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This paper presents a rolling contact fatigue life prediction model for bearing steel. In the initial stage of rolling contact, the gradient structure appears in the subsurface region of bearing steel and the hardness shows a gradient distribution along the contact depth direction due to the roller compaction effect. This indicates that the fatigue resistance of bearing steel varies in the subsurface region. Besides, each subsurface material volume element is subject to different stress cycles. Based on Weibull theory, the survival possibility of subsurface volume elements is formulated. Then the rolling contact fatigue life is evaluated considering the stress state and anti-fatigue performance of each elementary volume of the subsurface material. According to the phenomenon and assumption, the model proposed for gradient material was applied in the rolling contact fatigue life prediction of the bearing steel GCr15 and validated with the fatigue experiment data in the open literature. Furthermore, the accuracy of the proposed model results was compared with the traditional empirical rolling contact fatigue life prediction models. [ABSTRACT FROM AUTHOR]

This study presents the results of modelling the rolling contact of the elastic sphere and the elastic half-space in the presence of a thin intermediate viscoelastic layer which properties are described by an elastic nonlinear Winkler body in the normal direction and a viscoelastic Maxwell body in the tangential direction. The analytical–numerical approach for the estimation of contact fatigue damage, accumulated in the elastic half-space under rolling friction conditions, is developed. The proposed model can be used, in particular, to study the effect of mechanical properties of the friction modifiers (elastic moduli and relaxation times) and its thickness as well as the relative slippage on the formation of the surface and under surface contact fatigue cracks in rails. The results of the analysis can also be applied for the estimation of efficiency of solid lubricants in rolling contacts under given operating conditions. [ABSTRACT FROM AUTHOR]

Bearing is the most vulnerable key part in rotating machine and bears important influence on the safety of equipment. Weakness and complexity are the two features of fault characteristic information carried by signals in the early stage of fault. For that, a fault is difficult to be recognized correctly. To identify a compound failure of bearing, the paper has brought forward a new self-adaptive option method for component signals that are sensitive to failure feature information of bearing. The sensitivity of kurtosis to bearing failure is exploited and the influence of signal complexity on the extraction of failure feature information is taken seriously, the paper has proposed the self-adaptive option method for component signals that are sensitive to failure feature by combined kurtosis with Complexity parameter included in Hjorth parameters. Furthermore, as the mid-value represents the general level of signal and is not affected by larger or smaller data, with the mid-values of kurtosis and Complexity parameter as the boundary, the paper has chosen the component signals which can more comprehensively show the failure features of bearing. Additionally, by principal component analysis (PCA), component signals selected are blended and reconstructed. Finally, by the Hilbert envelope spectrum of signals reconstructed, failure types of bearing are identified. To verify the effectiveness of presented method, the presented method is compared with conventional method on the basis of the exactly consistent data. The result indicates that the proposed method is superior to the traditional one in extracting fault information and identifying the multiple failure types of bearing. [ABSTRACT FROM AUTHOR]

Wheel-rail impact, which arises from structural discontinuities and short-wave defects, becomes more serious with higher train speeds and larger axle loads. The large impact load can accelerate the deterioration of vehicle-track components and induce a high level of impact noise. This paper aims to better understand the characteristics of wheel-rail impact and redevelop corresponding mitigation measures. First, a well-validated vehicle-track vertical interaction model with a singular rail defect is built up considering nonlinear Hertz contact. Then, the simulated wheel-rail impact force is characterized in both the time and frequency domains with different running speeds and defect geometries employing continuous wavelet transform. The identified characteristic frequencies are correlated to the track resonance modes. Afterward, a parameter sensitivity analysis of railpads, ballast, roadbed, and suspensions is performed to obtain the mitigation measures of wheel-rail impact. The results show that the wheel-rail impact force can be characterized by four stages in the time domain, the quasi-static stage before the impact, the forced vibration, the free vibration, and the quasi-static stage after the impact, respectively. Four characteristic frequencies are identified in the wheel-rail impact response: f 1 at 45 Hz, f 2 at 100 Hz, f 3 at 260 Hz, and f 4 at 810 Hz. Among them, f 4 has the dominant vibration energy and is determined together by the pinned-pinned resonance mode and the defect excitation frequency. Characteristic frequencies f 1, f 2, and f 3 correspond to the ballast, sleeper, and rail resonance modes, respectively, which are independent of the defect geometry. The increase of railpad stiffness can effectively reduce the maximum wheel-rail impact force and thus the impact factor. Larger railpad stiffness and damping can significantly reduce the dominant vibration energy at about 810 Hz of f 4. This work can contribute to the optimization of vehicle-track parameters for a new design of more impact-resistant railways. [ABSTRACT FROM AUTHOR]

Rail corrugation is very serious in Cologne egg fastener track; effective control measures are still lacking. The cause of the corrugation wear on a curved metro track is analyzed based on the friction-induced vibration theory. A finite element model is established to study the frequency domain and time domain features of the friction-induced oscillation of this system. The influences of the fastener spacing and the fastener support length on the corrugation wear are investigated to develop countermeasures. The simulation results show that the friction-induced vibration of the wheel-track system is the wavelength-fixed mechanism of the corrugation wear of rail of the curved Cologne egg fastener track. There are two reasons why the low rail corrugation wear is more serious. The contact resultant force between the low rail and the wheel is obviously bigger than that between the wheel and the high rail, resulting in a higher wear rate of the low rail. The contact force fluctuation of the low rail caused by the friction-induced vibration is more severe, resulting in a higher corrugation wear evolution speed on the low rail. The friction-induced oscillation cannot be eliminated only by adjusting the fastener support length and spacing. However, the long-wavelength corrugation wear instead of the more harmful short-wavelength corrugation wear can be produced by adjusting the fastener support length and the fastener spacing to alleviate the influence of corrugation wear on the vehicle-track system. [ABSTRACT FROM AUTHOR]

