Search

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]

This work characterises wear debris/particles generated naturally in grease-lubricated spherical roller bearings (SRBs) used in urban rolling stock. Morphological examination revealed the most active wear in grease lubricated SRBs is predominantly associated with the rolling/sliding contact and adhesive mechanisms, resulting in chunk, laminar and spherical wear debris found most frequently. Morphological transitions in spherical and chunky wear debris associated with bearings' service life was seen for the first time in railway SRBs. Interestingly, the formation of chunky wear debris was not necessarily governed by rolling contact fatigue and crack propagation mechanisms seen in oil lubricated systems, but rather associated with the collapse of larger spherical wear debris. Additionally, the surface complexity observed on individual debris, associated with rolling-sliding wear is also discussed. The findings add to the sparse knowledge of wear debris formation and their contribution to grease degradation, particularly for railway SRBs. Furthermore, an estimate of the contamination level of the SRBs was obtained by carefully adapting the fluid lubricant standards. The combination of these results will allow for improved wear prediction and the optimisation of bearing maintenance practices. • Seven types of wear debris naturally generated in grease lubricated rolling stock SRBs was identified and studied. • Formation of wear debris in the railway SRBs is mostly associated with rolling/sliding contact mechanism. • Morphological evolution of spherical debris linked with service life was seen for the first time in grease lubricated SRBs. • Chunk wear debris found in grease lubricated SRBs were governed by collapse and/or fracture of large spherical wear debris. [ABSTRACT FROM AUTHOR]

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]

Experiments are conducted for investigating the effect of normal pressure, sliding amplitude and oscillating sliding frequency on friction, wear coefficient and threshold energy for wear activation of 52100 high carbon bearing quality steel (ASTM A295) during a false brinelling test. The cylinder-on-cylinder set-up is used. The investigation showed that the friction coefficient decreases with increasing normal pressure and increases with increasing sliding amplitude; however, there is no influence of an increase in oscillating sliding frequency. Similarly, the wear coefficient decreases with increasing normal pressure and increases with increasing sliding amplitude; however, unlike the friction coefficient, it increases with an increase in oscillating sliding frequency. Different conditions do not have a significant influence on the threshold energy for wear activation. By incorporating a varying friction and wear coefficient with changing sliding parameters, the analytical prediction for false brinelling are improved by 10–50% over the constant parameter model. • The effect of varying conditions on friction, wear coefficient was investigated. • The effect of different parameters on threshold energy for wear activation was investigated. • The results were then used to improve and validate the false brinelling models developed previously. [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]

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]

Wheel squeal noise is a common problem that occurs in railway systems especially on curved tracks. These tonal noises are usually found at high frequency, typically over 1 kHz. The cause of the squeal noise remains unclear and could be different under varied conditions. Several mechanisms that could cause wheel squeal, including falling friction and mode coupling, have been proposed in literature. Most existing lab experimental investigations were focused on the squeal noise caused by falling friction with vertical contacts. As a result, the squeal noise generated by mode coupling could be missed due to the absence of a non-vertical contact angle. In this work, a two-wheel test rig has been designed with curved wheel profiles to achieve adjustable contact angles with lateral components. Experimental and numerical modal analysis of the two-disk system was conducted to determine the dynamic characteristics for exploration of mode coupling effects. Using a set of benchmark parameters predicted to be the cause of significant mode-coupled instability, squeal noise was found at frequencies higher than the existing falling friction experimental tests as reported in the literature. The frequency and amplitude measured in the experiments agreed with the predictions of the analytical mode coupling model. Further experiments varying control parameters, contact angle, angle of attack and direction of rotation were performed, confirming that the new squeal noise was caused by mode coupling. • The first experimental verification of mode coupling wheel squeal mechanism using two-disk testrig. • Experimental generated squeal noise level and frequency agreed well with the analytical model prediction. • Additional experiment with reversed rotation confirmed the identified squeal noise was caused by mode coupling. • Further parametric experiments varying contact angle and angle of attack were conducted, and the results were compared with the analytical model prediction and literature. [ABSTRACT FROM AUTHOR]

