Unified probabilistic approach for fatigue assessment of rolling stock bearing structures

Abstract

Introduction. The probabilistic approach allows to obtain a fatigue assessment considering loading history and characteristics of the fatigue resistance spread and is widely used to calculate the service life of bearing structures of the undercarriage. The approach is based on the application of linear damage summation rule and the transition to the loading limit block. However, approach is presented differently in regulatory documents for different types of rolling stock. The objective of the study is to demonstrate the possibility of unification of probabilistic regulatory methods used for fatigue assessment of different types of rolling stock.
Materials and methods. The regulatory documents data on the strength and dynamic qualities assessment of locomotivehauled cars, EMU cars and locomotives were analysed.
Results. The methods for fatigue assessment under irregular loading are considered, using the concept of equivalent stress and the concept of transition to the loading limit block. A comparison of methods for the values of fatigue safety factors with identical values of the coefficients of variation of the fatigue limit and maximum stress in the block is performed. It is shown that with statistically reliable data on loading and fatigue limit, the smallest fatigue safety factor is included in regulatory documents for the strength assessment of locomotive cars. The author proposes to use an approach in which stress amplitudes are normalised by the fatigue limit value. Conservatism of the deterministic approach is shown in comparison with the probabilistic one.
Discussion and conclusion. The proposed approach allows simplifying the calculations of durability of the rolling stock bearing structures and solving several types of problems: assessing the durability corresponding to a given failure probability, calculating the failure probability at a given durability, assessing the values of the fatigue safety factor. This allows to consider it as a unified approach for different types of rolling stock.