Time-variant reliability analysis of motor-hanger connecting bolts in electric trains

Due to variables in design, manufacturing and working conditions, the working loads of connecting bolts for motor hangers in electric-multiple-unit trains are uncertain. To reduce this uncertainty and improve the reliability of connecting bolts, a novel time-variant reliability analysis method has been developed. First, a parametric finite-element model of a motor hanger was established. The probability distribution of working loads for connecting bolts was then obtained by Monte Carlo simulation. Second, a one-dimensional Brownian differential equation considering the uncertainty of bolt working loads was derived based on Itō’s lemma, and expressions of the mean and variance of bolt stresses under time-variant conditions were given. The time-variant reliability model of the bolts was then constructed based on a time-variant stress–strength interference model and solved by the most-probable-point method. The results showed that the reliability calculated by this method was lower than that of the traditional method and therefore safer. It was concluded that the uncertainty of the working load has a great impact on reliability.