Probabilistic Damage Tolerance Analysis Of Aluminum Alloy Welded Structure

With the rapid development of rail transit industry in China,the development of high-speed,comfortable,energy-saving and environment-friendly is an important issue for the development of rail transportation.As an important bearing structure of the metro vehicle body,the sleeper beam plays a very important role in the safety evaluation of the subway.Due to the non-uniform heating of the structure during the welding process,the uniformity of the material and the material parameters can be changed,and at the same time,with the production of welding residual stress,local cracks can be generated more easily than other positions.In this paper,the residual stress and material parameters of the typical welded joint are tested by the welding structure of the aluminum alloy of the car body.The damage tolerance analysis method of the welding structure based on the probability is discussed,and the method is applied to the safety evaluation of the subway sleeper beam.The main research contents of this paper are as follows:(1)The X-Ray diffraction method is adopted to test the residual stress of three forms of welding joint in the butt welding,plate welding and angle welding of the sleeper beam part of the car body,and the transverse and longitudinal residual stress distribution of the typical welded joint is obtained.(2)The crack propagation rate test is carried out on different areas of the aluminum alloy butt joint welding joint,and the crack growth rate curve of the base material,the heat affected zone and the weld zone is obtained.Using the Shapiro-Wilk hypothesis test method to analyze the dispersion of the crack propagation rate,the crack propagation rate curves of the heat-affected zone and the weld seam under different reliability were obtained by using the(?K,da/dN)and(a,N)two crack propagation rate discreteness treatment methods,respectively.(3)The influence of the stress ratio on the crack propagation of the welding seam is studied based on the test data of the crack propagation rate of the weld joint at different stress ratios,the residual stress of the welding structure is affected by the stress ratio introduction rate model,the crack propagation rate normalization model of the weld seam is established,And the crack propagation rate formula of the weld seam under different reliability is obtained.(4)The fracture toughness test data of 6005AT6 aluminum alloy butt weld is verified,and the fracture toughness of the aluminum alloy weld is verified to be in accordance with the normal distribution law,and the small sample data of the fracture toughness of the typical weld part of the vehicle body is analyzed based on the normal distribution,and the probability density function is obtained.(5)Based on the typical welding structure of the vehicle body as the research object,the probabilistic damage tolerance analysis method is discussed,including the stress of the cross section of the bolster beam and the calculation of the stress intensity factor of the crack tip,the calculation of the critical crack size of the welded joint,the residual strength and the analysis of the remaining life.Based on(?K,da/dN)and(a,N)crack propagation rate processing method,the remaining life of the sleeper beam was calculated,and the results of the two methods were found to be small.The effect of residual stress on the remaining strength and remaining life is analyzed,and when the initial crack size is 30 mm,the reliability of the sleeper beam is 90%,and the reliability of the crack propagation rate curve is 90%,and the residual life after the residual stress is considered to be reduced by about 20%.