Research On The Method Of Probabilistic Damage Tolerance Analysis For EMU Carbody

The development of society and the progress of science and technology promote the development of modern transportation industry rapidly.Through the introduction of foreign advanced technology,joint design and manufacture,to the present independent research and development,China has made remarkable achievements in the development of high-speed railway.Now,China’s high-speed EMU(Electric Multiple Unit)technology has ranked among the world.As the main load-bearing structure of high-speed EMU,the carbody is especially important in the structural design of carbody.Due to the comprehensive effects of processing technology,welding technology,service load and service environment,cracks and other damage will occur in the part of the car body after a long time service.This paper mainly aims at carbody of the first carriage of EMU.The random factors in probabilistic damage tolerance analysis and the calculation method of stress intensity factor at the crack tip are studied.The main contents of this paper include:(1)According to the structural features of the first car body of the high-speed EMU,the HyperMesh software is used to establish the finite element model of the car body.Based on the analysis of the state of force in the actual operation of the vehicle,6 kinds of typical working conditions are set up referring to Japan’s "JIS E7106:2006";for each working condition,the simulation calculation is carried out to check the strength and rigidity of the car body to determine the stress state of the car body in the vulnerable parts.(2)Taking into account the dispersion of material properties in the analysis of the probability damage tolerance,the research on the fracture toughness and fatigue crack growth rate of the car body material is carried out.SPSS software is used to draw normal P-P graph and normal Q-Q graph of fracture toughness of Lc4 aluminum alloy and 30CrMnSiNi2A two materials in the literature,and the normality test is conducted by W test.According to the statistical analysis of the fracture toughness test data of the vehicle body material,the probability density function is determined.According to the assumption that the crack propagation rate obeys the logarithm normal distribution under the same magnitude of stress intensity factor,the processing method of the crack propagation rate test data is proposed and the material parameters C and m in the crack growth rate formula under different reliability requirements are obtained.(3)According to the characteristics of the finite element model of car body,the J integral method is applied to calculate the stress intensity factor of the crack tip of the car body.Based on the complicated stress state and the efficiency of simulation,the selection principle of element type in the modeling process is put forward.The element coupling problem in the modeling process is discussed,and the accuracy of the simulation is checked.(4)The probabilistic damage tolerance analysis method of the vehicle body is discussed,including the calculation of critical crack size,the analysis of residual strength and the calculation of residual life.Based on the proposed method,the crack of the vehicle’ draft sill wing plate is analyzed,and the critical crack size,safety residual strength and residual life of the draft sill under different reliability are obtained respectively.