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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]

In this study, finite element method (FEM) is applied to investigate the effect of material defect orientation on subsurface crack initiation in rolling bearings. First, the history of stress intensity factors (SIFs) of a subsurface cubic material defect is calculated. SIFs calculation is conducted when it is parallel to the rolling surface of a bearing ring ( φ = 0 ∘ ) under a ball rolling on the ring. Then, the effect of defect orientation, varying from φ = 0 ∘ to φ = 30 , 45 and 60 ∘ , on the history of SIFs is investigated. It is deduced that changing the defect orientation results in a threefold increase in the equivalent SIF range compared to parallel orientation. [ABSTRACT FROM AUTHOR]

Purpose: Due to high speeds, heavy loads, large slide-to-roll ratios (SRR) and other variable operating conditions, some rolling bearings that have been working in harsh conditions may experience flash temperatures in the contact area, which may result in early damage like smearing and then affect service life. This study aims to investigate the flash temperature phenomenon of rolling bearings through theoretical and experimental analysis. Design/methodology/approach: A technology for measuring temperature distribution in rolling ball on disk contact under lubrication was developed. The test-rig can simulate the ball bearing contact. The effects of working conditions such as entrainment speed, load, SRR and lubricating oil viscosity on the flash temperature were investigated. Findings: The results of the theoretical calculation and experiments indicate that the parameters promoting the reduction of film thickness in elastohydrodynamic lubrication are always related with the number of flash points, even film thickness reduced to mixed lubrication. The flash temperature is easier to happen in conditions of high SRR, heavy load, slow entrainment speed and low viscosity oil. Originality/value: This work conducts an experimental study on the flash temperature phenomenon, providing a test technology for bearing lubrication and failure investigation. Peer review: This author has opted into Transparent Peer Review available at: https://publons.com/publon/10.1108/ILT-04-2023-0104 [ABSTRACT FROM AUTHOR]

Performance of ball bearings in the motion converter subassembly of an internally driven, single-speed, torque-split, twin configuration pericyclic transmission prototype is evaluated to extend the analytical knowledge base on this innovative transmission concept. A dynamic model of the transmission is developed with high-fidelity models of the installed rolling element bearings to determine their reactions. Attention is focused on the pair of ball bearings supporting the motion converter subassembly which are subjected to a complex combination of loads, including radial and axial forces, moments, carrier motion, and possibly internal preload. Then the influence of internal axial clearance and preload on the behavior of the rolling elements is analyzed with a fully dynamic ball bearing model. Provisions to consider the carrier motion and a robust integration algorithm for component orientations are presented. Finally, a microstructure-based fatigue life simulation of the critical bearing component is performed to demonstrate the effect of clearance/preload on bearing reliability. [ABSTRACT FROM AUTHOR]

In this study, finite element method (FEM) is applied to investigate the effect of material defect orientation on subsurface crack initiation in rolling bearings. First, the history of stress intensity factors (SIFs) of a subsurface cubic material defect is calculated. SIFs calculation is conducted when it is parallel to the rolling surface of a bearing ring ( φ = 0 ∘ ) under a ball rolling on the ring. Then, the effect of defect orientation, varying from φ = 0 ∘ to φ = 30 , 45 and 60 ∘ , on the history of SIFs is investigated. It is deduced that changing the defect orientation results in a threefold increase in the equivalent SIF range compared to parallel orientation. [ABSTRACT FROM AUTHOR]

This experimental research work is conducted to determine statistical models of wear evolution and surface roughness components in a misaligned contaminated EHL rolling contact. To achieve this goal, experiments were realized on an original test rig representing the real operating conditions of gears or roller bearings. In fact, the rolling contact tests are carried out using the contact between two steel disks with the presence of misalignment defect and solid contaminants within lubricant oil. In order to investigate the influence of four operating input variables like misalignment angle (α), rotational velocity (V), load (Q), and contaminant concentration (C) on the studied responses (i.e., wear (W) and surface roughness components (Ra, Rt, and Rz)), the Box-Behnken design (BBD) was adopted. Thereafter, the results obtained were analyzed using both response surface methodology (RSM) and analysis of variance (ANOVA). It is found that the rotational velocity (V) is the most significant factor affecting the wear (W) and the surface roughness components (Ra, Rt, and Rz) of a misaligned contaminated EHL rolling contact with 75.51%, 79.2%, 89.07%, and 59.65% of contributions, respectively, whereas load (Q), misalignment angle (α), contaminant concentration (C), and two-level interaction effect (α × C and C × Q) are significant factors but have a lesser effect on the wear variability with 8.23%, 5.57%, 2.42%, 2.68%, and 2.62% contributions, respectively. It is also deduced that the misalignment angle (α) is statistically significant when studying the mean depth roughness (Rz) with 15.67% of contributions. Finally, it is revealed that the obtained higher values of determination coefficient (more than 90%) show clearly the reliable of the implemented quadratic models. [ABSTRACT FROM AUTHOR]

New demands placed on industry make it necessary to improve design, real-time monitoring and failure prediction methods for rolling bearings. This paper presents an approach for assessing how contact surface damage affects the vibration response of rolling bearings and how vibration-based monitoring shows the damage level of rolling element bearings. A new parameter named the damage factor is introduced to quantify the vibration response of rolling bearings. The analytical–numerical method for calculation of this parameter is developed based on nonlinear dynamics postulates. The developed method for damage factor calculation is tested on a particular type of radial deep groove ball bearing, and an experimental verification is performed, showing a maximum deviation of 7% in the results. The conclusions drawn from the obtained results and the potential contributions of the introduced parameters for rolling bearing design are discussed. The chosen polynomial function keeps deviations in relation to the calculated damage factor within 3% for failed areas of different sizes. [ABSTRACT FROM AUTHOR]

