Proposal for a method verifying fatigue failure of rails on curves

Abstract

In this study, as part of the development of a generic track structure design method, a method for verifying the fatigue life of rails on curves was investigated. To determine the design force for verifying the fatigue life of rails on curves, the lateral force during a vehicle run was estimated by the wheel / lateral force estimation formula by varying various parameters such as the curve radius. Taking a curve segment 800 m > R ≥ 600 m as an example, it was assumed that curves of the same extension existed for each curve radius and superelevation, and the probability frequency distribution of the variable lateral force coefficient was determined. Then, all curves on all lines laid by a certain operator were classified into three curve categories, (i) R ≥ 800 m, (ii) 800 m > R ≥ 600 m and (iii) 600 m > R. The total curve length was classified into each category, and the probability of occurrence of the lateral force was determined. When the mean and standard deviation coefficient of variation of the lateral force coefficient was calculated for the results, it was 0.25 for (i) R ≥ 800 m, 0.30 for (ii) 800 m > R ≥ 600 m and 0.35 for (iii) 600 m > R. Then, methods for estimating the bending stress at the bottom of the rail under lateral force, which is the response value, were investigated. A FEM model of both rail tracks was constructed considering vertical and horizontal bending and torsional bending, nonlinearity of the fastening systems, and lateral force on the high and low rails. The results of the analysis using this model confirmed that the bending stresses at the bottom of the rails can be estimated to be within 10 % accuracy at the bottom of the rails during vehicle passage on the service line.