Abstract An adaptive finite element model was developed to predict false brinelling in a cylindrical bearing, during the transportation of new trains and then compared with experimental measurements. The model was developed, based on the Archard wear equation, using ABAQUS and developing an ABAQUS UMESHMOTION code. A false brinelling monitoring system was designed and installed to record the vibration and rotational motion of the bearing, during the train's road and sea transportations and were used as inputs for the FE model. A set of laboratory experiments were conducted to determine wear and friction coefficients and the threshold energy for the bearing that were used in the simulation process. To compare the FE results with a real case, a profilometry measurement of false brinelling marks in a damaged bearing was performed. According to the FE wear profile results, rotational displacement of the bearing is the most likely cause for false brinelling during transportation. Due to the wear energy being below the threshold, it was predicted that no false brinelling occurred due to lateral and axial vibrations at the roller. The existence of the partial slip area, in the contact, causes the development of W shape wear marks that was seen in the profilometry measurement of the damaged sample. Highlights • An adaptive finite element model was developed to predict false brinelling in a bearing. • A monitoring system was designed to record the vibration during the train's transportations. • Laboratory experiments were conducted to determine bearing material coefficients. • Profilometry measurement of false brinelling marks in a damaged bearing was performed. • Rotational displacement was the most likely cause for false brinelling. [ABSTRACT FROM AUTHOR]

The locomotive traction motor electric dynamics and its impact on the rail and vehicle have not been investigated deeply in transient wheel–rail contact conditions. Such transient traction behaviour could be more significant to dynamic traction performance and track degradation (i.e. corrugation formation, fatigue, wear, etc.) than steady state behaviour. In order to study this, detailed numerical simulations are performed to investigate the locomotive multi-body dynamic response to a change in contact conditions with an AC and DC electrical traction motor respectively. In particular, creep response, locomotive vibration, and dynamic normal and tractional forces are determined using a developed full scale locomotive dynamics model. The model includes the detailed AC and DC motor dynamics. Further investigation has been undertaken to understand the wear caused during and after the change of friction conditions from dry to wet and wet to dry. The result shows the GT46Ace locomotive AC drive can achieve higher traction efficiency compared to the equivalent DC drive running under notch 8, especially in the wet condition. It is also demonstrated that the AC drive produces slightly lower wear on average than the DC drive after the transient. However, the transient dynamic oscillation of wear caused by the AC drive is significantly higher than the DC drive. [ABSTRACT FROM AUTHOR]

Abstract: Tool wear manifests in change of roughness of roll surfaces and governs the surface quality of both coated and uncoated products. Decrease of friction and wear in the roll–strip interface will stabilize the performance of the cold roll forming (CRF) mill and ensure uniform process output. The scope of this paper includes an experimental study of adhesive wear of hardened tool steel blocks sliding against a mild steel wheel and field observation of tool wear in the CRF of zinc coated mild steel. Wear mechanisms are identified for the materials interacting during the CRF process. The results include an empirical value of tool wear coefficient for D2 steel sliding against unlubricated uncoated hot rolled AISI C1020 mild steel. [Copyright &y& Elsevier]

An experimental and numerical study was developed to investigate the influence of radial load and the amplitude of rotational and lateral vibrations on false brinelling damage in railway cylindrical roller bearings. For this objective, a novel false brinelling test-rig was designed and fabricated to conduct both linear vibration and rotational displacement tests. A reciprocating pin-on-cylinder wear test was also conducted to determine the friction and wear coefficients of the bearing, under different frequencies. These experimental results where then used to verify a developed finite element model for false brinelling of an individual roller. The reciprocating wear test results show that the friction coefficient is almost constant and does not significantly, change, by changing the frequency. The wear coefficient, however, can be estimated by an exponential function of the frequency. The experimental and numerical results showed that reducing the bearing static radial load and increasing the amplitude of linear and rotational vibration, intensifies the false brinelling damage. It was also shown that by increasing the bearing radial load, the false brinelling wear profile changes from a U-shape to W-shape. • The influence of radial load and vibrations on the false brinelling damage of bearings was investigated. • A novel false brinelling test-rig was designed to recreate false brinelling. • A 3D FE model was developed and verified with the experimental results. • A set of wear tests was developed to determine the wear parameters at different frequencies. [ABSTRACT FROM AUTHOR]