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Bearings with partial function grooves as cageless bearings related to magnetic floating bearing protection have characteristics, such as fast offsetting of the impact force caused by rotor fall, and they gradually become important parts of ultra clean and cryogenic transportation systems. However, the functional failure mechanism of the bearing, which is caused by functional groove wear, is not clear. Therefore, this paper establishes a force–motion intrinsic model of particles inside the functional groove, which is based on the discrete element method, which it itself combined with the functional groove damage evolution trend analysis. Then, a hyper-quadratic surface model of inter-particle contact is established to simulate the time-varying friction coefficient of the functional groove by combining particles of different sizes to form particle clusters. Additionally, as the boundary condition, EDEM is used to solve the contact motion state of rolling element rolling through the functional groove for one week to obtain the overlap between particles and contact force change law. The results show that the wide side of the functional groove wears more seriously than the narrow side, and the rolling element leaves the functional groove with more impact than when it enters the functional groove, and the functional groove wears more seriously. In this paper, through the study of local functional groove wear of cageless ball bearing, we propose to characterize the damage extension of functional groove by using the number of particle fracture and motion trend in discrete element method, and this study provides theoretical guidance for the design of cageless bearings. [ABSTRACT FROM AUTHOR]

This article presents a performance investigation of a fault detection approach for bearings using different chaotic features with fractional order, where the five different chaotic features and three combinations are clearly described, and the detection achievement is organized. In the architecture of the method, a fractional order chaotic system is first applied to produce a chaotic map of the original vibration signal in the chaotic domain, where small changes in the signal with different bearing statuses might be present; then, a 3D feature map can be obtained. Second, five different features, combination methods, and corresponding extraction functions are introduced. In the third action, the correlation functions of extension theory used to construct the classical domain and joint fields are applied to further define the ranges belonging to different bearing statuses. Finally, testing data are fed into the detection system to verify the performance. The experimental results show that the proposed different chaotic features perform well in the detection of bearings with 7 and 21 mil diameters, and an average accuracy rate of 94.4% was achieved in all cases. [ABSTRACT FROM AUTHOR]

Copyright of China Mechanical Engineering is the property of Editorial Board of China Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of China Mechanical Engineering is the property of Editorial Board of China Mechanical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Bearings are one of the pivotal parts of rotating machines. The health of a bearing is responsible for the hassle-free operation of a machine. As vibration signatures give intimations of machine failure at an earlier stage, mostly vibration-based condition monitoring is used to monitor bearing's health for avoiding the risk of failure. In this work, a simulation-based approach is adopted to identify surface defects at ball bearing raceways. The vibration data in time and frequency domain is captured by FFT analyzer from an experimental setup. The time frequency domain conversion of a raw time domain data was carried out by wavelet packet transform, as it takes into account the transients and spectral frequencies. The rotor bearing model is simulated in ANSYS. Finally, most influencing statistical features were extracted by employing Principal Component Analysis, and fed to Multiclass Support Vector Machine. To train the algorithm, the simulated data is used whereas the data acquired from FFT analyzer is used for testing. It can be concluded that the defects are characterized by Ball Pass Frequency at inner race and outer raceway as indicated in the literature. The developed model is capable to monitor bearing's health which gives an average accuracy of 99%. [ABSTRACT FROM AUTHOR]

The remaining useful life (RUL) of the machine is one of the key information for predictive maintenance. If there is a lack of predictive maintenance strategy, it will increase the maintenance and breakdown costs of the machine. We apply transfer learning techniques to develop a new method that predicts the RUL of target data using degradation trends learned from complete bearing test data called source data. The training length of the model plays a crucial role in RUL prediction. First, the exponentially weighted moving average (EWMA) chart is used to identify the abnormal points of the bearing to determine the starting point of the model's training. Secondly, we propose transfer learning based on a bidirectional long and short‐term memory with attention mechanism (BiLSTMAM) model to estimate the RUL of the ball bearing. At the same time, the public data set is used to compare the estimation effect of the BiLSTMAM model with some published models. The BiLSTMAM model with the EWMA chart can achieve a score of 0.6702 for 11 target bearings. The accuracy of the RUL estimation ensures a reliable maintenance strategy to reduce unpredictable failures. [ABSTRACT FROM AUTHOR]