When the load and speed of rotating machinery change, the vibration signal of rolling bearing presents an obvious nonstationary characteristic. Stochastic resonance (SR) mainly is convenient to analyze the stationary feature of vibration signals with high signal-to-noise ratio. However, it is difficult for SR to extract the nonstationary feature of rolling bearings under strong noise background. For one thing, the frequency change of nonstationary signals makes the occurrence of SR very difficult. For another, the features of rolling bearings are large parameters and further prevent the SR method from performing well. Therefore, combined with order analysis (OA), adaptive frequency-shift SR is presented in this paper. To solve the problem of frequency change, OA is used to convert the nonstationary feature into stationary feature, which resamples the nonstationary signal in the time domain to stationary signal in the angular domain. To solve the other problem, the frequency-shift method based on Fourier transform is adopted to move the fault feature frequency to low frequency, and thus SR is more likely to occur under small parameter conditions. The simulated and experimental results indicate that not only the amplitude of fault feature but also the signal-to-noise ratio is significantly improved. These demonstrate that the fault features of rolling bearing in variable speed conditions are extracted successfully. [ABSTRACT FROM AUTHOR]

The research is aimed to understand the effect of WC/C coating on the bearing rolling elements to improve fatigue life in surface distress conditions. The 1–1.5 microns optimized coating thickness was deposited on the steel substrate using the PVD process. The coating's physical and chemical properties were analysed by X-ray diffraction, scanning electron microscope, contact profilometer, nanoindentation hardness, and micro scratch indenter. The wear properties were compared on a ball-on-disc tribometer with and without a coated specimen. The bearing tests were performed in contaminated and clean lubrication conditions to prove the coating's effect on bearing life in surface distress conditions. Results show that coated roller bearings perform at least two times that of the standard bearing. The overall benefit of less friction and wear resistance was due to the polishing action and coating transfer mechanism of multi-layer coating which increases oil film thickness between contacts and hence improve bearing life. [ABSTRACT FROM AUTHOR]

Purpose: This paper uses numerical methods to investigate the collision and skidding of rolling elements in a cageless ball bearing. This paper aims to analyse the effects of the rotational speed and number of rolling elements on the rolling element collision and skidding. Design/methodology/approach: Based on Hertzian theory and tribological theory, the collision contact model of the rolling element was established. Based on the proposed model, the differential equations of motion of the two degrees of freedom rolling element were constructed. The fourth-order Adams algorithm solved the collision contact force between the rolling elements. The sliding velocity between the rolling element and the inner and outer races was calculated. Findings: The collision frequency and slip of rolling elements can be reduced by increasing the rotational speed appropriately and reducing the number of rolling elements by one. Originality/value: The developed model can reveal the collision and slip characteristics of the rolling elements for cageless bearings. This study can provide theoretical guidance for the design and manufacture of cageless ball bearings. [ABSTRACT FROM AUTHOR]

Analysis of contact stresses in tapered roller bearings (TRBs) is an important subject in mechanical systems that involve moving and rotating parts. This is because the damage resulting from contact stresses between races and rolling elements may lead to failure and long hours of down time. To make an accurate estimation of TRB performance, it is necessary to understand the stresses experienced at the contact surfaces. In this study stresses generated by combined radial and axial loads in TRB are investigated using photoelastic experimental hybrid method. A comparison between stress behaviour of TRBs and angular contact ball bearings (ACBBs) is then made. The critical areas of stress concentrations were identified. It was found that the stresses σx and σy on races of a TRB were much lower than those on ACBB. Analysis of shear stresses showed that τxy on the TRB were more than two times those on ACBB. This difference in magnitude was explained on the basis of the orientation of rolling elements. The study also showed that under combined axial and radial loading conditions, the critical areas of stress concentrations for TRB were mainly regions where the race thickness was smallest. [ABSTRACT FROM AUTHOR]

With the rapid development of wind power industry, people pay more attention to the fatigue life prediction of wind turbine components. In this paper, the contact load and maximum contact stress of double row tapered roller bearing are calculated, and the distribution law of contact load is analyzed. The maximum contact load rolling element/raceway contact model is established by using ANSYS Workbench, and the static calculation is completed. The maximum contact stress calculated by theory is compared with the maximum contact stress obtained by simulation. The stress fatigue life was predicted by n Code. The results show that the maximum contact load on the left side is greater than that on the right side, and the maximum contact load occurs at the contact between the first roller and the outer ring with zero contact angle on the left side; the error between the theoretical calculation and simulation results of the maximum contact stress is 5.7%; the error between the theoretical calculation result and the simulation analysis result is 0.69%, which verifies the correctness and feasibility of the simulation method and model Line. The maximum contact stress and the location of fatigue failure can be observed through numerical simulation analysis, which provides reference for bearing design in practical engineering, plays a role of optimization design, and has a certain guiding significance for experiments. [ABSTRACT FROM AUTHOR]

In this paper, the dynamic behavior of rolling element bearings with localized faults on the inner and outer rings is investigated. A nonlinear mathematical model is developed with five degrees of freedom considering rotor unbalance. In this bearing model, the nonlinearity is caused by the Hertzian contact forces and the radial internal clearance. The fourth-order Runge–Kutta technique is used to solve the coupled nonlinear equations of motion numerically. Nonlinear vibration response of the rotor and bearing housing can be obtained in both time and frequency domains. An experimental verification of the numerical model is presented where experimental measurements for defective ball bearings are compared with the numerical results. Envelope spectra of the numerical results show similar behavior to that of the measured experimental signals. A parametric analysis is conducted to investigate the effect of system parameters on the nonlinear dynamic response using time waveforms, orbit plots, frequency spectra and bifurcation diagrams. The presented results demonstrate that the dynamic response shows periodic, quasi-periodic and chaotic motions because of varying rotational speeds and defect width. The proposed model contributes toward improved design and better health monitoring of bearings in practice. [ABSTRACT FROM AUTHOR]

