Wear of rails and wheels is a prevalent and costly problem in the wheel/rail system. Every year, much capital is spent on wheel/rail maintenance and renewal due to severe wear damage. Where the wheel meets the rail, non-uniform contact pressure leads to wheel wear and two types of rail wear: vertical wear on the upper head of the rail and lateral wear on the railhead side (Figure.1). The rail industry is challenged to optimize the wear of rails and wheels for improved running performance and service life of rail vehicles.
Figure 1: Schematic of wear on the rail and wheel
The wear rates of rails and wheels are dependent on the peak pressure and traction coefficient. These parameters require precise evaluation of the contact area of the rail and wheel, which is complex because of the non-uniform pressure incident on the surfaces. The contact area formed between the wheel and rail surfaces depends on their geometrical profiles, surface roughness, material properties, as well as loading conditions. The contact between rails and wheels is further complicated by surface evolution, leading to the redistribution of contact pressure and tangential traction. This means that the wear rate changes as the surface profiles of wheels and rails evolve with wear. Hence, a theoretical model is needed to perform an in-depth study of the profiles of rails and wheels to determine the contact area, contact pressure and traction distributions for prediction of the wear rate.
The objectives of the project are to investigate wear mechanisms of wheels and rails to provide an accurate model for predicting their wear behaviors and optimize the maintenance schedule. The implementation scheme of the project is illustrated in Figure.2.
The developed technology includes:
- Develop a multibody dynamic model to predict contact force between wheels and rails
- Determine the wear coefficients of wheels and rails under various working conditions through wear testing.
- Develop a wear model to predict profile evolution for wheels and rails from the wear testing results.
Wear testing of wheels and rails was systematically conducted by considering the influences of velocities and loads (Figure.3). The wear results were used to construct a database for the wear performance of wheels and rails to provide detailed material information for the modeling.
A comprehensive platform has been developed to analyze and predict the wear of wheels and rails. The developed methodology in this project has systematically considered various factors that are experienced in SMRT system, such as dynamic friction, vehicle configuration, and contact geometry. The wheel and rail profile evolution due to wear has been successfully implemented in the platform, as shown in Figure.4, in which the wear testing results have been used as inputs in the model. Based on our platform, a design strategy has been developed for profiles of wheels to increase their wear resistance.
Moreover, surface treatment technique has been developed to enhance wear resistance of wheels and rails with considerations on the evolution of their contact interface and contact stress.