Based on the measured spectra of rail roughness and track structures longitudinal roughness, the rail grinding limit is studied with the help of an established coupled dynamic metro vehicle–track model and a rolling contact fatigue model. The results indicate that metro rail grinding control should be regulated according to corrugation wavelength range and operating speed. Based on the rolling contact fatigue model, longer wavelength of rail corrugation has less influence on the wheel rolling contact fatigue. For the metro lines with a maximum operating speed of 80 km/h, the average levels of rail corrugation in the wavelength ranges of 30–65 mm, 65–125 mm, and 125–250 mm should be less than 5.4, 24.8, and 33.8 dB re 1 μm, respectively; for the ones with the operating speed of 80–120 km/h, the corresponding average corrugation levels in the three wavelength ranges should be less than 4.4, 9.8, and 29.8 dB re 1 μm, respectively. [ABSTRACT FROM AUTHOR]

A method based on minimum entropy deconvolution with convolution adjustment and zero frequency filter is presented for the identification of weak faults in rolling element bearings. Localized fault present in rolling element bearings causes periodic impulses in the bearing vibration signal. The zero frequency filtering of the bearing vibration signal keeps only the localized disturbances at the impulse locations while attenuating the non-impulsive components of the signal. The effectiveness of zero frequency filtering depends on the strength of impulses present in the measured faulty bearing signal in time domain. In the present work, Minimum entropy deconvolution adjusted is used as a preprocessor to improve the strength of impulses in the measured time-domain bearing signal. The effectiveness of the proposed algorithm is tested with simulated signals for the faulty bearing vibration at different levels of added Gaussian noise. The algorithm is also validated using experimental bearing vibration dataset. Results from the proposed algorithm are compared with the results of the zero frequency filter and local mean subtraction-based technique for rolling element bearings' fault identification. The proposed algorithm performs better detection in case of a weak fault signal. [ABSTRACT FROM AUTHOR]

When a wheel rolls over a railway rail, it 'sees' a varying stiffness downwards because the rail is periodically supported by sleepers, leading to parametric excitation of the rail/wheel system. This study investigates the importance of parametric excitation on railway noise generation. Because the problem is non-stationary, it is modelled in the time domain. Rail and wheel impulse response functions, together with an iteration scheme to match boundary conditions in the rail/wheel contact patch, yield rail and wheel response plus contact force at each wheel position on the rail. Forward velocity and rotation of the elastic wheel are accounted for. Feedback coupling between response and force takes part in the excitation. Numerical simulations show that, for a rail on stiff pads, parametric excitation is a major excitation mechanism, above all leading to increased excitation and noise levels in a broad frequency region around the pinned–pinned frequency. [ABSTRACT FROM AUTHOR]

Applying a bearing preload of machine tool spindle produces positive effects, including increased stiffness, rotation noise reduction, increase in shaft precision, position adjustment during operation, and prevention of rolling element resonance and rotating slip, along with a significant extension of the bearing lifespan. A variable preload technique is a method that improves the bearing performance by appropriately varying the preload applied to the bearing according to the spindle rotation speed and machining condition. In this study, a novel variable preload method utilizing a Terfenol-D actuator has greater power and more displacement and force than those of other transducer materials such as piezo elements or nickel alloys. Terfenol-D has greater power and more displacement and more force. A prototype of a spindle for the variable preload system using Terfenol-D was fabricated, and the axial force and displacement of the bearing were measured during a running experiment. In order to assess whether the proposed variable preload device can effectively apply preloading to the bearing, a comparative analysis was conducted between the theoretical and empirically obtained values of the bearing axial direction displacement. Through the comparative analysis, the real applicability of the proposed structure was confirmed. [ABSTRACT FROM AUTHOR]

This paper presents a complete model to estimate the effects of wheel wear on the dynamic behavior and ride comfort of a railway vehicle. A co-simulation of the vehicle dynamics modeled in ADAMS VI-Rail and wear evolution modeled in MATLAB is performed in a loop. The outputs from the vehicle dynamics simulation are used to compute the wear evolution, which in turn affects the vehicle dynamics. The local contact parameters, such as normal contact force, tangential stresses and slip, etc., and wear distribution for each cell of the contact surface are estimated with the help of Kalker's simplified theory of rolling contact and Archard's wear model, respectively. The wear distribution and smoothening of the wheel profile are obtained for a short travel distance and are then scaled up for larger travel distance. The worn wheel profile is updated in the vehicle dynamics model after every 10,000 km of travel for further dynamic analysis and this process is repeated until either the critical dynamic performance or wheel wear limits are reached. Several new results emerge by considering both acceleration and braking on a tangent track with sinusoidal irregularities. Critical speed appears to increase initially and then decrease quickly, whereas worn wheels give better ride comfort in both lateral and vertical directions as compared to new wheels. According to the results in this work, wheels may be recommended for re-profiling or replacement much before the critical wear depth recommended in maintenance guidelines is reached. [ABSTRACT FROM AUTHOR]

A load-sharing-based mixed lubrication model, applicable to cam–roller contacts, is developed. Roller slippage is taken into account by means of a roller friction model. Roughness effects in the dry asperity contact component of the mixed lubrication model are taken into account by measuring the real surface topography. The proportion of normal and tangential load due to asperity interaction is obtained from a dry contact stick–slip solver. Lubrication conditions in a cam–roller follower unit, as part of the fuel injection equipment in a heavy-duty diesel engine, are analyzed. Main findings are that stick–slip transitions (or variable asperity contact friction coefficient) are of crucial importance in regions of the cam where the acting contact forces are very high. The contact forces are directly related to the sliding velocity/roller slippage at the cam–roller contact and thus also to the static friction mechanism of asperity interactions. Assuming a constant asperity contact friction coefficient (or assuming that gross sliding has already occurred) in highly loaded regions may lead to large overestimation in the minimal required cam–roller contact friction coefficient in order to keep the roller rolling. The importance of including stick–slip transitions into the mixed lubrication model for the cam–roller contact is amplified with decreasing cam rotational velocity. [ABSTRACT FROM AUTHOR]