Copyright of Bearing is the property of Bearing Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Bearing is the property of Bearing Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Bearing is the property of Bearing Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Deep groove ball bearings are widely used in rotary machinery. Accurate for bearing faults diagnosis is essential for equipment maintenance. For common depth learning methods, the feature extraction of inverse time domain signal direction and the attention to key features are usually ignored. Based on the long short term memory(LSTM) network, this study proposes an attention-based highway bidirectional long short term memory (AHBi-LSTM) network for fault diagnosis based on the raw vibration signal. By increasing the Attention mechanism and Highway, the ability of the network to extract features is increased. The bidirectional LSTM network simultaneously extracts the raw vibration signal in positive and inverse time-domains to better extract the fault features. Six deep groove ball bearings with different health conditions were used to validate the AHBi-LSTM method in an experiment. The results showed that the accuracy of the proposed method for bearing fault diagnosis was over 98%, which was 8.66% higher than that of the LSTM model. The AHBi-LSTM model is also better than other relevant models for bearing fault diagnosis. [ABSTRACT FROM AUTHOR]

Precision spindle and bearings are the key components in precision machine tools. These structures greatly affect the machining accuracy and service life of the machine tools. In this paper, considering the uncertainty of rolling elements when the bearings are working at high speed, a new 2D equivalent simulation model of angular contact ball bearing was established based on the general finite element software, Abaqus. Meanwhile, the equivalent material parameters of virtual bearing ball in this 2D model were obtained via a standard bearing stiffness test and a parametric inversed method. The time to calculate of this model is reduced by 200 times compared with the 3D bearing simulation model. Then, the 2D equivalent simulation model of the spindle was established based on the 2D bearing model, which is used to calculate the axial stiffness and maximum contact stress between bearing balls and inner/outer rings in different assembly parameters. The results show that the stiffness of the spindle increases slowly at first, but then increases rapidly to a peak value after the bearing inner spacer sleeve is in contact with the bearing inner ring, and finally tends to stable, with the preload of the spindle continuing to increase. [ABSTRACT FROM AUTHOR]

The term "over-skidding" indicates that the cage rotational speed ratio exceeds the theoretical value as ball purely rolls on the raceway. Different from the skidding phenomenon that occurs in low-load and high-speed bearing, over-skidding usually occurs in large-size angular contact bearings, and it is still difficult to suppress under high load conditions. The main forms of damage to the raceway by over-skidding are spinning and gyro slip. To further explore the vibration characteristics and thermal effects of this phenomenon, a set of over-skidding tests of an angular contact bearing with a bore diameter of 220 mm were conducted on an industrial-size test bench. Through the experiment, the influence of axial load, rotational speed, and lubrication conditions on the occurrence of over-skidding were determined. Based on a previous dynamics model, the heat generation and thermal network models were integrated in the present study to predict the over-skidding and its thermal behavior. The model was validated in terms of the measured degree of over-skidding and temperature rise. The results showed that the degree of over-skidding reaches up to 12% of the theoretical value, and the friction power loss of the ball-pocket accounts for 30% of the total power loss. The analysis of the vibration signal showed a strong correlation between the bearing vibration characteristics and over-skidding behavior, thereby providing a way to indirectly measure the degree of over-skidding. [ABSTRACT FROM AUTHOR]

Power-electronic-converter-induced motor bearing currents are a widespread problem in the field of electrical drives. Parasitic capacitances between the electrical machine's parts provide a path for leakage currents, which finally harm metallic ball bearings. Remembering that end-windings have a significant contribution in building up stray capacitances, a countermeasure affecting both the lamination stack and end-winding areas is needed. This article focuses on a countermeasure against the noncirculating bearing currents in the cluster of solutions at the motor side. The electrostatic shielding approach, which is a known principle to reduce capacitive couplings, is applied in electrical machines every now and then. In this article, the principle of slot-embedded grounded electrodes is extended to cover also the end-windings. Thus, the electrodes provide a better shaft-to-ground voltage mitigating effect compared to the case where electrodes are applied only in the lamination stack area. The feasibility and effectiveness of such a countermeasure are investigated. Different options in terms of scaling of both the machine size and diameter of the electrodes were analyzed and corresponding conclusions were pointed out. [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]

This paper presents a mechanical model of angular contact ball bearing with local and extended defects in the outer raceway and the analytical formulations of varying stiffness under combined loads are obtained. The effects of radial load and clearance on variable stiffness of the bearing at the boundary positions are analyzed. Results show that the load distribution is not necessarily continuous and the maximum and minimum stiffness of the angular contact ball bearing can be located at either of the two boundary positions or even at non-boundary position under the effect of the contact angle. Meanwhile, the effects of defect depth and loads on the mechanical properties and varying stiffness of the bearing under localized and extended defects are studied, respectively, and the mechanism of "limit depth" and "critical load" is analyzed. These results are useful for quantitative fault diagnosis and reliability analysis of rotor-bearing systems. [ABSTRACT FROM AUTHOR]