Aiming at early detection of subsurface cracks induced by contact fatigue in rotating machinery, the knowledge-based data analysis algorithm is proposed for health condition monitoring through the analysis of acoustic emission (AE) time series. A robust fault detector is proposed, and its effectiveness was demonstrated for the long-term durability test of a roller made of case-hardened steel. The reliability of subsurface crack detection was proven using independent ultrasonic inspections carried out periodically during the test. Subsurface cracks as small as 0.5 mm were identified, and their steady growth was tracked by the proposed AE technique. Challenges and perspectives of the proposed methodology are unveiled and discussed. [ABSTRACT FROM AUTHOR]

A novel internal rotor bend actuator is presented that enables compensating strains to be applied about the rotor centre. Axial reaction tubes are used to maintain the structural stability of the bend actuator and to provide feedback on the level of actuation. The system is powered by an onboard battery and the actuation is derived from the operation of lead screw motors. The actuation is commanded wirelessly, thus providing the functionality for an autonomous rotor. The integrated rotor is demonstrated in isolation via laser tracker measurements and for the rotating prototype system. Actuated bending gave rise to radial displacements at the central point relative to shaft ends of approximately 50 µm peak-to-peak. These results validate a finite element deformation model. The rotor was levitated on active magnetic bearings, then rolling elements bearings, to demonstrate the synchronous vibration control achievable by static internal bending. The potential now exists for the commanded actuation to compensate for rotor eccentricities arising from manufacturing errors and dynamically induced unbalance for the cancellation of underlying synchronous vibration. • Novel structure bending concept. • Design of an experimental prototype. • Experimental validation of bending capabilities. • Results matching with finite element modelling. [ABSTRACT FROM AUTHOR]

While a rolling element bearing is operating, the lubricating film is desired to maintain a sufficient thickness to avoid asperity contact between surfaces. When using grease as lubricant, the film thickness undergoes evolution over time, due to the transient formation of the deposited thickener-rich layer and a bled oil film. Therefore, a model, which can address both type of film formation, is required. In this contribution, an experimentally validated numerical model is proposed by assuming the grease as a porous medium. This model can calculate the transient formation of thickener-rich layer and the oil bleeding process for grease-lubricated contacts. The predicted film thickness evolution, by superposing the thickener-rich layer and oil film, shows a reasonable agreement with the experimental result. • First transient grease film formation model based on the two-component hypothesis. • A new model for the formation of thickener-rich layer. • A new model for the grease bleeding. • Good agreement between measurements and simulations. [ABSTRACT FROM AUTHOR]

In modern frequency inverter controlled electric drive trains, parasitic electric currents can occur in rolling bearings and lead to damages of the bearing components. In the prediction of bearing currents, the bearing capacitance plays a major role. It is commonly calculated based on the Hertz ian area and the central lubrication gap height of the contact of the rolling contacts using different correction factors. In this work, a combined simulation model is presented to calculate the rolling bearing capacitance. It considers the capacitance of the rolling contact as well as the regions outside the contact domain. The model consists of an electrically extended EHL simulation of the rolling contact and a FEM simulation of the surroundings. The results of the combined simulation method show a good agreement with experimental results without the use of correction factors. • Determination of rolling contact capacitance by EHL simulation. • Cavitation and lubricant properties (density, viscosity, permittivity) considered. • Capacitance calculation of the contact surroundings by FEM simulation. • Combining capacitances of contacts and contact surroundings to bearing capacitance. • Results show good agreement with measured bearing capacitance. • Contact surroundings and varying lubricating oil level affect bearing capacitance. [ABSTRACT FROM AUTHOR]

This paper addresses the lubrication issues experienced by rolling element bearings operating under limited lubricant supply (LLS) or starvation conditions. A novel three-dimensional comb-tooth-groove (CTG) surface pattern is introduced to promote oil replenishment through unidirectional force. The transport of oil droplets on the CTG pattern is examined to evaluate this force, while groove length and depth are characterized as key factors influencing the surface force. More practically, the impact of CTG patterns on bearing lubrication under LLS conditions is assessed through experiments on bearings modified with CTG surface arrays. These modified bearings exhibit reduced torque and temperature rise, highlighting the significant advantages of CTG surfaces in enhancing bearing performance. [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]

For the case of magnetic levitation loss, the rotor of an active magnetic bearing is forced by gravity to drop onto stator laminations, and cageless touchdown bearings with high rigidity and load-bearing capacity ensure back-up support. However, the contact collision of rolling elements in a cageless bearing will lead to deterioration of bearing performance and instability of the rotor system. For this purpose, a method based on noncontact between adjacent rolling elements in cageless bearings is proposed in this paper. First, combined with space geometry, the contact process and the change in radius of rotation when a rolling element passes through a discrete groove are analysed, and a clearance between the adjacent rolling elements is generated by changing the rotation speed. Based on this, a design principle for setting a discrete groove on an outer ring raceway is proposed, and the equation for the circumferential discrete clearance for the rolling element based on bearing kinematics is given. Combined with the characteristics of discrete groove structures, a differential equation for the discrete dynamics of rolling elements with variable stiffness coefficients is proposed. We then determine the influence of the discrete groove structure on the discrete motion of the rolling element and bearing dynamic characteristics. Third, the dynamics simulation is combined with a vibration characteristics experiment and discrete motion experiment for a rolling element in a cageless bearing. Our research results show that a discrete groove design for the raceway can be used to realize stable discrete motion of the rolling element, and that such a discrete groove structure will not adversely affect the vibration characteristics of the bearing. The feasibility of the discrete design of cageless bearings with rolling element is verified, and theoretical guidance for the development and application of cageless bearings is provided. [ABSTRACT FROM AUTHOR]