A finite element-based simulation was carried out to investigate the effects of friction-induced thermal load on rail under varied wheel slip conditions. The surface temperature rise from six different percentage slips (1%, 1.5%, 2%, 5%, 8.5%, and 10%) at the contact interface was examined for eight-wheel pass. The residual stresses and accumulated plastic strains evolved by the effect of localized temperature rise are estimated. Analytical formulation for conduction mode of heat transfer at the contact patch is used to estimate the temperature distribution. The interaction of thermal-elastic-plastic field conditions is obtained by a proposed simulation model. This is implemented in commercial finite element software ANSYS 14.0. In order to capture the steep thermal gradient beneath the contact surface, refined mesh is used in the upper layers up to a depth of 2 mm of the simulation domain. For better manifestation of thermally affected material layers, a temperature dependent bilinear-kinematic hardening material condition is applied. Results indicate the maximum temperature rise at about 0.6a from the trailing end in the contact ellipse of semi-major axis a. At higher slippage conditions the initial pearlitic rail steel gets converted to martensite which is often observed on rail surface as white etching layer known to be associated with rolling contact fatigue. The study reveals the mechanisms of thermally induced defects observable on rail surface. The outcomes, in addition, can provide useful information for the development of thermo-mechanically superior rail steels. [ABSTRACT FROM AUTHOR]

The bispectrum of rolling element bearing compound faults contains abundant fault characteristic information, and how to extract the fault feature effectively is a key problem. The fault diagnosis method of rolling element bearing compound faults based on Sparse No-Negative Matrix Factorization (SNMF)-Support Vector Data Description (SVDD) is proposed in the paper. The figure handling method SNMF is used firstly in fault feature extraction of the bispectrums of rolling element bearing different kinds of compound faults and the sparse coefficient matrices of the bispectrums are obtained. The sparse coefficient matrices are used as training and test input vectors of SVDD. At last, the three kinds of rolling element bearing compound faults (inner race outer race compound faults, outer race rolling element compound faults and inner race outer race rolling element compound faults) are classified correctly. In order to verify the advantages of the proposed method, the diagnosis results of the same three kinds of rolling element bearing compound faults based on No-Negative Matrix Factorization (NMF)-SVDD is used as comparison. The proposed method provides a new idea for fault diagnosis of rolling element bearing compound faults. [ABSTRACT FROM AUTHOR]

In 2008, the Journal of Mechanical Engineering Science was approaching its 50th anniversary and the editorial board arranged some personal contributions from those who had been material in the journal’s success. In response to this initiative, the authors spoke informally to Ken Johnson about his life and work. However, typically modest in his approach, Ken was reluctant to see the article published during his lifetime, and so it has remained in the ‘bottom drawer of the desk’ ever since. But now, following Prof. Johnson’s passing in September 2015 we thought it appropriate to publish our brief article with minor modifications, and hope that it will serve as a memorial to the enormous contribution he made to his chosen field of study. [ABSTRACT FROM AUTHOR]

Bearings are an essential component in all types of rotary equipment. Erosion in the bearing is unavoidable due to radial and axial forces permanently acting on the bearing during the course of rotation. In order to avoid catastrophic breakdown of the equipment, it is a fundamental requirement to monitor the bearings. The scope of the existing bearing fault diagnosis techniques in the literature is limited to only pre-known bearing and machinery. On the contrary, this research develops a generalized protocol for detecting ‘inner’ and ‘outer’ race bearing faults for any unknown rolling element bearing. This automated bearing failure detection model tunes itself adaptively to any type of rotary equipment and the bearing. Automated bearing failure detection is based upon using wavelet transform to scan the spectral contents and applies envelop detection. The raised asynchronous energy in the envelop spectrum is a potential indication for the bearing faults. [ABSTRACT FROM AUTHOR]

Inner wall profile of the cylinder in a rotary vane compressor (RVC), which influences the motion characteristics of vanes, suction volume, friction characteristic, etc., plays an important role in the performance of the compressor. This work mainly aims at the profile design of a new cylinder for a double-acting RVC with harmonic profile cylinder on the basis of not changing integrate size. According to the relation between cylinder profile and vane motion characteristics, a method for the cylinder profile design is proposed in this paper. With an assumed vane motion, equations of the cylinder profile, cell volume of the compressor as well as pressure angles between vanes and cylinder inner wall are constructed preliminarily. And then through adjusting parameters and optimization with an independently developed procedure, a new cylinder with the so-called combined profile is obtained. Theoretical analysis of the cell volume variations and the pressure angles between vanes and cylinder are conducted. The results show that there is neither rigid impulse nor soft impulse between vanes and cylinder due to the vane continuous motion including displacement, velocity and acceleration. And the pressure angles between vane and cylinder and working volume of the compressor with the new profile cylinder are superior to harmonic profile cylinder, which is useful for the reduction of friction power in the operation of compressor. Experiments show that the cooling capacity and COP of the test refrigeration cycle with the proposed combined profile cylinder is higher than the compressor with harmonic profile cylinder. And the volumetric efficiency and isentropic efficiency of the compressor with combined profile cylinder have better performance. This method can be applied to the design of the cylinder for multiple-acting rotary vane compressors, rotary vane expanders and vane pumps. [ABSTRACT FROM AUTHOR]

Rolling element bearings are vital components in most rotating machines. Bearings often operate in harsh environments where manufacturing imperfections, misalignments, and fatigue can result in reduced component lifespan. These failures are often preceded by changes in the normal vibration of the system. Modeling and detecting these vibrational anomalies is common practice in predicting machine failure. This paper develops and implements a novel approach to detecting bearing vibration anomalies in the time–frequency domain. The performance of the new approach is quantified using both simulated and experimental bearing vibration data. In these ground-truth experiments, the proposed time–frequency method successfully detects anomalies (>98% true positive) using short time spans (<0.1 s) with low false alarm rates (<1% false positive). Using experimental data, this time–frequency approach is shown to outperform one-dimensional time series analysis techniques. [ABSTRACT FROM AUTHOR]

