sequence optimization of the subway end wall stiffened plate structure was studied and the optimal welding sequence was determined.In this paper,the temperature equivalent load method and the stress mapping method are studied in theory and calculation methods,and the two methods are used to successfully predict the post-welding deformation of friction stir welded plates and stiffened plates,which provides a theoretical basis and reference for the prediction and control of welding deformation of large size structures.