Research On Fatigue Of Laser-arc Hybrid Welding Stainless Steel Subway Bolster Based On Master S-N Curve Method

China's rail transit has developed rapidly and has achieved remarkable results.As an important part of rail transit,metro vehicles have also been vigorously promoted by more developed cities.Stainless steel is widely used as an excellent corrosion-resistant high-strength steel in subway manufacturing.Welding is the main manufacturing method of subway vehicles,and the metal welding structure faces a serious problem-fatigue damage.Therefore,the fatigue life assessment method and theory of stainless steel materials for subway should be carefully studied,which has important guiding significance for the design and safe use of stainless steel structures on the subway.Firstly,this paper has analyzed the research status of fatigue life assessment theory at home and abroad,and compared the advantages and disadvantages of nominal stress method,hot spot stress method and structural stress method,and has carried out indepth analysis on the main S-N curve method based on structural stress.The finite model of different mesh sizes is established to calculate the structural stress distribution at the weld toe of the T-joint and calculated stress distribution of the finite element analysis.It is proved that the meshing insensitivity of the structural stress method is insensitive.Then the test welding plate of SUS301L-HT was welded and the fatigue test was carried out.And the fatigue test data was fitted with the SN curve based on the nominal stress method,and the SN curve was fitted and analyzed.There is a significant linear relationship between stress level and fatigue cycle times.Secondly,the six component files of the residual stress distribution field are output by Sysweld software,and the complete residual stress distribution field file is synthesized by Matlab program.Then it is imported into Abaqus to calculate the fatigue life based on the nominal stress method under the residual stress superposition state,and then the fatigue life calculation of the test welding plate is carried out by using themaster S-N curve method.Comparing the nominal stress method with the main S-N curve method for fatigue life prediction,it is found that the master S-N curve has better stability in the face of the influence of residual stress on fatigue.Thirdly,the finite element analysis of the structure of body bolsters has been carried out,and the structure is meshed using the solid element.The static stress analysis under the load combination of 16 kinds of loads based on EN 12663 standard,with 6 key welds as the focus,the structural stresses and structural stress variation ranges of each weld were calculated by the master SN curve method.Finally,the fatigue life of the evaluation points on each weld is calculated.The fatigue life prediction results show that each weld has reached 10 million cycles.Finally,in order to verify the accuracy of the fatigue life prediction of the master S-N curve method,a full-scale fatigue test was carried out on the bolster structure,and the test results were consistent with the prediction results of the master S-N curve method.