This paper deals with the failure of an elastohydrodynamic lubrication rolling contact, operating in highly contaminated media. To achieve this goal, an original experimental device was built and then successfully used to investigate the effects of three operating parameters, called contaminant concentration (C), rotational speed (V), and load (Q) on the evolution of wear, W, and arithmetic mean surface roughness, Ra. The influence of the above mentioned parameters is statistically explored using the analysis of variance (ANOVA). Mathematical models for wear and surface roughness were also established using the response surface methodology by employing multiple regression method. From this experimental research, it is clearly shown that the contaminant concentration is the major factor leading to the fast failure of machine elements. Finally, the obtained results justify and confirm the lifetime reduction of mechanisms in highly contaminated media. [ABSTRACT FROM AUTHOR]

Rolling element bearings are critical mechanical components in rotating machinery and fault detection in the early stages of damage is important to prevent their malfunctioning and failure. Vibration monitoring is the most widely used and cost-effective monitoring technique to detect, locate and distinguish faults in rolling element bearings. This paper purposes single hidden layer architecture for fault diagnosis of rolling element bearings. The particular of this proposed architecture is its ability to generalize for solving both basic classification and fault identification. The network uses the features of time-domain vibration signals with normal and defective bearings. The Multi Layer Perceptron (MLP) was trained and tested with a set of experimental data obtained from previous experiments developed by FEG, CWRU and RANDALL laboratories. The results show the effectiveness of the MLP to diagnose the machine condition for the various data used. [ABSTRACT FROM AUTHOR]

Sliding contact has negative influence for the performance of gears in most situations, such as frictional loss, pitting, micro-pitting, etc. To avoid sliding contact, this paper discusses the fundamental geometrical characteristics of spiral bevel gears of continuous pure-rolling contact. Differential geometry, gearing kinematics, and conjugate curve meshing method are used to derive the general mathematical model of spiral bevel gears of continuous pure-rolling contact. Simplified equations that continuous pure-rolling contact bevel gears must satisfy are derived. An example is represented to explain and verify this model. The theoretical results benefit further studies on design and manufacturing of spiral bevel gears of heavy loads and high efficiency. [ABSTRACT FROM AUTHOR]

A theoretical and computational framework for the analysis of thermomechanically coupled, frictional, stationary (steady-state) rolling contact based on an Arbitrary Lagrangian–Eulerian (ALE) kinematical description is presented. The finite element method is employed in a numerical implementation featuring two-dimensional cylinder–plate rolling contact, with a contact formulation incorporating mechanical and thermal frictional interaction. The ALE formulation is noted to allow for linearization of the governing equations, localized mesh refinement, a time-independent description of stationary dynamics, velocity-independent contact interface modelling and so on. Numerical simulations show the model to be able to capture, for example, stick/slip behaviour and a range of thermal phenomena, including the effect of convective cooling of the cylinder due to the contact with the plate. [ABSTRACT FROM PUBLISHER]

Wear, rolling contact fatigue, and plastic deformation are the major failure modes of railway wheels and rails. Proper analyses of the failure mechanisms as well as improvement in design and maintenance require an accurate evaluation of the stress and strain states. Solution of frictional rolling contact between wheel and rail in elasto-plasticity seems, however, still to lack in the literature. This paper presents a model for such a solution. A 3D finite element model is built up to simulate the rolling contact. The focus is on the tangential problem, namely the distributions of surface shear stress and micro-slip as well as the distinction of areas of adhesion and slip in the contact patch. With the presented model the assumptions of half space, linear elasticity and quasi-static or steady state, which are often employed in existing solution of rolling contact, are dropped. A bilinear elasto-plastic material with isotropic hardening is employed to examine the effects of plasticity on frictional rolling. It is found that when plastic flow occurs, the contact patch in the rail top changes from an ellipse into an egg shape; the cross influence between the normal and tangential contact problems become stronger: the normal solution is not independent of the tangential solution any more, and the tangential solution is greatly affected by the normal solution. The model can be applied to investigation of the relationships between material properties, plastic deformation, frictional work, wear, and crack initiation. Such relationships may help in better understanding the occurrence of corrugation, head checks, and squats, and may further be used for design of fatigue resistant materials and profiles of wheel and rail. [ABSTRACT FROM PUBLISHER]

In this work, a thermomechanically coupled rolling problem with nonlocal contact, Coulomb’s friction and heat exchange boundary conditions, for incompressible rigid-plastic, temperature-, equivalent strain- and strain-rate-dependent materials, is considered. A coupled variational formulation, consisting of a nonlinear variational inequality for the velocity, a nonlinear variational equation for the temperature and an evolution equation for the equivalent strain, is derived. A variable stiffness parameters method is proposed, its convergence is proved and existence and uniqueness results are obtained. [ABSTRACT FROM AUTHOR]

Feature extraction plays an important role in fault diagnosis. It is critical to extract the representative features for improving the classification performance. An intelligent fault diagnosis method based on Marginal Fisher analysis (MFA) is put forward and applied to rolling bearings. The high-dimensional features in time-domain, frequency-domain and wavelet-domain are extracted from the raw vibration signals to obtain rich faulty information. Subsequently, MFA excavates the underlying low-dimensional fault characteristics embedded in the high-dimensional feature space by preserving local manifold structure. Thus, the optimal low-dimensional features are obtained to characterize the various fault conditions of rolling bearings and finally fed into the simplest k-nearest neighbor classifier to recognize different fault categories. The diagnosis results validate the feasibility and effectiveness of the proposed fault diagnosis method, compared with the other three similar approaches. [ABSTRACT FROM AUTHOR]