Bearing misalignment may result in cage fractures and ball distribution errors. In order to analyze the effects of misalignments and ball distribution errors on the bearing stiffness fluctuation, considering the external loads and misalignments of inner and outer races, a quasi-static model of deep groove ball bearings with ball distribution errors is proposed. Based on the proposed model, the effects of ball distribution errors on the fluctuation characteristics of radial, axial and overturning stiffness of deep groove ball bearings under the condition of misaligned inner and outer races and external loads are further analyzed. The results show that the stiffness of the bearings fluctuates with the period of the ball passing through the outer race, that is, VC（variable compliance） vibration under the condition of the misaligned outer race and external loads. At this time, because of the existence of ball distribution errors, the bearing stiffness significantly fluctuates with the cage rotation period. The misalignments of the inner race rotating with the spindle cause the bearing stiffness to fluctuate by half of the inner race rotation period. The stiffness fluctuation amplitude increases due to the ball distribution errors. [ABSTRACT FROM AUTHOR]

To study the full sound field distribution characteristics of full ceramic ball bearings, reduce the radiation noise of the bearings, and improve their service performance. In this paper, the sound field distribution characteristics of 6206 silicon nitride ceramic deep groove ball bearings are studied under different oil supplies. A mathematical model of the sound field distribution of full ceramic ball bearings under oil lubrication is established, and the validity of the model is verified by experimental data. The bearing cavity simulation model of the full ceramic ball bearing is established, and the influence of oil supply on the operation characteristics of the full ceramic ball bearing is studied. Through theoretical and experimental research, the circular distribution law of the noise signal of ceramic ball bearings under different oil supplies is revealed. It is found that there is an optimal fuel supply when the speed and load are constant. Under optimal oil supply lubrication conditions, the full ceramic ball bearing has the minimum radiation noise, and the bearing exhibits optimal lubrication state, vibration and temperature rise characteristics. The new contribution of this paper: with the increase in oil supply, the sound pressure level of radiation noise of full ceramic ball bearings decreases and then increases. The research results reveal the radiation noise mechanism of full ceramic ball bearings, which is of great significance for enriching its theory and method. [ABSTRACT FROM AUTHOR]

Aiming to solve the problem of oil-air lubrication failure caused by the high working temperature of high-speed rolling bearings, this study proposes a method, based on the theory of gas-solid two-phase flow and bearing tribology, of predicting the dynamic temperature rise of nonlinear high-speed rolling bearings under oil-air lubrication conditions. The accuracy of the fluid–structure coupling model is verified by comparing the temperature rise test results of angular contact ball bearing at different speeds. The characteristics of oil-air lubrication circulation and the relationship between the lubrication parameters and the heat balance of the high-speed rolling bearings have been studied. The results show that the gas supply pressure of the system has a significant influence on the continuity and fluctuation of the oil film in the oil pipe nozzle. The initial rise in temperature of the inner and outer rings of the bearing and the fluid domain has a speed threshold value, and the temperature increases linearly with the bearing speed. With the increase in the oil supply and lube oil viscosity of the system, the temperature rise of the outer ring of the bearing increases first, then decreases, and finally increases again. There is an optimal oil supply 5.5 mL and optimize viscosity 68 cSt for the bearing in the work condition. [ABSTRACT FROM AUTHOR]

Grease-lubricated rolling element bearings can suffer from wear due to lubricant starvation under certain oscillating operating conditions. Especially for large-scale slewing bearings, such as blade bearings in wind turbines, experimental investigations are complex compared to small-scale reference testing. For an easier manner of testing, it is desirable to know whether the results of small-scale testing are applicable to larger-sized bearings. In this work, three different bearing types were tested and compared to already published results from a small-scale ACBB with a pitch diameter of 60 mm. The newly tested bearing types comprise a downscaled blade bearing (4-point contact double row ball bearing) with a pitch diameter of 673 mm, a small-scale CRTB with a pitch diameter of 77.5 mm and another ACBB with a pitch diameter of 95 mm. Qualitatively, all tested bearings show similar wear behaviour in terms of friction energy when operation parameters are varied. With higher oscillation frequency, damage becomes more severe. The oscillation amplitude shows three distinctive regimes. Within the range of small amplitudes, an increase in amplitude leads to more pronounced damage. We observe a threshold amplitude where this is no longer the case; a further increase in amplitude counteracts wear initiation until a final threshold is reached, beyond which no more wear is observed. These findings are in accordance with the reference results of the small-scale ACBB. Direct comparison between point and line contact shows that the latter is more prone to wear initiation under grease-lubricated, oscillating operating conditions. Furthermore, a previously introduced empirical number shows good performance in assessing critical operating parameters of the different bearing types. Specifically, harmful operating conditions can be classified for all studied bearing types with an accuracy of 78%. This method can be useful to assess operating conditions of greased, oscillating, rolling element bearings, e.g., to assess different pitch controllers or designs of slewing bearings. [ABSTRACT FROM AUTHOR]

