Numerical Computation Of Welding Residual Stress And Analysis Of Influence On Strength Reliability Of Aluminum Alloy Carbody

Compared with other modes of transportation,high-speed trains have the advantages of large passenger capacity,comfortable safety,freedom from climate conditions,energy conservation and environmental protection,and promotion of regional economic development,and are therefore widely used in China.As the core component of the high-speed train system,the carbody is assembled by using aluminum alloy extruded profiles in order to meet the lightweight requirements.Welding is the most basic and important connection method in the production of high-speed trains.Welding quality directly affects the bearing capacity and service life of the car body.The aluminum alloy material has a rapid heat transfer and a large linear expansion coefficient.It is prone to produce welding defects such as blowholes and slag inclusions in the welding process,and it is inevitable to generate large welding residual stress.As the speed of trains continues to increase,the forms of load that the carbody bears are more complex.The residual stress caused by welding not only reduces the strength performance of the car body,but also affects the stress caused by the external load the carbody bears,which poses a threat to the structural strength reliability of the carbody.This paper takes the middle carbody of a high-speed train body as the research object,studies the calculation method of the residual stress of the high-speed train body,and evaluates the structural strength of the car body under the influence of residual stress,and provides reference for vehicle body design and manufacture.Firstly,a dual-weld butt joint model is established for the MIG automatic welding used in the carbody manufacturing process.The welding conditions and the related material parameters were determined.The internal heat generation rate and the life-and-death element method were used to realize the heat source movement and the weld filling process.The time step and constrained method and the nonlinear option are set.The indirect heat-engine coupling method is used to simulate the welding temperature field and residual stress field.The analysis results show that the middle section longitudinal residual stress shows two peaks at the heat affected zone,which are 250 MPa and 259 MPa,the transverse residual stress is far less than the longitudinal residual stress.The welding test is conducted and the obtained data were compared with the numerical simulation results.The data agreed well with each other.Then according to the joint size used in the car body to establish the corresponding geometric model and finite element model,the numerical simulation method is used to calculate the welding residual stress distribution of each joint,the board shell model of the typical joint body is established,and each joint entity is calculated through the inherent strain method.The residual stress field of the plate and shell model is compared with the results of the thermo-elastic plastic method.The residual stress curves obtained under the three conditions have the same trend,and the error meets the accuracy requirement of the actual engineering calculation.Based on this,a finite element model of the car body plate shell is established,and the inherent strain of each type of joint plate shell model is applied to the car body to obtain a car body model with residual stress,and the residual stress distribution of the car body is mainly concentrated in the weld seam.In and near it,the stress value is between 60~80MPa.Finally,the current three vehicle body design standards in the railway industry are compared,the static and fatigue strength conditions of the vehicle body are determined,and the body load and restraint modes are simplified according to the actual operation conditions.The reliability safety coefficient method and the Goodman curve are used to convert the multiaxial stress according to the fourth strength theory and the principle of maximum principal stress.Calculate the static strength and fatigue strength of the vehicle body with or without residual stress.The results show that the static strength and fatigue strength of the vehicle body meet the design requirements in both cases.Residual stress affects the position where the maximum stress occurs in static strength conditions and significantly affects the fatigue strength of the carbody,especially the weld line.