To simulate the contact and separation of wheels and rails accurately, the stiffness between them should be correct. This paper developed a nonlinear moving wheel element based on a simple point contact scheme to simulate moving train problems, where the element stiffness is set to a power function directly fitted from the finite-element result of the wheel and rail contact analysis. The finite-element result of the wheel/rail contact analysis indicates that the changes in vertical stiffness with changing contact forces can be accurately fitted by using the proposed power function, and the horizontal stiffness can be simply regressed using a constant. The validated example in this paper shows that the nonlinear moving wheel element can simulate the complicated contact and separation problem correctly, both in the displacement and contact force fields, and the major advantage is that a fine mesh is not necessary in the moving train contact analysis. [ABSTRACT FROM AUTHOR]

The objective of this study is to investigate the adhesion characteristics of wheel/rail under oil contamination with consideration of surface roughness using a three-dimensional model of wheel/rail in rolling contact. A partial elastohydrodynamic lubrication theory is employed in the model. An under-relaxation revision on the film thickness is used to keep the simulation procedure stable. The dependence of the wheel/rail adhesion coefficient on train speed, surface roughness amplitude, parameter of roughness orientation and axle load is studied under oil contamination. Moreover, the numerical solutions of a two-dimensional model are compared with those of the three-dimensional model. In addition, a good agreement has been found between the numerical results and the experimental results obtained by a JD-1 wheel/rail simulation facility, which consists of a small wheel roller serving as locomotive or rolling stock wheel and a large wheel roller serving as rail. [ABSTRACT FROM PUBLISHER]

In this study, experimental tests to assess rolling contact fatigue in uncoated and coated steel substrates with TiN and CrN coatings are presented. A thrust bearing tester was used. The tests were carried out in lubricated conditions at 1560 r/min, using a contact pressure of 2.09 GPa. The surface damage was analyzed by optical microscopy, scanning electron microscopy, and energy dispersive spectroscopy. The substrates coated with CrN showed a fatigue life above 100 million cycles. On the other hand, with TiN, the time for crack nucleation was much shorter, approximately 60 × 104 cycles. [ABSTRACT FROM AUTHOR]

Polymer nanocomposite has received great research interest in design of engineering components owing to its remarkable improvement in tribological characteristics. Rolling contact fatigue is a predominant failure mode of the many functional components like gears, bearings, cams, ball screw rods and rail wheels. Nanosize clay fillers were dispersed into the polymer using melt intercalation method to produce polymer nanocomposite material. Injection-molded disc-type specimens were made to run against each other on twin-disc test rig designed in-house. To understand the behaviour of the materials, rolling contact fatigue behaviour against different contact loads under constant speed were studied. Rolling contact fatigue testing of polymer nanocomposite has revealed significant difference from the pristine PA6 behaviour in failure modality and temperature rise. Addition of nanoclay to polymer although improved the modulus and strength of the nanocomposite, deteriorated the rolling contact behaviour. Rolling contact fatigue performance of PA6 was better than that of the clay-reinforced polymer nanocomposite under all tested conditions. Polymer nanocomposite materials have shown poor wear resistance as the specific wear rate was calculated to be higher for PNC materials under rolling contact fatigue conditions. Difference in surface temperature rise in PA6 and polymer nanocomposite has led to the different failure mechanism and reduction in rolling contact fatigue life of polymer nanocomposite materials. [ABSTRACT FROM AUTHOR]

In vibration analysis, fault feature extraction from strong background noises is of great importance. Frequency band entropy based on short-time Fourier transform illustrates the complexity of every frequency component in the frequency domain, and it can be used to detect the periodical components hidden in the signal. This article shows how the frequency band entropy offers a robust way in detecting faults even when the signal is under strong masking noises. Furthermore, frequency band entropy provides a way of blindly designing optimal band-pass filters. The filtering signal combined with envelope analysis is helpful in fault diagnosis. The effectiveness of the proposed method is demonstrated on both simulated and actual data from rolling bearings. [ABSTRACT FROM AUTHOR]

Optimisation of railway track maintenance requires knowledge of how a deteriorated track geometry will affect subsequent loading and damage of the track. This is the scope of the current study where, in particular, the influence on track shift forces and rolling contact fatigue is investigated through numerical simulations. To this end, track geometries are obtained from field measurements. Lateral irregularities are extracted and scaled to represent different levels of geometry deterioration. Multibody simulations of dynamic train–track interaction featuring two freight wagon types are performed under different operational conditions. Track shift forces and rolling contact fatigue damage are further evaluated from simulation results. It is found that track shift forces tend to follow a normal distribution for moderate levels of lateral track geometry irregularities, and that an approximate linear relationship between standard deviations of lateral irregularities and track shift forces can be established. The relation between lateral track irregularity magnitude and rolling contact fatigue is more complex. Increasing levels of lateral irregularities will decrease the fraction of curve length affected by rolling contact fatigue for sharp curves, whereas for shallow curves it increases. As detailed in the article, this is caused by the lateral movement of the contact point as imposed by the track irregularities. Furthermore, the influence of wheel/rail friction and wear is investigated. [ABSTRACT FROM AUTHOR]

There are always some differences in the diameters of the rolling elements that are less than manufacturing tolerance, which are known as off-sized defects. These diameter differences of the rolling elements assumed to be with identical size in the traditional bearing analysis affect the load performance of the bearing greatly and make the evaluation of the load distribution in the bearing difficult. In this study, a static model was developed to investigate the effects of diameter differences among cylindrical rollers on the load performance in a bearing. In the model, the diameter and order of each roller were defined arbitrarily. Contact judgments between all the rollers and the raceways were done constantly in the solution process, so that compatibility of deformation of the rollers and raceways need not be considered, which was different from other traditional methods. The effects of roller off size and its arrayed order in the bearing on the load distribution were analyzed. It was found that the effect of one off-sized roller on the load distribution was serious. Also, equal space or ordinal array of the multiple or full off-sized rollers was much better than random array. Furthermore, the relative diameter of the rollers determined the load distribution in the bearing. This article can help to further study the dynamic performance of the bearing with the off-sized cylindrical roller in the future. [ABSTRACT FROM PUBLISHER]