Rotor blade bearings enable rotor blades to pivot about their longitudinal axis and thus control the power output and reduce the loads acting on the wind turbine. Over a design period of 20 years, rolling bearings are exposed to frequent oscillation movements with amplitude ratios of x / 2 b > 1, especially due to new control concepts such as Individual Pitch Control, which can lead to wear and a reduction in service life. The objective of this paper was to identify the dominant wear mechanisms and their consequences for the operation of oscillating bearings. Oscillating experiments with an increasing number of cycles on the angular contact ball bearings of two different sizes (types 7208 and 7220) show that the damage initiation starts with adhesive and corrosive wear mechanisms, which result in a sharp increase in the torque as well as the wear volume on the bearing raceway. As the number of cycles increases, an abrasive mechanism occurs, resulting in a lower slope of the wear curve and a smoothing of the resulting wear depressions. The wear and torque curves were evaluated and classified using an energy-wear approach according to Fouvry. [ABSTRACT FROM AUTHOR]

The complex sliding behavior inside ball bearings seriously affects the mechanical system's performance. Current dynamic models for predicting this behavior suffer from poor generality and convergence. To address this issue, different interactions between the ball and raceway are proposed in this paper to simulate the dynamic behavior by analyzing the bearing assemblies' motion features under typical operating conditions. The number of variables and equations to be solved is determined adaptively according to the bearing load characteristics, thus improving the efficiency and convergence of the model solution. The good agreement between simulation results and experimental test results validates the reliability of the model. The sliding behavior at the ball/raceway interface under different conditions is further investigated. The results show that the heavy external loads can avoid severe sliding at the interface but shorten the bearing's fatigue. When the bearing is subjected to combined load conditions, the increased radial force inhibits bearing sliding while increasing the non-uniformity of the sliding velocity distribution. [ABSTRACT FROM AUTHOR]

Copyright of Lubrication Engineering (0254-0150) is the property of Editorial Office of LUBRICATION ENGINEERING and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

False brinelling is a type of fretting wear that occurs in rolling bearings when the contacts of bearing rings and rolling elements are subjected to small-amplitude oscillatory motion. It manifests itself as deep craters with relatively polished bottoms that are evenly spaced around the bearing rings. This work investigates the influence of lubricant properties and contact conditions, including oil viscosity, applied load, and amplitude and frequency of oscillations, on the onset and progression of false brinelling damage. Experiments were conducted with AISI 52100 bearing steel specimens in a ball-on-flat configuration under small-amplitude oscillating conditions. A set of base oils and a group of custom-made greases with systematically varying properties were employed. Importantly, the same ball-on-flat setup was adapted to allow optical access to the contact by employing a sapphire disc instead of a steel one. This allowed direct observation of the damage onset and progression to better elucidate the mechanisms taking place. Additional experiments were conducted with the same lubricants on a thrust ball bearing rig and the observed trends were compared to those from the ball-on-disc setup. Results show that false brinelling damage initiates locally at discrete asperity microcontacts and then spreads relatively quickly with continued rubbing to cover the whole contact area. Oscillation amplitudes shorter than the Hertz contact width (A/D < 1) were shown to be most damaging, while the damage reduces drastically for amplitudes larger than the Hertz contact width (A/D > 1). For the more important case of A/D < 1, oils and greases with lower viscosities produced less damage. Oils in general produced somewhat less damage than the equivalent lithium- or urea-thickened greases with the same base oil. Lower oscillation frequencies and lower contact pressures also produced less damage. The corresponding friction and electrical contact resistance measurements indicate that under these conditions of A/D < 1 the contact operates under boundary lubrication at best but can intermittently approach effectively dry conditions, depending on lubricant properties and applied conditions. These observations indicate that the key variable that controls damage when the oscillation amplitude is less than the contact width is the ability of the lubricant to penetrate and remain in the oscillating contact. Therefore, lubricant properties and contact conditions that promote this penetration, which may be different from those that promote hydrodynamic film formation, can mitigate against false brinelling. [ABSTRACT FROM AUTHOR]

Ball bearing turbochargers (TCs) incorporate an angular contact ball bearing cartridge to reduce friction and oil consumption, improving the efficiency of internal combustion engines. In this investigation, axial and radial TC rotor motion was experimentally measured and used to develop a model of the TC rotor-bearing system, allowing for a detailed analysis of the TC bearing under varying operating conditions. In order to achieve the experimental objectives of this investigation, eddy-current proximity probes were used to measure the radial motion at the turbine and compressor sides of the TC. The measured radial motion shows whirl with subharmonics at low speed. The measured axial motion of the rotor was found to increase with TC speed. In order to analytically investigate the bearing dynamics, a complete TC model was developed that includes the mass distribution and flexibility of the TC compressor, shaft and turbine, and squeeze-film dampers (SFDs) that support the bearing cartridge. The model was used to replicate the whirl and axial motion of the test rig and then to determine which model parameters could be adjusted to minimize whirl without negatively affecting the bearing dynamics. Simulation results revealed that centrifugal effects cause a change in the bearing internal geometry, with a small clearance becoming a preload at higher speeds. When this effect is coupled with less compliant SFDs, the subharmonics are reduced and the overall sliding and number of large load cycles at the ball–race contacts are minimized, contributing to lower bearing friction and improved overall life. [ABSTRACT FROM AUTHOR]