The quest for high‐performance energy efficient aircraft turbine engines has led to the development of a number of high‐performance rolling element bearing materials and engine lubricants with the aim of providing superior mechanical component durability. The heat treatments/surface treatments used to achieve the desired physical and mechanical properties for these newer alloys can result in altered surface chemistry from currently used materials. Surface chemistry plays an important role during lubricant‐bearing material interactions and the formation of beneficial tribological films during component operation. The objective of this study was to analyse the tribo‐films formed on bearing surfaces and investigate the interaction of lubricant additives, specifically the phosphorus‐based anti‐wear additive tricresyl phosphate (TCP), with different bearing materials under relevant bearing operating conditions. Bearing tests were conducted on 208‐size (40 mm bore) angular contact bearings at 127°C and 154°C using gas turbine engine lubricants conforming to MIL‐PRF‐23699G at maximum Hertzian contact stresses of 3.1 GPa and 3.55 GPa. Bearing materials evaluated included AISI M50, M50NiL, nitrided M50NiL (N) and three variants of Pyrowear 675 with silicon nitride rolling elements. Tribo‐films were analysed using Energy dispersive X‐ray spectroscopy and Auger Electron spectroscopy. Results indicate that phosphorus‐rich anti‐wear tribo‐films form on all of the bearing materials studied. The applied thrust load and heat treatment had a significant effect on tribo‐film thickness. The study also suggests that current gas turbine engine lubricants formulated with TCP should form beneficial tribo‐films that enhance bearing fatigue life and performance. [ABSTRACT FROM AUTHOR]

• A universal rotor-bearing-disk system model is established. • The model considers three types of maneuvering loads. • The special vibration responses of the system under rolling, pitching and yawing maneuver loads are compared and analyzed. It is an important embodiment of fighter's comprehensive ability to have high maneuverability. Therefore, it is necessary to study the coupling dynamic behavior of rotor system in typical maneuvering flight. Based on the finite element method, a 6-node rotor-bearing-disk system model with three kinds of maneuvering loads, nonlinear contact force of rolling bearing, eccentric unbalanced force of disk and gravity field is established in this paper, and the dynamic responses of the system under rolling, pitching and yawing maneuvering is analyzed in detail. The Newmark-β method is used to solve the system model. The system responses under different rotation speeds and two given rotation speeds are mainly analyzed. The system responses under three kinds of maneuvering loads are compared and analyzed. Finally, the 7-node stepped shaft system model is used to verify the universality of the analysis results in this paper. It is found that, under the same maneuvering load value, the possibility of rub-impact and frequency division components caused by different flight modes are different. The research in this paper can provide a cognitive basis for the mechanism of system rubbing fault under different maneuvers. [ABSTRACT FROM AUTHOR]

Angular contact bearings are of primal importance in accommodating rotational mechanisms with high-speed characteristics. Their applications are centric to heavy axial and radial loads sustaining thrust loads to a single direction. In high-speed applications, factors such as centrifugal force, gyroscopic moments and relative displacements in various geometric features of the bearings are to be taken into consideration. This study focuses on establishing the contact angles, contact forces and spin speed for angular contact bearing to withstand varied rotational angular velocities. The forces experience a non-linear variation with respect to the body stiffness thus necessitating the involvement of numerical methods to converge at precise solutions through each juncture. The outer raceway of the bearing is accepted to be static with respect to the inner raceway as the input shaft for any application is predominantly affixed to the inner raceway of the angular contact bearing. Geometrical variations are determined under combined load conditions to simulate the natural working of the bearing at accelerated speeds. The analyses involve results for spatial parameters which are iteratively solved for each of the rolling elements in the bearing taken into concern. The spin speeds of the rolling elements are shown to dampen and exponentially increase with respect to their angular positions. The outputs manifested through this work can be utilized to accurately predict shift of salient design attributes of an angular contact bearings through low and high-speed applications. [ABSTRACT FROM AUTHOR]

Rolling bearings are a leading cause of equipment breakdowns in electrical machines, underscoring the significance of predictive maintenance strategies. However, the given methods require high-quality big data, which is challenging to acquire, especially for faulty cases. Simulation models offer an alternative by generating large data sets to complement experimental data. However, bearings involve complex contact-related phenomena, such as slipping and clearance. Therefore, generating realistic data comparable to the real-world necessitates accuracy. Our study presents a multibody simulation system of a motor bearing, incorporating a geometry-based polygonal contact method (PCM), which accurately captures nonlinear bearing dynamics and allows for the simulation of various contact geometries. We introduce a systematic approach to adjust the PCM contact properties for rolling bearings, referencing the well-established Hertzian theory. Both healthy and faulty bearings with a local outer ring fault were simulated. The simulated output was a relative shaft displacement, experimentally validated using a capacitive sensor. Our model successfully demonstrates the potential to employ geometry-based contacts for generating realistic data on faulty bearings with the aim of predictive maintenance. • Simulating rolling bearing dynamics using surface geometry-based polygonal contacts. • Adapting the polygonal contact method to bearings, referencing Hertzian theory. • Successfully imitating common bearing contact phenomena, such as slip and clearance. • Bearing fault analysis validation through experimental shaft displacement data. • Displacement spectrums of outer ring faults correspond to the experimental results. [ABSTRACT FROM AUTHOR]