The correct prediction of shear stresses in lubricants applied to concentrated rolling/sliding contacts has been an issue of intense debate for many years. Traction testers of various kinds such as two-disc roller rigs or ball on disc apparatus have been extensively used in order to obtain experimental data, as well as, more recently, molecular dynamics simulations. Several, partly competing, phenomenological models have been developed to describe the dependence of shear stresses on various parameters. Evidently, the importance lies in the need to predict and reduce friction, or, more accurately, resistance to motion of rolling element bearings in order to increase efficiency of machines and vehicles. Also, it plays a crucial role in design and performance of traction drives. As a prerequisite, experimental data for a wide variety of fluids were obtained from two-disc roller tests with a wide variation of contact pressures, rolling speeds and slide-to-roll ratios. Following earlier investigations, the amount of slip created by the elastic deformation of the discs was separated from the contribution of the fluids and their rheological properties. In accordance with experiments of Jacobson a threshold pressure in the fluid was identified which marks the onset of a nearly linear relationship between a limiting shear stress and pressure. However, this threshold does not appear to be constant but rather declining with decreasing hydrodynamic film thickness respective of rolling speed, while the slope changes to a lesser extent. When measurements were extended far into the mixed lubrication regime close to the limiting case of boundary lubrication, the shear stress/pressure relationship became quasi-Coulomb with a virtually zero threshold pressure. These results have successfully been used to predict the friction torque of angular contact ball bearings and the traction characteristics in toroidal drives. [ABSTRACT FROM AUTHOR]

This article describes the influence of rheological properties on the bearing torque characteristics of the lithium soap greases with five types of base oils. The greases used had different yield stress depending on the base oils even with the same thickener concentration. Measurement of bearing torque was conducted for a deep-groove radial ball bearing by using a bearing test apparatus. The bearings filled with greases initially exhibited high torque but showed gradual decrease in the torque with prolonged rotation, where the greases with higher yield stress showed larger normalized torque decrease. Observation of bearing after the rotation revealed a tendency that the greases with larger normalized torque decrease had been pushed aside in the raceway by channeling. This implied that the greases with higher yield stress tended to show channeling. On the other hand, the greases with lower yield stress circulated within the bearing by churning and showed smaller normalized torque decrease. These behaviors were explained in terms of the yield stress of the greases and the shear stress to entrain the greases into the contacts. Observation of grease structure was made with atomic force microscopy showed that the greases whose thickener network structure was distributed more densely had higher yield stress. [ABSTRACT FROM AUTHOR]

Highly localized stresses generated at the gauge corner of the outer rail cause fatigue cracking. The longitudinal bending stresses in the rail underhead radius position are of special interest, as tension spikes have been identified at this location during in-track measurements under high axle load conditions. The tension spike is a result of vertical and lateral head bending on the web. This effect is highly localized and is additional to the stresses generated due to vertical and lateral bending of the whole rail profile (the so-called global bending). This study examined contact and bending stresses by modelling the rail on a discrete foundation using finite elements and by considering the loading to be a fully slipping elliptical Hertzian contact patch. The analysis revealed that the tensile longitudinal stress was highly dependent on several service conditions: the contact patch offset from the rail centreline, the ratio of lateral (L) to vertical (V) loads, the direction of lateral traction, foundation stiffness and seasonal temperature variations. The tension spike increases, and the depth below the contact surface at which the stresses become tensile reduces, as the contact patch offset and/or the L/V ratio increases. Both these enhance the tendency for rolling contact fatigue cracks to turn downwards and become transverse defects. This is because an increase in tensile bending stresses together with both residual and thermally induced stresses can facilitate cracks to turn perpendicular to the tensile stresses once they reach a critical length. Shear traction towards the gauge corner was found to be the most damaging phenomenon. [ABSTRACT FROM AUTHOR]

High-speed vehicles are exposed to crosswinds that can result in the overturning of the vehicle. As part of the vehicle homologation process, the characteristic wind curve (CWC) must be calculated to determine the maximum vehicle velocity under different wind conditions. European Standard EN 14067-6 presents different approaches for studying this matter, from a two-dimensional (2D) model to a full multi-body model. The key to the problem rests in the uncertainties inherent in a multi-body model: characterizing its suspension elements and obtaining its aerodynamic coefficients. This paper compares a 2D model with a multi-body model of the same vehicle, and presents the advantages and disadvantages of each one. Results show that a 2D model is valid for graphing the CWC and sufficient for studying the basics of the overturning process. Furthermore, a wheel unloading time signal is also studied. It is concluded that the simplification process can modify the transitory response but that the maximum wheel unloading remains constant. Finally, a study of the wheel/rail contact is performed to check if the contact model has an influence on the calculation of the CWCs. [ABSTRACT FROM AUTHOR]

In the 1970s, a rolling contact fatigue defect that was christened a squat was identified on the British railway network, primarily at first on the West Coast Main Line. Two productive decades of international research on squats followed, which later contributed to a rapid understanding of gauge corner cracking, which differs in detail but is similar in many important respects to a classic squat. In the last 10–15 years, a rail defect that is superficially similar to the classic squat has appeared on several railways. This has been investigated in some detail, initially in Australia and more recently also in Europe as part of the Innotrack project. These investigations have both assumed that the investigated defect is a classic squat. This paper reviews research on the squat and on its younger cousin. It forms the basis for a companion paper that presents original observations from track and detailed metallurgical examinations of specimens of the more recent squat-type defect. The review in this paper is used in the companion paper to identify features of the two types of defects that are similar and those that are significantly different. [ABSTRACT FROM AUTHOR]