Spherical roller bearings (SRBs) are widely used under self-aligning operating conditions, such as rotor bending or an angular misalignment between inner and outer rings due to their self-aligning function. However, the characterization of SRBs' self-aligning function is often ignored in the present models. The reason for this is that the self-aligning condition is essentially a fault condition, and many scholars have assumed SRBs are in an ideal operating condition. Although there is nothing wrong with this analysis theoretically, it is incapable of characterizing SRBs' service behavior comprehensively. In this work, the Lagrange equation was introduced to model the relationship among the rollers and the inner and outer rings. The contact region in particular was characterized in detail in order to solve the problems of undetermined contact status (UCS) and the varying law of the self-aligning contact angle (SAC angle). For the experiment, a novel SRBs pedestal with a self-aligning operating condition was designed, and the relevant self-aligning function testing was carried out. A good agreement was shown between the theoretical and experimental results. The results pointed out that, if taking no account of the self-aligning function, SRBs can be regarded as angular contact ball bearings or cylinder roller bearings. The amplitude of the inner-ring motion orbit is determined by the external load, but the shape is influenced by the direction and magnitude of the SAC angle. In the example of this paper, the values of the main frequency equal 136.8 Hz. Some additional frequencies are clearly aroused under the self-aligning operating condition, whose value is approximately equal to 8.3 Hz or its integer multiples. The dynamic performance of SRBs will be substantially improved by a light axial load plus an anticlockwise self-aligning contact angle rather than a large axial preload. [ABSTRACT FROM AUTHOR]

In this paper, the nonlinear dynamic response of deep groove ball bearings with clearance was studied numerically. The imperfect connections with the clearance of raceways and rolling balls were established by the contact elements. In order to describe the contact characteristics accurately, a hysteresis damping coefficient was introduced into the Hertz contact model, which represented the dissipative term during the contact–impact process. The tangential force of the contact bodies was obtained based on a modified Coulomb friction model. Then, the dynamic analysis model of the deep groove ball bearings with clearance was built. Meanwhile, the experimental test platform of the deep groove ball bearings with various operation conditions was built and the dynamic simulation was utilized as the demonstrative case to conduct the investigation. The numerical results revealed that the existence of clearance would change the motion trajectory of a rolling ball and the appearance of the different movement states (free, contact, and penetration). In addition, the contact characteristics and sliding features would be changed with the variations in the operation conditions and structural characteristics. [ABSTRACT FROM AUTHOR]

The ability of bearings to resist oil interruption directly affects the reliability of aero engines. In order to explore the dry operation performance of a novel cageless angular contact ball bearing， an oil break test scheme under the bearing ring is designed， and a test platform and an operation program are constructed. The changes of bearing appearance， temperature， speed and current after oil cut off are analyzed. The results show that the dry running time of the new type of bearings is 51 min under high rotation speed and high axial load. It proves that the new type of bearings has good anti-oil interruption ability， and can be widely used in industry.

Bearing is an important machinery part in industry. When bearings fail to meet their expected life, the consequences are increased down time, loss of revenue and missed delivery. This article describes the failure of a gear box bearing in rolling contact fatigue. The investigation consists of visual observation, chemical analysis, characterization of microstructures using optical microscopes and hardness test. The present study also considers bearing life as well as operational condition of bearings. Surface-initiated rolling contact fatigue, leading to a surface failure known as pitting, is a life-limiting failure mode in many modern machine elements, particularly rolling element bearings. Metallography analysis of crack propagation and crack morphology was also described. Indication of fatigue spalling in ferrography test was also discussed. Analysis suggested the probable reasons of such kind of failure in operation. [ABSTRACT FROM AUTHOR]

A transient mixed thermal elastohydrodynamic lubrication model of bearing considering the thermal effect and the changes in velocity, load, and contact geometry is proposed. Based on the bearing dynamic and lubrication analysis, the effects of bearing rotational speed and start-stop conditions on the dynamic behavior and lubrication performance are studied. Results show that when the bearing rotational speed exceeds a certain critical value, the increasing speed will reduce the film thickness, especially the outer raceway. The increasing bearing acceleration can cause a higher slide-roll ratio and film temperature at the initial start-up process. Compared with the start-up process, the lubrication change in the shut-down process has a similar opposite trend, but the overall lubrication performance is better. [ABSTRACT FROM AUTHOR]

