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Numerical analyses of the roller-raceway contact have been carried out in a spherical roller bearing using frictional contact models of different complexity. The models used in the study include an implementation of Kalker's exact contact theory named CECT (Conformal Exact Contact Theory) and detailed Finite Element models. The adequacy of the more simplified contact solutions is assessed by contrasting them with the solutions obtained with themore comprehensive models. Additionally, the use of the exact contact theory, well known in the wheel-rail application, is demonstrated in contact mechanics analyses in rolling bearings, describing relevant details of its implementation for this application. Situations with different normal loads and friction levels have been analysed, and two distinct steady equilibrium configurations of the roller have been identified. [ABSTRACT FROM AUTHOR]

Field application of friction modifiers on the top of rail has been shown to effectively curb squeal and reduce lateral forces, but performance can be variable, according to other relevant research. Up to now, most investigations of friction modifiers were conducted in the field, where it is difficult to control or measure important parameters such as angle of attack, rolling speed, adhesion ratio etc. In the present investigation, the effect of different friction modifiers on the occurrence of squeal was investigated on a rolling contact two disk test rig. In particular, friction-creep curves and squeal sound pressure levels were measured under different rolling speeds and friction modifiers. The results show friction modifiers can eliminate or reduce the negative slope of friction-creep curves, but squeal noise still exists. Theoretical modelling of instantaneous creep behaviours reveals a possible reason why wheel squeal still exists after the application of friction modifiers. [ABSTRACT FROM AUTHOR]

Abstract: Curve squeal is the result of the lateral force in rolling contact of rail and wheels along curves. Recently, field measurements of wheel squeal occurrences at a site in Australia showed an increasing possibility for a squeal event to occur as the relative humidity increases. To verify these results, a new method to measure the lateral and normal force simultaneously was developed on a test rig, so as to determine the friction-creep curves. To investigate the effect of relative humidity on squeal and friction creep curves, the relative humidity inside the acoustic enclosure of test rig was adjusted under controlled conditions of 50%, 70% and 90%. The test rig results show that the lateral adhesion ratio decreases slightly with the increase of relative humidity and that squeal is more likely in high relative humidity. The modelling analysis shows that the critical creepage decreases with the increase of the relative humidity, which means negative damping occurs for lower angle of attack. [Copyright &y& Elsevier]

Friction modifiers have been shown to be effective in reducing wheel squeal noise but not reliable in eliminating the phenomenon. To investigate this, wheel squeal noise under water-based friction modifiers is predicted using a mathematical model taking into account assumed instantaneous traction-creep behaviour. The instantaneous lateral creep curves are determined from quasistatic measurements under water-based friction modified conditions and used to obtain analytical predictions of wheel squeal noise levels that are verified numerically and experimentally based on a two disk testrig. Similar levels of squeal are obtained in both dry and water-based friction modified conditions at higher speeds despite the measured lateral creep curve not showing 'falling friction'. For low speed, the water-based friction modification is shown to be successful in eliminating squeal except for very high angles of attack where noise levels are still greatly reduced. Subsequently, the efficient modelling is used to identify what modifications to the creep curve provide the best squeal noise reduction and elimination capabilities. • Squeal noise trends under water-based friction modifiers are analytically predicted and verified experimentally. • Squeal noise was not eliminated by friction modifiers in some cases at higher speeds and angles of attack. • Generalised optimal friction modified creep curves are predicted and verified numerically to control wheel squeal noise. • Squeal noise can be substantially reduced while still maintaining moderate friction levels by increasing the critical creep. [ABSTRACT FROM AUTHOR]

Abstract: Rolling contact fatigue cracks in railway track called squats are studied in this paper. In the first part, the effects of an elastic foundation (sleepers and the ballast) on stress intensity factors obtained at a crack tip are studied. A simplified finite element model (FEM) and an extended finite element model (XFEM) were created to investigate these effects, the XFEM model being limited in geometrical size, but more able to model crack growth. Both FEM and XFEM confirmed that an elastic foundation leads to an additional bending stress which increases the crack growth rate significantly. Field results also authenticate that squat form cracks appear on timber sleepers more commonly than on concrete ones. These results indicate that considering these bending stresses in a FE model, is important to achieve a more realistic model of squat development. In the second part, a short crack of 250μm length is simulated to investigate how variations of traction ratio (TR), friction coefficient between the crack faces (FC) and the crack angle affect SIFs when the rail is mounted on an elastic foundation. Simulations show that a crack on a rail laid on elastic foundation (clips, sleepers and ballast) can lead to significantly higher SIFs in many conditions and consequently raises crack growth rate. This indicates that foundation stiffness is as important as water entrapment and friction coefficient between the crack faces. [Copyright &y& Elsevier]

A rolling contact two disk test rig is used to measure the lateral adhesion ratio under dry and wet conditions, and the results show that after the application of water the lateral adhesion ratio decreases. This effect is especially evident for low speed at large angle of attack, and the reduction rate is almost up to 50%. In contrast, the effect of water application on the lateral adhesion ratio at high speed is almost negligible. In this research, the effect of rolling speed on the lateral adhesion ratio under dry and wet conditions are also investigated. It is found that the lateral adhesion ratio decreases with rolling speed under dry conditions; while after the application of water, the measured results show an opposite trend. Furthermore, a model of wheel/rail contact mechanics is developed based on previous models and experimental measurements. Using this model, the simulated friction creep curves shift down with the increase of rolling speed. In comparison with previous mathematicla models, the correlations of this theoretical model with measured lateral adhesion ratios at various rolling speeds are much improved. Hereby, the authors would like to highlight the following innovations and contributions of this paper. ● The lateral adhesion ratios at various yaw angles and rolling speed are measured under dry and wet condition, and the effect of water application is investigated. ● The effect of rolling speed on lateral adhesion ratio under wet condition is investigated and illustrated, and the effects of low speed and high speed are compared. ● A theoretical model for wheel/rail contact in the lateral direction based on the contact theory of Kalker is developed and its correlation with experimental measurements is much improved. [ABSTRACT FROM AUTHOR]

This study presents a novel and non-destructive method for quantitatively analysing grease lubricated bearing wear by using X-ray microcomputed tomography (μCT). The efficacy of μCT to measure rolling contact wear via wear debris analysis was demonstrated, as was quantifying grease contamination and wear debris identification. Test rig experiments of grease lubricated spherical roller bearings, were performed to simulate rolling contact wear. Six grease samples were collected from two bearings at three different intervals to investigate wear progression. Results showed μCT measured wear volume increased exponentially with increasing bearing operation times. Grease cleanliness (particle counts per ml) worsened nonlinearly due to the exponential growth of wear debris over longer bearing operational times. Comparing the conventional ISO281 bearing assembly and operating condition assessment, a particle-count based method via μCT analysis provided a less subjective and dynamic assessment for quantifying grease contamination. Grease contamination was found to increase with longer operational timeframes due to the combination of wear debris growth and decreased lubrication film thickness. Finally, laminar, chunk and spherical wear particles, associated with rolling contact wear, were identified by the morphometric parameters measured by μCT. This study highlights the potential of μCT as a wear monitoring and grease quality assessment technique for railway bearing applications. • Microcomputed tomography is pioneered to measure wear in test rig bearings. • The proposed method is nondestructive and requires no sample manipulation. • The efficacy in wear measurement is proven through debris analysis in grease. • Quantitative analysis of 3D wear debris images provides wear mechanism assessment. • Grease contamination worsens with wear debris growth exponentially and lubricant film thinning. [ABSTRACT FROM AUTHOR]