Stress Analysis And Fatigue Assessment Of Spot Welded Structures Of Railway Vehicles

Stainless steel materials are widely used in rail vehicles because of their own light weight,strong corrosion resistance,no need for coating on the surface and low maintenance cost.The stainless steel car body of the rail vehicle mainly uses the resistance spot welding process.The whole car body has about 30,000 to 40,000 spot welds.During the running of the vehicle,these spot welds will be subjected to various alternating loads,which are prone to fatigue damage.In order to ensure the safety and stability of the car body during service,it is very necessary to analyze the fatigue characteristics and life of the car body spot welds.In this paper,based on the online elastic fracture mechanics,the spot welds is regarded as a rigid body contained in the base metal plate,and the load of the lap-shear specimens is decomposed into several different symmetrical and anti-symmetric single loads.Based on the Airy stress function and the Kirchhoff plate theory,combined with the boundary conditions of the finite plates,the stress of the spot welds under each different load condition is obtained.The stress distribution around the spot welds of the lap-shear specimens is obtained by superposition.Then the stress intensity factors of the specimens were studied by Radaj structural stress method,finite element method and Rupp structural stress method.Based on the Radaj structural stress method,the stress intensity factors under different single loads are obtained by using the infinite strip model and J integral.The load of the specimens is decomposed into several different single loads,and the stress intensity factors of the specimens are obtained.Based on the finite element method,the finite element model of the welded joint structure is established by using the solid element of HyperMesh software.The post-processing module of ANSYS software is used to define the crack path and calculate the stress intensity factor of the welded joint.Based on Rupp structural stress method,shell element and beam element are used to simulate the finite element model of the spot welds in lap-shear specimens.The mechanical parameters of the welded joint beam element are calculated and extracted by ANSYS software,and then the stress intensity factor of the welded joint is obtained.Comparing and analyzing the calculation results of the three methods,it can be seen that the accuracy of the calculation results of mode I stress intensity factor obtained by the three methods meets the engineering requirements.However,the Rupp structural stress method is simple and suitable for the stainless steel body of rail vehicles with tens of thousands of spot welds.Finally,based on the American ASME-2007 standard,the fatigue life of stainless steel body spot welds of rail vehicles containing tens of thousands of spot welds was evaluated.The shell element and the beam element are used to simulate the solder joint structure,and a simple and effective finite element model of the stainless steel car body is established.The stainless steel spot welding car is loaded according to the fatigue condition specified in the BS EN12663-2010 standard,and the principal stress cloud diagram of the vehicle body fatigue condition is obtained by using the ANSYS finite element calculation software.The joints with large principal stresses under fatigue conditions were selected.The equivalent structural stress of the joints was obtained by FE-WELD software.The fatigue life of the joints was evaluated based on the Paris fracture mechanics formula.The results show that the cumulative fatigue damage of the spot welds is less than 1,which meets the service requirements of the vehicle body.The research work of this thesis provides a scientific basis for improving the quality of stainless steel body welding points of rail vehicles,and has important theoretical research and engineering application significance.