Rolling element bearings are vital parts for rotating machinery. When a defect occurs on the surface of the bearing raceway or rolling element, giving rise to the abnormal vibration of the bearing and even the rotating machine. Thus, it is of great significance to understand the vibration characteristics of the bearing for fault diagnosis and machine condition monitoring. In recent decades, researches on defect-induced bearing vibration in machine condition monitoring have attracted increasing attention. Model-based investigation is a highly useful method for enhancing our understanding of defect-induced vibration and fault excitation mechanism of the bearing. It also serves as a basis for establishing the theory of bearing failure. With this in mind, a novel dynamic model of deep groove ball bearing (DGBB) with a localized outer race defect is proposed in this paper. In this model, the additional displacement excitation which is modelled as a piecewise function based on kinematics is considered, and the angle-based contact force is developed and modelled as a piecewise function taking into account the angular position, collision velocity, and impact force. In addition, an analytical formulation of the angle-varying effective stiffness matrix of the DGBB with a localized raceway defect of varying size is established. The proposed dynamic model is used to study the influences of different defect scenarios (i.e. angular positions and widths) on the time-varying contact stiffness, contact force, spectral characteristics, and bearing vibrations. The comparisons between the simulations and the experiments show that the proposed model is effective. • A physics and kinematics analyses based nonlinear dynamic model is proposed for defective deep groove ball bearing. • An angle-varying contact force model is deduced considering the striking force resulting from the collision of the rolling element with the trailing edge of the defect. • The time-varying additional displacement is modelled by introducing both the disconnection velocity of the rolling element from the leading edge and the angular velocity of the rolling element around the leading edge. • The contact stiffness, contact force, and contact deformation of the defective bearing are deduced and their angle-induced variations are analysed, as well as the bearing vibration behaviours. [ABSTRACT FROM AUTHOR]

Rolling element bearings are widely employed in rotating machines. The health monitoring and the residual life prediction of bearings are significant to the reliable operation of the equipment. This paper deals with the principle of a time-domain-based residual life prediction method for rolling element bearings. In particular, a quantitative evaluation of bearing degradation is performed by evaluating the sensitivity of the 13 time-domain features. Meanwhile, the optimal feature set is generated through a sensitivity evaluation analysis approach. Next, the max-min normalization and the multiple linear regression (MLR) methods are applied to construct a healthy index. Based on the healthy index, the degradation trajectory is obtained by using the locally weighted scatterplot smoothing (LOWESS) method. Two data sets generated by the outer race fault are used to verify the effectiveness of the proposed method. The experimental results show that the proposed method can realize the residual life prediction of rolling element bearings effectively. [ABSTRACT FROM AUTHOR]

Rolling element bearings (REBs) are vital parts of rotating machinery across various industries. For preventing breakdowns and damages during operation, it is crucial to establish appropriate techniques for condition monitoring and fault diagnostics of these bearings. The development of machine learning (ML) brings a new way of diagnosing the fault of rolling element bearings. In the current work, ML models, namely, Support Vector Machine (SVM) and K-Nearest Neighbor (KNN), are used to classify the faults associated with different ball bearing elements. Using open-source Case Western Reserve University (CWRU) bearing data, machine learning classifiers are trained with extracted time-domain and frequency-domain features. The results show that frequency-domain features are more convincing for the training of ML models, and the KNN classifier has a high level of accuracy compared to SVM. [ABSTRACT FROM AUTHOR]

Due to the interference of complex transmission path and noise, the weak characteristic signal of a fault in complex equipment is difficult to extract, and then it is hard to establish an index that can timely and effectively reflect the degradation state of the bearing fault. A bearing degradation state index was constructed by using moving average coarsegrained, fast iterative filtering decomposition, permutation entropy, Wasserstein distance and cumulative sum method, which realize the recognition and evaluation of bearing degradation state. On this basis, a hybrid model based on autoregressive integral moving average and nonlinear autoregressive neural network was constructed. Experimental study showed that the model could achieve accurately the residual life prediction of bearing for complex equipment. [ABSTRACT FROM AUTHOR]

To enhance the precision of rolling bearing fault diagnosis, a new rolling bearing fault diagnosis method based on improved local mean decomposition (LMD), compound multi-scale weighted permutation entropy (CMWPE), and support vector machine (SVM) is proposed. Firstly, the improved LMD algorithm is adopted to accomplish the adaptive decomposition of rolling bearing vibration signals. By computing the Pearson correlation coefficients between each component and the initial signal, the components with higher correlation are selected for signal reconstruction to accomplish the mission of noise reduction. Then, a feature extraction approach based on CMWPE is employed to extract corresponding feature parameters from the de-noised signals and construct a multi-scale nonlinear fault feature set with good stability and high recognition. Finally, the high-dimensional fault feature set is input into the SVM to achieve rolling bearing fault diagnosis. The experimental results reveal that the proposed approach can precisely distinguish various fault types of rolling bearings under the same fault degrees. For inner ring failures of different fault degrees, this method also has good identification correctness. Compared with several typical fault diagnosis approaches, the proposed method has a more trustworthy diagnosis result. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this paper is to reveal the friction and wear performance of grooves textured cylindrical roller thrust bearings with different groove dimensions under starved lubrication. Design/methodology/approach: The groove dimensions include: width of grooves (WOG, 50 µm, 100 µm and 150 µm), depth of grooves (DPOG, 7 µm, 11 µm and 15 µm) as well as groove deflection angle (GDA, 45°). A fiber laser marking system was used to prepare groove patterns on the raceways of shaft washers. The friction and wear properties of grooves textured bearings were researched through a vertical universal wear test rig using a customized roller bearing tribo-pair under starved lubrication. Static finite element analyses were conducted to reveal their surface stresses. Through the comprehensive comparison and analyses, the influence mechanism of grooves on the tribological behavior of cylindrical roller thrust bearings was proposed and discussed. Findings: When grooves textured bearings run under starved lubrication, their average coefficients of friction (COFs) and wear losses are all significantly reduced and much lower than those of smooth group. The influence of DPOG on the COF curves is significant, while the influence of WOG on the COF curves is a little weak. The influence of groove dimensions on the surface stresses of grooves textured bearings is weak, whether the WOG or DPOG. In this work, when the WOG is 100 µm and the DPOG is 15 µm, its average COF and wear loss are both the lowest, 0.0066 and 0.61 mg, respectively. Compared with the data of smooth group, its friction coefficient is reduced by 75.3% and its mass loss is reduced by 95.8%, showing a significant improvement in this condition. Originality/value: This work can provide a valuable reference for the raceway design and reliability optimization of rolling element bearings. [ABSTRACT FROM AUTHOR]