Dynamic characteristics of ball bearings with different cage pocket shapes are investigated with consideration to the concurrent rotation of the inner and outer rings. Contact models of balls with cylindrical, elongated cylindrical, and rectangular pockets are established. The ball excursion, cage trajectory, contact force, and cage speed are analyzed. The results show that the elongated cylindrical pocket leads to a more stable trajectory of the cage since balls always impact the leading side of the pocket. However, for the cylindrical and rectangular cage pockets, both the leading and trailing sides of the pockets are randomly impacted by balls, which may cause chaotic motions of the cage. [ABSTRACT FROM AUTHOR]

• An analytical method for the dual-rotor-disc-bearing coupled system in aero-engine is developed. • The coupling relationship between the rotor system and the bearing support system is established. • The running state of the system is closely related to the speed and unbalanced mass distribution. • There is a certain speed range where the system stability is reduced and a reverse zone appears of bearing contact direction. • The analytical model is confirmed using the FE method and experimental testing. This paper introduces a mathematical method for the flexible dual-rotor-disc-bearing coupled system in aeroengines. Through meticulous simulation and experimental observation, the impact of the unbalanced disc on the response characteristic and interference relation of rotor systems is investigated. Beyond the general focus on the dynamic behavior, the discussion delves into uncovering the generation mechanism of the coupling relationship and the intricate process of vibration transmission between the rotor system and the bearing support structure. The investigation reveals that during system operation, significant bending-torsional coupled deformation of the rotor will be generated, with each node exhibiting three-dimensional movement. When the angular velocities of the two rotors approach similarity, the beating vibration phenomenon becomes observable. The node trajectory exhibits a petal-shaped pattern, with the number of petals corresponding to the sum of peaks and troughs of the response curve within one period. During the low-speed phase, the unbalance mass of the inner disc predominantly excites the system, whereas in the high-speed phase, the unbalance mass of the outer disc substantially contributes to system vibration. Under transitional conditions, the system's motion stability is diminished, the contacting process between bearing balls and rings is disrupted, and a reversing zone emerges in the contact direction. [ABSTRACT FROM AUTHOR]

In high-speed ball bearings, the revolution of spherical elements is significantly influenced by drag force of lubricant fluid, impacting the bearing's dynamic and thermal performance. To investigate drag force in under-race lubrication ball bearings, a numerical study was conducted after the experimental verification. A multi-sphere flow model with a sandwich plate was tested, which indicates a strong agreement between numerical calculations and experimental data, with an error margin below 10 %. In the numerical simulation, pressure distribution and shear stress on the ball was studied, considering variables such as bearing rotational speed, oil flow rate, oil density, and oil viscosity. Results reveal low pressure at the upper hemisphere's center and high pressure on both sides. Shear stress is concentrated in contact areas between the element and components like the inner ring, outer ring, and cage. Oil injection from the inner ring significantly alters the pressure and shear stress distribution in the lower hemisphere. The direction of drag force is the same as the rolling element's revolution, acting as driving force for elements' revolution. Increasing bearing rotating speed, oil flow rate, oil viscosity, and oil density all contribute to higher drag forces on the ball. Based on the numerical simulations, a predictive formula for the ball's drag force was developed. [ABSTRACT FROM AUTHOR]

• A dynamic model for a shell-propulsion shaft system is proposed. • The shell flexibilities are considering based on Kirchhoff-Love shell theory. • The results with and without considering shell flexibility are compared. • Experimental validation is conducted to prove the correctness of the dynamic model. The shell flexible deformation will affect the dynamics of the shell-propulsion shaft system. Most previous studies were only focused on the dynamics of flexible shaft systems. Few studies considered the flexible deformations of the shell. This work presents a shell-propulsion shaft system dynamic model considering the shell and shaft flexibilities. The shell-propulsion shaft system in this work consists of one propeller, one shaft, one conical shell, one four-point contact bearing, and one deep groove ball bearing. The shaft dynamic model is established based on Timoshenko beam theory. The conical shell dynamic model is established based on the Kirchhoff-Love shell theory. The propeller and bearing dynamic models are given by using the lumped parameter method. The proposed shell dynamic model is compared with the finite element method (FEM). An experimental validation is conducted to prove the correctness of the propulsion shaft dynamic modeling method. The results obtained by the models with and without considering the shell flexibility are compared. Finally, the effect of the eccentricity error on the shaft and shell vibrations is analyzed. [ABSTRACT FROM AUTHOR]