A theoretical and numerical framework to evaluate rolling contact using an arbitrary Lagrangian–Eulerian (ALE) formulation is established. A finite element formulation is implemented featuring cylinder–plate contact, automated mesh refinement, non-reflecting boundary conditions, and the ability to incorporate surface roughness through user-defined gap functions. Presented examples include rolling contact on a corrugated surface and negotiation of a surface discontinuity. Sensitivity and validation analyses are presented and show the model to be robust and the trends in parametric responses to be reasonable as compared to results in literature. Owing to the ALE formulation, the model can be kept very compact and the computational demands very modest. [ABSTRACT FROM AUTHOR]

In practice, the tilting roller occurs widely in rolling bearings. In order to investigate the lubricating mechanism of tilting rollers in rolling bearings, a contact between a tilting cylindrical roller and an infinite plane is assumed in the present paper. Using the multi-grid method, a numerical solution has been obtained for the isothermal elastohydrodynamic lubrication of the contact. The film thickness and pressure with different tilt angles have been given. Results show that the property of the tilting roller’s lubrication is different from that of the parallel roller contact investigated in the past, and asymmetry is common both for the film thickness and the oil pressure under tilting conditions. Moreover, the larger the tilt angle, the smaller the minimum film thickness, and the more easily the local wear occurs in bearings. The effects of the maximum Hertzian pressure, velocity parameter, and length and end profile radius of the roller on the lubricating performance of the contact have been discussed. The conclusion can be made that better lubrication of tilting roller contact needs light load, high velocity parameter, short length, and larger end profile radius of the roller. Comparisons between the starved and fully flooded lubrication in the tilting roller contact have been given, and it has been found that starvation status can worsen the lubrication and reduce the life of roller bearings. [ABSTRACT FROM PUBLISHER]

The deformation and stress state due to overrolling near the rough surface of a rail is studied. Then a criterion for the inclination of a shear localization zone (SLZ) is introduced. Furthermore, the recent finding that the crack tip driving forces becomes infinite for a crack embedded in a SLZ is recalled. Experimental observation shows also that the fracture toughness in the SLZ is significantly reduced. All these facts point to the development of a crack, the so-called head check if it arises in a regular pattern, in the SLZ, whose predicted direction agrees well with observations. [ABSTRACT FROM AUTHOR]

Exploring an effective assessment index is significant for performance degradation assessment, which has been proposed to realize equipments’ near-zero downtime and maximum productivity. In this paper, the Kolmogorov-Smirnov test based on an autoregressive model is proposed to assess the performance degradation of rolling bearings. Accelerated life test (in Hangzhou Bearing Test and Research Center) of rolling bearings was performed to collect vibration data over a whole lifetime (normal-fault-failure). The result shows that the Kolmogorov-Smirnov test method can obviously detect incipient weak defects and can reflect performance degradation process well. In particular, it can detect abnormal stages earlier before the bearing steps into failure, which is significant in condition maintenance and prognosis. [ABSTRACT FROM PUBLISHER]

The pressure–viscosity coefficient of a traction fluid is determined by fitting calculation results on accurate film thickness measurements, obtained at different speeds, loads, and temperatures. Through experiments, covering a range of 5.6 < M < 12 000, 2.1 < L < 17.5, film thickness values are calculated using a numerical method and approximation formulas from 12 models. It is concluded that, to assess the pressure–viscosity coefficient of the fluid, the Chittenden et al. approximation formula applied to circular contacts is the best choice, having an inaccuracy in between (−15%, +11%). This expression has been used far outside the regime of the numerical data where it was based upon. [ABSTRACT FROM AUTHOR]

The article presents an extensive survey of experimental data on rolling contact fatigue (RCF) crack shape and propagation characteristics in rails removed from service, where such cracks are angled to the rail axis. The data include re-analysis of previously published experimental data to extract crack shape information and new experimental work on crack shapes at different stages in the early RCF life. Periods from initiation (ratcheted ‘flake cracks’) have been considered through very early growth to the limit of one prior austenite (PA) grain and on to rail-head visual cracks. Techniques included multi-sectioning through single cracks and crack zones, on used rail and test discs, to build up real three-dimensional (3D) data on crack shapes and propagation characteristics. This data have been compared with the UK rail system guidance charts relating to visual crack length and respective vertical depth; all data fell within the indicated guidance zones. The configuration of such angled cracks, typically found in curves, so aligned due to the vector of both lateral and longitudinal traction, rather than just axially, was identified as an important case for modelling. A fracture mechanics-based model has been developed to predict modes I and II stress intensity factors for such cracks covering multiple PA grains. An important geometry effect is revealed by which a contact approaching a crack angled to the rail axis is effectively ‘offset’ from the approach direction considered in 2D models, thereby resulting in lower predicted peak stress intensity factor values, compared with 2D, for the prediction of crack growth rates. [ABSTRACT FROM AUTHOR]

Head checking (HC) as a surface-initiated rolling contact fatigue damage in rails has been a problem for many railways. Countermeasures such as optimal design of wheel and rail profiles, optimal design of the vehicle-track interaction system, HC-resistant rail materials, etc. are being developed. Such development requires a better understanding of the relationship between the operational loading conditions of the rails and the initiation of HC. This article presents an effective non-Hertzian method for evaluating the stress state on the rail and wheel surfaces under operational conditions, so that HC initiation location and orientation can be directly related to the stress. It is shown that the HC initiation location and orientation derived from the computed stress state are in agreement with those observed in the field. [ABSTRACT FROM AUTHOR]