Purpose: Rolling bearing operation under mixed and boundary lubrication conditions may lead to heavy adhesive or abrasive wear, which may lead to wear-induced rolling bearing failure. The purpose of this paper is to investigate the wear protection capabilities of different grease compositions at varying temperatures. It is considered that the temperature influences the lubrication conditions, the behaviour of grease components, namely, bleed oil and thickener, as well as the tribofilm formation due to tribo-chemical interactions between additives and surfaces. Design/methodology/approach: In this study, four different greases were produced on the basis of a mineral base oil by varying the thickener and the addition of ZDDP. Various grease-lubricated rolling bearing experiments were conducted in a wide temperature range from 0°C to 120°C. Subsequently, the wear pattern, tribofilm formation and grease structures were analysed. Thereby, the influence of the different grease thickeners and the performance of ZDDP as a common antiwear and extreme pressure additive was evaluated. Findings: The results show a strong temperature-dependency and allow a classification of temperature ranges concerning wear protection. At low temperatures, all greases provide a very good wear protection without the evidence of additive-based tribofilm formation. In the experiments at elevated temperatures, ZDDP tribofilms were formed. The formation depends on the thickener type: in comparison to lithium thickener, polyurea thickener favours more protective tribofilms at the same temperature. The experimental results show that medium temperatures in the range of 40°C–60°C are critical concerning wear due to the insufficient tribolayer formation and limited load carrying capacity of the grease. Originality/value: Temperature is a key operating parameter for grease lubrication in roller bearings. The experimental work enables consideration of different impact pathways of temperature by combining roller bearing tests and microanalysis. [ABSTRACT FROM AUTHOR]

Considering the difficulty in the diagnosis of compound faults in rolling bearings, the paper combines Intrinsic Time-scale Decomposition (ITD) and Singular Value Decomposition (SVD) for extracting the characteristics of compound faults from rolling bearings. Rotational components obtained from ITD decomposition are denoised according to Singular Value Decomposition algorithm; signal is reconstructed by denoised rotational components; at last, characteristics of compound faults of rolling bearings are extracted by Hilbert spectrum envelope of reconstructed signal. In validation, the paper has made a comparative study on the proposed ITD-SVD method and conventional one based on ITD algorithm and PCA method, and the result shows that ITD-SVD method works better on noise control and thereby provides more precise extraction of characteristic frequency of compound faults from rolling bearings of aero-engine. [ABSTRACT FROM AUTHOR]

It is challenging to extract weak impulse features from vibration signals corrupted by strong noise in mechanical fault diagnosis. Due to its simple calculation, fast convergence and easy implementation, K-singular value decomposition (K-SVD) has been widely used in rolling bearing fault diagnosis. However, it fails to consider the influence of noise and harmonics on atoms learning from impulse characteristics, which results in many irrelevant atoms, and then increases the difficulty of extracting the impulse features in bearing fault signals. Therefore, a clustering K-SVD-based sparse representation method is proposed in this paper and it is combined with the particle swarm optimisation (PSO)-based time-varying filter empirical mode decomposition (TVF-EMD) for rolling bearing fault diagnosis. The PSO-based TVF-EMD is developed to automatically decompose the original signal to eliminate the impact of noise and harmonics on the impulses in the signal. Then, the clustering K-SVD method is applied to perform dictionary learning on the sensitive component containing impulses to obtain a redundant dictionary of atoms with obvious impulse patterns. Finally, the orthogonal matching pursuit (OMP) algorithm is introduced to extract the fault features from rolling bearing vibration signals. The experimental results show that the proposed method can improve the robustness of the dictionary atoms to noise and achieve the extraction of rolling bearing fault features. [ABSTRACT FROM AUTHOR]

Electrical capacitance method has been applied in measuring the elasto-hydrodynamic lubrication film thickness in rolling element bearings since 1970s, due to its feasibility of measuring film thickness directly in metallic components and its simple theory. In the current article, a summary on the evolution of the method and the corresponding issues relating to the film thickness measurements is given. The evolution of electrical capacitance method and other developed electrical capacitance methods in measuring the film thickness are discussed. Especially, the two existing methods of converting measured capacitance into film thickness are highlighted. One is to calculate the capacitance in the Hertzian contact area and the dielectric constant of the lubricant. The other is to apply calibration tests which are then used to transfer the measured capacitances into film thicknesses. The strengths and weaknesses of the two methods are also explored and discussed based on published researches. [ABSTRACT FROM AUTHOR]

