Research On Defect Repair Principles And Mechaniced Properties Of Aluminum Alloy Joints Of High-Speed Trains

Aluminum alloy has the advantages of light weight and high strength,and is an important part of high-speed trains.The train runs at a speed of 300km/h,and the aluminum alloy welded structure has to withstand various complex loads.With the increase in the service time of trains,various defects in the structure gradually began to be exposed,and the scientific repair of the structural defects of the aluminum alloy car body needs to be solved urgently.In this paper,a combination of finite element and experiment methods is used to systematically study the optimal repair process of aluminum alloy welded structures.First,the redistribution characteristics of welding residual stress caused by defect repair are studied.Local repair will cause residual stress peaks and high stress areas.Dramatic increase.With the aid of the finite element software ABAQUS,the length,depth,and width of the repair were studied separately,and the residual stress was tested by the blind hole method to verify the accuracy of the finite element simulation.Analyzed the weld centerline,the residual stress at the weld toe,and the membrane stress and bending stress decomposed by the stress linearization.Finally,the best repair length is 15t,the repair depth is 0.25t,and the repair width is t,which is consistent with"SNL(Shallow Narrow Long)"repair principle.Under the guidance of repair principles,conduct metallographic observation and hardness testing of welds before and after repair;carry out mechanical performance tests of butt welds and fillet welds(static tensile test,fatigue performance test);carry out tests based on fatigue characteristics Parts fatigue fracture and energy spectrum analysis.The results show that the local weld structure of the aluminum alloy welded joint before and after repair is coarse,and a softened zone appears near the fusion line;the static tensile test found that the static tensile does not affect the mechanical properties of the specimen before and after the repair;the fatigue test found that under the alternating load,Defect repair reduces the fatigue life of the original welded specimen.In terms of the degree of reduction,the reduction degree of partial repair is higher than that of the overall weld.The fatigue fracture analysis of the weld found that the repaired part is the weak area of the entire test piece.In the fatigue test,the test piece first cracked from the repaired part,then expanded along the thick Ness of the plate,and finally failed and fractured.Finally,according to the BS7910-FAD diagram,the safety assessment and analysis of the butt welds and fillet welds before and after the repair are carried out.Perform quantitative characterization of flaws and cracks based on fatigue test fracture analysis.The external load of the fatigue test is used as the input of primary stress,the residual stress before and after repair is used as the input of secondary stress,and the input of fracture toughness is used to calculate the load ratio L_rand fracture ratio K_r.Input the calculation result into the FAD diagram to get the critical crack size.