Multi-point contact often occurs between the balls and raceways of the four-point contact ball bearing (FPCBB) due to operating conditions and manufacturing errors, which can lead to unstable motion and wear of the cage. A dynamic analysis method for FPCBB with a flexible cage under multi-point contact is presented in this paper. Initially, the boundary conditions for different contact points (two-point, three-point, and four-point contact) are clarified through the research of the dynamic interaction and collision mechanisms between the balls and the raceways. Subsequently, based on the structure flexibility, and the collision effect among the balls, cage, and guiding ring, a dynamic model for FPCBB is constructed, and the heightened accuracy and superiority of the model are substantiated through comparative analyses with the conventional rigid cage model. Furthermore, the influence of operating conditions and manufacturing errors on the rotational stability and the wear degree of the cage are explored, and the accuracy and reliability of the model are experimentally verified. The results show that the degree of cage wear is strongly influenced by the contact state, and the maximum wear degree varies at different positions. Reasonable speeds, loads, and manufacturing error range can effectively improve the contact conditions, thereby augmenting cage motion stability and mitigating wear. This research contributes novel insights into the failure analysis and structural optimization of the FPCBB. [ABSTRACT FROM AUTHOR]

To improve the tribodynamic performance of ball bearings, micro-texturing has been widely used on bearing components and significant beneficial effects by using different shape, size and density of dimples at their contact zone has been reported in literature. However, behaviour of textures in vicinity of the contact zone in machine components particularly in ball bearings, where lubricant/grease is push aside from the contact zone has not been explored yet. Hence, two different configurations of micro-textured inner races (i.e., inner races with large number of circular micro-dimples circumferentially on both sides of the central non-textured zones of 2.2 and 1.0 mm) of a deep groove ball bearing have been fabricated by employing a low power laser marking machine. The performance of these micro-textured bearings (MTBs) possessing textured inner races and conventional outer race have been evaluated by conducting experiments in a test rig designed and fabricated inhouse. Capacitance based electrical method, load sensor, thermocouple and miniature type accelerometer have been employed for measuring film thickness, frictional torque, temperature rise and vibrations respectively at realistic bearing loads (speed: 1.4–5.6 m/s, and loads: p H =1.07–1.70 GPa) and the results were compared with that of a same size conventional bearing (SKF: BB1B 420 206). About 8–27 % improvement in film formation, reductions in overall vibration level (5–36 %), frictional torque (10–35 %) and bulk temperature rise (14–37 %) has been recorded in case of MTBs as compared to the conventional bearing (CB) cases at identical load conditions. Moreover, study on the effect of the positioning of the textures with respect to the contact zone on performance behavior of bearings indicated that the tribological and vibration behavior of MTB-2 (bearing with a micro-textured inner race where, textures were created in vicinity of 1.0 mm central non-textured zone) is better than that of the MTB-1 (bearing with a micro-textured inner race, where textures were created in vicinity of 2.2 mm central non-textured zone) and CB at tested loads and speed range. [ABSTRACT FROM AUTHOR]

The paper introduces a dynamic model of the bearing-rotor system covering four-point contact ball bearings (FPCBB) and cylindrical roller bearings (CRB), specifically tailored for offshore wind applications. The slice method is well addressed the non-uniform contact between the rollers and other components. The semi-flexible body element strikes an optimal balance among rotor flexibility, real-time coupling, and simultaneous solution of the bearing and rotor models. The differences between the rigid and flexible models in predicting the system behavior are compared. The effect of the bearing clearance on its dynamic performance is further investigated. The results show that the flexible model is capable of predicting stress concentrations in the CRB raceways with a stress error of 12% compared to the rigid model. The occurrence of multi-point contact state inside FPCBB is predicted by the flexible model. The CRB clearance has a more significant effect on the system dynamic performance. And the wider the CRB clearance, the more pronounced the sliding inside the raceway of the right CRB, which can reach an alarming velocity of 18 m s−1. These findings offer valuable insights for the modeling and performance optimization of bearing-rotor systems in offshore wind turbine gearboxes, ensuring enhanced reliability in demanding ocean environments. • A new dynamic model of the bearing-rotor system, covering CRBs and FPCBB, was presented. • The differences between the rigid and flexible models in predicting the system behavior are compared. • The rotor bending deformation under external forces results in stress concentrations in CRB raceway. • The CRB clearance has a greater impact on dynamic performance than that of the FPCBB. [ABSTRACT FROM AUTHOR]

