In the field of simulation of railroad vehicles, there are many numerical models to estimate the interaction forces between the wheel and rail. The main advantage of these models is that they can be used together with multi-body dynamics software to calculate the motion of a vehicle in real time. However, the result of these contact models is usually post-processed to estimate wear on the profiles and some hypotheses assumed by the contact models may be inadequate for wear analysis. This is the case when considering surface roughness, which is not introduced in the numerical models and makes wear prediction imprecise. In this work an experimental method based on the measurement of ultrasonic reflection is used to solve the contact problem, together with a FASTSIM (simplified theory of rolling contact) algorithm. This technique is suitable to deal with rough surfaces and gives a better approximation of the material behaviour. Wear is estimated by means of the energy dissipation approach (T•gamma). Two different contacts are investigated, using wheel and rail profiles coming from unused and worn specimens. In order to obtain realistic results, special care is taken when locating the specimens to reproduce the same contact that appears between the wheel and the rail in the track.

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A key parameter in hydrodynamic journal bearing performance is lubricant layer thickness around the circumference of the shaft-bearing interface. In the present work, the ultrasonic amplitude, phase change and resonant dip techniques are applied to obtain circumferential film thickness profiles in a bespoke journal bearing test platform under a range of shaft-aligned, shaft-misaligned and shut-down operating conditions. Film thickness results are compared against the Raimondi-Boyd theoretical prediction model and eddy current sensor measurements. By using an on-line referencing technique, the amplitude and phase change models demonstrated high accuracy for thin films and the resonant dip technique enabled film measurements within the bearing thick film region. Thus, applying the three methods simultaneously allowed analysis of lubricant films around the bearing circumference.

The contact condition between the wheel and the rail is paramount to the lifespan, safety, and smooth operation of any rail network. The wheel/rail contact condition has been estimated, calculated, and simulated successfully for years, but accurate dynamic measurement has still not been achieved. Methods using pressure-sensitive films and controlled air flow have been employed, but both are limited. The work described in this paper has enabled, for the first time, the measurement of a dynamic wheel/rail contact patch using an array of 64 ultrasonic elements mounted in the rail. Previous work has successfully proved the effectiveness of ultrasonic reflectometry for static wheel/rail contact determination. The dynamic real-time measurement is based on previous work, but now each element of an array is individually pulsed in sequence to build up a linear measurement of the interface. These cross-sectional, line measurements are then processed and collated resulting in a two-dimensional contact patch. This approach is able to provide not only a contact patch, but more importantly, a detailed and relatively high-resolution pressure distribution plot of the contact. Predictions using finite element methods (FEM) have also been carried out for validation. Work is now underway to increase the speed of the measurement.

Rail stress levels are vital to the lifespan of rail tracks, and are responsible for the safe operation and ride comfort of train services. In particular, wheel–rail contact stress is a dominating factor affecting wear, cracking, fatigue and failure of both wheel and rail. The wheel–rail interaction problem has long been investigated, yet detailed contact information on real cases remains obscure due to the interface complexity, including the varying wheel and rail profiles and lack of effective stress characterisation methods. Ultrasound image study, as an excellent non-destructive evaluation (NDE) method, is widely used in railway systems for defect detection, stress determination and rail profile checking. Specifically, ultrasonic reflectometry has proved successful in making static machine-element contact measurements. This article introduces a novel measuring method for both short-term and long-term dynamic wheel–rail contact monitoring purposes based on ultrasonic reflectometry. The method is investigated in detail, including the study of ultrasound propagation pathways in the rail, and the optimum placement of ultrasonic elements as well as actuator–receiver combinations. The proposed monitoring technique is expected to characterise and monitor the contact behaviour of operating high-speed rail system in real-time.