A method of combining autocorrelation function with cyclostationary theory and Hilbert envelope analysis is proposed and applied to extract characteristic frequency of rolling bearing. Meanwhile, mean power ratio is calculated and used to identify the fault types of aero-engine rolling bearing based on single-channel casing vibration signal. To verify the effectiveness of proposed method, a comparing analysis is carried out between traditional studies and proposed new method. Furthermore, the influences on the extraction of characteristics and calculation of mean power ratio are taken into account, including the ones of sensor installation position, fault types, type of experiment rigs, failure mode and rotational speed of rolling bearing. The result shows that the proposed method can diagnose running conditions and identify fault types of rolling bearing accurately and effectively just by single-channel casing vibration signal. [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]

This investigation entails analysis of 520 butterfly formations (BFs) and non-metallic inclusions without BFs in two RCF-tested roller bearings to elucidate the influence of inclusion characteristics and stress level they are subject to, on the initiation and growth of BFs. The results show duplex inclusions, though least frequent in the bearing steels, exhibit the highest butterfly formation rate comparing with pure sulphide/oxide inclusions. It is also found that larger inclusions and those with smaller aspect ratios are more prone to butterfly formation; BF wing length decreases with the increase of inclusion aspect ratio; BF orientation is significantly influenced by inclusion size and stress level; stress magnitude appears to either impede or facilitate BF wing growth depending on BF orientation. [ABSTRACT FROM AUTHOR]

In this paper, we present a Boundary Element methodology to numerically investigate the operation of a viscoelastic rolling element bearing in steady-state conditions. The methodology is fully general, able to deal with any real linear viscoelastic material, and relies on the ad hoc definition of steady-state viscoelastic Green's functions that intrinsically take into account the circular geometry of the domain. From an applicative point of view, the assessment of this contact problem is crucial: we show that the distribution of the load among the rollers is really different from what is predicted in purely elastic conditions, with some rollers eventually losing the contact with the raceways for some speed values. This has dramatic consequences not only on the rolling element bearing durability but may impact the rotor dynamics of the system supported by the bearing. Furthermore, our analysis assesses the viscoelastic torque pointing out the sources of hysteretic dissipation. Finally, to corroborate our model, numerical predictions for a rolling element bearing with the outer ring made of Polytetrafluoroethylene (PTFE) are compared, with good agreement, to experimental outcomes. • A novel Boundary Element formulation assesses polymer rolling bearings mechanics. • Analysis of the load distribution among the rollers as a function of the speed. • Assessment of the hysteretic dissipation as a function of the load and the speed. • Experimental corroboration for a Polytetrafluoroethylene (PTFE) rolling bearing. [ABSTRACT FROM AUTHOR]

The bearing race conformity is a design parameter that determines the degree of contact between rollers and races. This paper investigates the effect of race conformity on wear distribution in a railway spherical roller bearing under boundary lubricated condition in which contact behaves like a dry contact. The results showed that the traction/micro-slip distributions were substantially dependent on the level of conformity. The wear is found to be highly sensitive to the race conformity, with lower conformity resulting in lower wear. For example, 5.2% increase of conformity factor, a parameter that represents race conformity mathematically, reduces worn area by 52% in inner contact that is 60% in outer contact where conformity factor increase is 5.8%. This is mainly due to high value micro-slip being truncated at the edges as the traction distribution is compressed into the smaller contact patch. The bearings with ceramic rolling elements show lower wear than for steel rolling elements due to lower wear coefficient. The higher elastic modulus of ceramic causes the traction magnitude to be higher in the ceramic-steel case over the steel-steel case. Therefore, race conformity can be taken into consideration to optimize roller bearing wear life. • The influence of race conformity on the contact and wear characteristics are approached analytically. • The traction/micro-slip is analysed at different position of the loaded zone of a roller's revolution around the races. • An increase of race conformity by 5.2% increases wear area by 52%. • Wear distribution and traction/micro-slip are investigated for different material combinations. • Different material combinations show different level of wear and mainly due to friction/wear coefficients and elastic properties. Wear level changes with the material combination due to friction/wear coefficients. [ABSTRACT FROM AUTHOR]

• An impact force function with time-varying characteristics is proposed. • A dynamic model considering time-varying excitation named TIEM is proposed. • TIEM has typical time domain characteristics and frequency domain characteristics. • TIEM has a better generalization capability than conventional models. • TIEM has a significant improvement on the fault frequency components. • TIEM's vibration is positively correlated with rotational speeds and defect sizes. Accurately establishing a dynamic model of rolling bearings is significant for understanding the fault mechanism and analyzing the motion characteristics under different performance states. Since the contact process of rolling element defect is more complicated than that of race defect, the research on its characteristics is usually simplified to a certain extent. However, the excitation of the rolling element defect area is closely related to the rotational speed and the size of the defect, the commonly used displacement form of fault excitation can hardly reflect the mechanical characteristics of the actual rolling element fault. A time-varying displacement excitation function of the rolling elements is used to characterize the change of the contact gap between the rolling elements and the inner and outer races. According to the time-varying displacement excitation function, a time-varying impact force excitation function of the defective rolling element is proposed which comprehensively considers defect sizes and the rotational speeds. A four-degree-of-freedom bearing dynamics model based on Hertz basis theory is correlated with time-varying excitation, and the accuracy of the model is confirmed by comparison with the processed experimental signal. Based on the mechanical model and experimental data, the influence of the rotational speeds and defect sizes on the vibration characteristics of the bearing rolling element fault is analyzed and summarized, which provides theoretical support for investigating the mechanism of the bearing rolling element fault. [ABSTRACT FROM AUTHOR]

