Research On Fatigue Life Of Metro Welded Frame Based On Effective Notch Stress

The increasing use frequency and increasingly complex operating conditions of metro vehicles put forward high requirements for the operation safety of its key structural parts.It is necessary to carry out anti fatigue design of bogie frame according to the requirements of full-life service.Fatigue failure may occur at the weld toe and weld root of the welded joint of the frame in the actual operation of the vehicle.Only by selecting a reasonable fatigue evaluation method can the fatigue life be predicted accurately,comprehensively,and reliably.In this paper,taking the metro frame as the research object,based on the effective notch stress,aiming at the fatigue failure of the weld toe and weld root of the frame fatigue control part,the fatigue life of the frame is studied.The main contents are as follows:(1)Fatigue tests are carried out on the cross-bearing corner joint,T-shaped nonbearing corner joint and butt joint of steel materials for bogie,the nominal stress S-N curve is fitted,compared with the S-N curve parameters recommended by IIW,and the differences and causes are analyzed.(2)The formula method and numerical method are used to calculate the effective notch stress concentration factor at the weld toe and weld root of three types of joints in fatigue test samples.Analyze the plate thickness t,leg length l and weld angle θ、 The influence of weld throat depth a,root gap 2c and other weld joint parameters on the effective notch stress concentration factor.(3)The effective notch stress concentration factor at the weld toe and root of class A,B and C joints calculated by numerical method is combined with the nominal stress fatigue test data to obtain the effective notch stress S-N curve which can be used in the fatigue evaluation of metro frame.(4)The pipe-plate joint model of the fatigue control part of the frame is established,and the effective notch stress concentration factor is calculated by numerical method.The normal distribution parameters of nominal stress and effective notch stress are obtained by combining the equivalent nominal stress of the transverse and side beam connection obtained in the long-term dynamic stress tracking test.According to the stress strength interference relationship of the nominal stress method and the effective notch stress method,the fatigue failure of the connection of the transverse and side beams of the frame is predicted,and the advantages and disadvantages of the two methods are compared.(5)Establish the overall finite element model of metro frame and the effective notch sub model of frame fatigue control part,calculate the cumulative damage and equivalent stress at the weld toe and weld root of the sub model,and analyze the parts prone to fatigue failure according to the results.The weld models with different leg lengths l are established to study the effect of weld size on the effective notch fatigue life to improve the design life and avoid the fatigue failure at the weld root.80 Figures,14 Tables,115 References...