Dynamic reliability analysis for fatigue strength of aluminum alloy welded bodies for EMU

LU Yaohui; JIANG Mingjun; WANG Qiushi; ZHANG Yadong; XIANYU Yueheng; ZHU Shengchang

doi:10.11860/j.issn.1673-0291.20240096

Abstract：The welded seams of the rolling stock body are subjected to complex multi-axis random loads during service.To address the issue of dynamic fatigue reliability assessment,a dynamic stress-strength interference model is established for precise calculation in this paper.First,the vertical and longitudinal load spectra for the intermediate car body are compiled,and an agent model method is em-ployed to transform the multi-axis stochastic loads acting on the car body into dynamic structural stresses at the weld seams.Second,the equivalent structural stress range for the welded joints of the car body is adjusted using the rainflow counting method,and the stress probability distribution is ob-tained by fitting a two-parameter Weibull distribution.Finally,the strength data are derived from the Stress-Number of cycles(main S-N)curve of aluminum alloy welded joints,and a dynamic stress-strength interference model is established by integrating a damage-based strength degradation model with the stress probability distribution function and the probability density function.This model is used to study the fatigue strength reliability of the dynamically changing car body.The results indicate that the fatigue strength reliability of the critical parts of the car body is initially high but gradually decreases as the operating mileage increases.Over 14 million kilometers of service,the fatigue strength reliabil-ity of the lap weld,located near the vertical load input position of the underframe,decreases the most,reaching 0.116 5.The failure rate of the critical points of the car body first decreases and then increases with the increase in operating mileage,exhibiting the characteristics of the bathtub curve,which in-cludes an early failure period followed by a wear-out failure period.The polynomial fitting method for calculating the dynamic stresses of large-scale vehicle body structures proves to be both feasible and ef-ficient.This approach can serve as a reference for the operation,maintenance,and safety and reliabil-ity assessment of the car body.