This paper proposes a method for detecting insufficient lubrication in rolling bearings, by utilising a low cost MEMS ultrasonic microphone. We run a set of grease lubricated bearings under load, alternating between good and insufficient lubrication conditions by adjusting speed and temperature, over an 18 day experiment, followed by a short validation experiment on a different set of bearings on a secondary test rig. Vibration signals are recorded from an ultrasonic microphone, using a purpose built prototype sensor, then band-pass and high-pass filtered and subsequently analysed using statistical time-domain features. The viscosity ratio Kappa of the lubricant is used as a metric for quality of oil-film formation, and is calculated throughout the experiment from rotating speed and temperature. The results are compared with the predictions from a linear regression model and a simple Neural Network trained on ensembles of three and ten selected features. The three Hjorth's Parameters activity , mobility and complexity calculated on high-pass filtered microphone signals from the experiments show a good correlation with the viscosity ratio Kappa. When combining these, using a Linear Regression model or a simple two layer Neural Network model, we are able to predict the viscosity ratio with good precision. The proposed method may be used to assess the quality of oil film formation in bearings during operation under varying speed and temperature conditions. [ABSTRACT FROM AUTHOR]

The acquisition of complex fluxes inside a Tapered Roller Bearing (TRB) via Particle Image Velocimetry (PIV) is an experimental challenge. This can be successfully performed by exploiting a special test rig having the outer ring manufactured with sapphire. In the present paper, the velocity field in the region between cage, rollers and outer race have been captured via PIV in a fully flooded lubricated TRB. The experimental conditions have been reproduced numerically via Computational Fluid Dynamics (CFD). The comparison of PIV results with CFD ones showed excellent consistency. It has been observed that, in the target domain, the tangential velocity of the lubricant is greater than those of the cage. In addition, in the proximity of the edges of the rollers, squeezing effects due to high gradients of pressure have been recorded. The distribution of flow rates due to the pumping effect in different regions of the TRB have been estimated. • Lubricant fluxes in a tapered bearing were studied experimentally and numerically. • Rotational speeds up to 2500 min-1 in fully flooded lubrication were tested via PIV. • Velocity fields obtained via PIV and CFD showed excellent consistency. • Squeezing and edge effects were obtained by means of CFD and observed through PIV. • The total flow rate in fully flooded lubrication conditions was estimated via CFD. [ABSTRACT FROM AUTHOR]

Traction in lubricated rolling and sliding contacts plays an important role in the performance of several machine elements. Many of such elements are subject to spin motion, which can affect their performance. Recent studies have also highlighted the effects of the contact scale on the traction behaviour. Nevertheless, their combined effect was not investigated to date. The present study, therefore, analyses the effect of both on the traction in heavily-loaded lubricated contacts. To this end, a novel semi-analytical traction prediction model was developed considering spin motion. The results show that increasing the contact size and/or spinning speed leads to a reduction in traction coefficient and contact efficiency due to thermal effects. These conclusions have important practical applications designing machine elements. [ABSTRACT FROM AUTHOR]

Rolling element bearings, when subjected to small oscillating movements or vibrations, run the risk of being damaged by mechanisms such as Standstill Marks and False Brinelling. Damages resulting from these phenomena can decrease bearing fatigue life and increase wear-induced friction torque. These failures do not correlate well with standard life estimation approaches. Experimental studies play a crucial role in gaining knowledge in this area. The review integrates knowledge from experiments ranging from single contacts to laboratory and full-scale bearings in wind power and aerospace applications. The generalization is achieved using a non-dimensional amplitude parameter that relates rolling element travel during an oscillation to the Hertzian contact size. The review encompasses testing methods, procedures, reporting practices, result scaling, and application-specific considerations. [ABSTRACT FROM AUTHOR]

In this paper the lubrication mechanism of lithium grease lubricated ball bearings in the bleed phase is described. Oxidation plays an important role and therefore grease life "in air" and grease life "in nitrogen" is studied in real bearings. It is shown that grease life is strongly dominated by oxidation but that this is by far not deterministic. Oxidation starts up at a certain time, the induction time, which is the point at which the anti-oxidants have been consumed. This induction time is a function of the bearing operational conditions and the oxygen concentration. Oxidation leads to loss of base oil and loss of lubricity, partly repaired by replenishment and oil release from the grease reservoirs (bleed). [ABSTRACT FROM AUTHOR]

Rolling bearings are machine elements found in a wide field of applications. They are reliable even under the toughest conditions. When bearings fail to meet their expected life, the consequences are increased down time, loss of revenue and missed delivery. Hence, it is important to know the bearing theoretical fatigue life. However, unfortunately, it sometimes happens that a bearing does not attain its calculated rating life. There may be many reasons for this—heavier loading than has been anticipated, inadequate or unsuitable lubrication, careless handling, ineffective sealing, improper mounting and improper clearance. This article describes the failure of a conveyor bearing in rolling contact fatigue. The investigation consists of visual observation, chemical analysis, characterization of microstructures using optical microscopes and hardness test. The study also calculates the bearing fatigue life (L10) under these operating conditions. Surface-initiated rolling contact fatigue, leading to spalling, is a life-limiting failure mode in bearings. Ferrography test, discussed in this paper, indicates fatigue spalling. Analysis suggested that the conveyor bearing failed near its calculated fatigue life and the failure occurred in rolling contact fatigue. Periodic schedule, after calculating L10 life, for changing the bearing and scheduled ferrography checks can eliminate this type of unplanned breakdown. [ABSTRACT FROM AUTHOR]