The wheel-rail rolling contact finite-element model based on arbitrary Lagrangian-Eulerian finite-element method (FEM) is developed and applied to the wheel-rail steady-state rolling contact analysis. Based on the wheel-rail steady-state rolling contact analysis, the wheel profile wear prediction methodology is developed and applied to wear of the wheel flange and rail gauge corner when the heavy-haul train passes on sharp curve track. The vehicle dynamic model is built in the ADAMS software, and the forces of the axle boxes acquired from the vehicle system dynamic model are loaded on the model of three-dimensional non-linear finite-element steady-state analysis for wheelset rolling contact process. Steady-state rolling contact analysis based on three-dimensional non-linear finite element is solved by the ABAQUS software. In the FEM simulation, a material model with bilinear kinematic hardening property is used. The wear modelling is based on the Archard's wear model. Laplacian smoothing with area weights is used to smooth the meshes of wheel and rail. Finally, the simulation results of a heavy-haul train wheel are analysed. [ABSTRACT FROM AUTHOR]

This study investigates the influence of a machining-induced white layer on the performance of hard machined surfaces in rolling contact. Based on the residual stress and microhardness distribution of a specimen without a white layer and one with a white layer, fatigue parameters are computed to investigate its effect on the fatigue performance. Fatigue tests are then performed to substantiate the computations. It is noted that the white layer moves the crack initiation depth to a deeper location at low maximum Hertzian stresses, whereas it moves the crack initiation depth to a shallower location at the highest maximum Hertzian stress. The white layer can increase the maximum shear stress at crack initiation depth by 54 per cent. The white layer can reduce the crack initiation life by 75 per cent, while reducing the crack propagation life by 89 per cent. Accordingly, it can reduce the fatigue life by 85 per cent. The effect of the white layer on crack initiation life, crack propagation life, and fatigue life decreases significantly as the loading increases. The presented results demonstrate that the white layer induces a highly variable change in fatigue parameters, and its effect on fatigue performance can be significantly lessened if the loading is increased. [ABSTRACT FROM AUTHOR]

Tests in a full-scale roller rig, a full-scale linear test rig, and a twin-disc machine are numerically evaluated and compared in terms of rolling contact fatigue loading. From previously evaluated contact patch sizes, a Wöhler curve relationship is established and matched towards experimentally established fatigue lives. In addition, non-linear finite-element simulations are carried out. Key data needed for the numerical evaluations, as well as difficulties in translating experimental data to numerical models are highlighted. A key parameter here is the interfacial wheel—rail friction. Additional simulations were carried out to establish the latter. However, the conformal contact in the linear test rig makes such simulations very uncertain. [ABSTRACT FROM AUTHOR]

A methodology for simulating wear, rolling contact fatigue, and plastic deformation for a mixed traffic situation in switches and crossings (S&C) has been developed. The methodology includes simulation of dynamic vehicle—track interaction considering stochastic variations in input data, simulation of wheel—rail contacts accounting for non-linear material properties and plasticity, and simulation of wear and plastic deformation in the rail during the life of the S&C component. To find means of improving the switch panel design, the geometry of a designed track gauge variation in the switch panel has been represented in a parametric way. For traffic in the facing and trailing moves of the through route, an optimum solution was identified and then validated by evaluating a wide set of simulation cases (using different wheel profiles). The optimum design includes a 12 mm maximum gauge widening. Several crossing geometries were investigated to find an optimal geometric design for the crossing nose and wing rails. The MaKüDe design showed the best performance for moderately worn wheel profiles in both running directions (facing and trailing moves). In connection with reduced support stiffness (e.g. elastic rail pads), this crossing design is predicted to lead to a significant reduction of impact loads and consequently provide a high potential of life-cycle cost reduction. [ABSTRACT FROM AUTHOR]

Based upon Hilbert envelope spectrum and support vector machine (SVM), a method for the fault diagnosis of rolling bearing is proposed in this paper. Targeting the modulation characteristics of rolling bearing fault vibration signals, the Hilbert transform based envelope spectrum analysis is used to extract fault bearing features. In the envelope spectrum, character frequencies are quite clear and can be used as a reliable source of information for bearing diagnosis. Basic SVM is originally designed for two-class classification problem, while bearing fault diagnosis is multi-class case. A new bearing fault diagnosis system based on "one to others" SVM algorithm is presented to solve the multi-class recognition problems. Practical vibration signals measured from rolling bearings with ball fault, inner race fault and outer race fault are analyzed by the proposed method. The results show that the proposed method provides accurate diagnosis and good diagnostic resolution. [ABSTRACT FROM AUTHOR]

The objective of this paper is to investigate geometric and material parameters that affect the interaction of multiple pre-existing (initiated) cracks due to rolling contact fatigue (RCF) loading conditions. In particular, the behaviour of short cracks (head checks) in railway rail is studied. Parameters of interest are initial crack angle and spacing, distribution of initial crack lengths, width of the load/contact zone, and the material properties (in particular, the friction coefficient). Furthermore, the sensitivity of the finite element (FE)-mesh density is investigated. An open question of particular interest is the effect of crack interaction, e.g. shielding, on the prevailing crack spacing. In view of all uncertainties of the material model as well as the three-dimensional geometric complexity of the RCF problem, it is important to obtain a good understanding of the sensitivity of parameter changes. This is achieved in the presented investigation, although it is carried out using simplifying assumptions such as plane strain, linear elasticity, and Hertzian pressure distribution. [ABSTRACT FROM AUTHOR]

The performance of grooved air bearings in micro systems is analysed and discussed. The modified molecular gas lubrication (MMGL) equation is utilized as the governing equation for the gas film to include the effect of gas rarefaction. The gas rarefaction is significantly affected by two important parameters (Knudsen numbers (Kn) and accommodation coefficients (ACs)). The Poiseuille and Couette flowrate correctors (QP and QC) are introduced in the MMGL equation to extend the lubrication theory (compressible Reynolds equation) for arbitrary Kn and tangential momentum accommodation coefficients or ACs. At a specific operating condition, the transient MMGL equation is linearized by small variations in film thickness and pressure. The linearized MMGL equation is then solved by finite-element method to obtain the dynamic pressure distributions. Therefore, the dynamic coefficients (stiffness and damping coefficients) are obtained by integrating the dynamic pressure over the bearing surfaces. [ABSTRACT FROM AUTHOR]