The case dependency of vibration-based Structural Damage Detection (SDD) models on their training structure (data) has always been a setback in their application to new structures with no or limited data. Obtaining labeled data for both non-damage and damage conditions is an expensive and time-consuming process, which is nearly impractical for operational buildings. For Fault Detection (FD) methods in rotating machines, the rotating parts (e.g. , ball bearings) are the monitoring targets. The parts used in FD are less complex pieces to deal with in the laboratory environment, and various damage scenarios can be applied to them in a relatively feasible way. From a Deep Learning (DL) perspective, given the similarity of FD and SDD problems, this study aims to leverage Transfer Learning (TL) across rotating machines and framed structures as the source and target domains, respectively. The TL model must be in a zero-shot setting; otherwise, labeled data is needed for the target structure damage condition. This study uses a unique Domain Adaptation algorithm and a Contrastive Learning (CL) approach that is explicitly designed for performing TL between (rotating machines) FD and (framed structure) SDD tasks. A rotating machine benchmark dataset with over 45 data cases is used to test the proposed methodology, and various CL models are trained across its non-damage and damage conditions. The accumulated knowledge is then applied to two SDD benchmarks for framed structures, the Yellow Frame (YF) and Qatar University Grandstand Simulator (QUGS), through a weighted deep ensemble strategy across the CL models. The method is successfully tested on target structures, and two comparisons are made with a competitive zero-shot Autoencoder(AE)-based model, as well as with the supervised performance, which has access to the target framed structures' damage data. The objective is to surpass the AE-based SDD model performance by leveraging the FD knowledge gained from the rotating machine data and evaluating how close it can get to the supervised performance. On average, the mean F1 score across various damage condition cases is 0.963 and 0.989 for the YF and QUGS, respectively, while the corresponding numbers for the AE-based and supervised models are 0.844 and 0.974 for YF and 0.940 and 0.998 for the QUGS, respectively. In conclusion, the methodology presented in this paper opens a new SDD venue, enabling TL operations among rotating machines and framed structures. Data and codes are available at https://github.com/Hesam-92-19/Machine_To_Structure_TL. [ABSTRACT FROM AUTHOR]

Bearing misalignments are common defects in machinery. One of the most important types of that is the angular misalignment of the bearing rings. In this study, crookedness specific signature related to thrust ball bearing shaft washer is investigated. For this purpose, a vertical structural thrust ball bearing test rig was considered. In the following, effects of rotational shaft speed, crookedness value and axial external force on the shaft washer crookedness signature were studied at several relative positions of sensors. It is shown that crookedness of thrust ball bearing shaft washer has specific frequency and sensor phase difference pattern in the nonlinear vibration responses. Also, the experimental results are applied to validate results of a 4-dof nonlinear dynamical system related to the shaft washer crookedness of thrust ball bearing. In the next step, by comparing input and output amplitude and also existence of flip bifurcation, it is illustrated that this system is a nonlinear dynamical experimental system. It was shown that this nonlinearity makes crooked shaft washer pattern difficult to identify. Finally, by the phase portrait of the sensor response and the relative error value of crookedness signature frequencies, it is clear that the crookedness of shaft washer creates quasi-chaotic behavior supporting crookedness signature frequencies and phase pattern as a supplement property. • A vertical structural thrust ball bearing test rig was considered. • Introduction of novel detection pattern for thrust ball bearing shaft washer crookedness. • Validation of the results of a 4-dof nonlinear dynamical system by the results of experimental test rig. • Application of Poincare map to create a novel supplement method to detect crookedness of thrust ball bearing shaft washer. [ABSTRACT FROM AUTHOR]

The accuracy of the vibration response in a defective bearing dynamics model depends on the precise representation of the lubrication friction state between the rolling element (RE) and the raceway within the model. In this study, a fault dynamic model for outer ring defect of deep groove ball bearings (DGBBs), considering the lubrication state transition in a thermal environment, is established. This model accounts for the asperity contact effect during the lubrication state transition and integrates the lubrication-friction model for temperature changes into the dynamic model when skidding occurs. The influence of lubrication state change on the fault frequency of outer ring of DGBB in thermal environment is studied. The experimental and simulation results indicate that the lubrication state of the bearing is gradually deteriorated from elastohydrodynamic lubrication to mixed lubrication with the increase of working temperature. The transformation of the lubrication state is shown to have a significant effect on friction, resulting in the fault frequency of the outer ring increasing with temperature, which exhibits substantial deviation in the thermal environment. In the temperature range of 30 °C–150 °C, the deviation of defect frequency reaches 15.5%, which affects the accuracy of bearing fault diagnosis. This study may offer recommendations for enhancing the condition monitoring of rolling bearings under extreme working conditions. • The asperity contact effect between rolling element (RE) and raceway is considered to improve the accuracy of the system. • The lubrication state of bearing deteriorates as temperature rises, resulting in a decrease and then an increase in friction. • The nonlinear change of friction affects the speed of RE and cage, and the dynamic behaviors of bearing change significantly. • The change of cage speed modulates the outer ring fault frequency of bearing, which causes an obvious frequency deviation. [ABSTRACT FROM AUTHOR]

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Copyright of Journal of Henan University of Science & Technology, Natural Science is the property of Editorial Office of Journal of Henan University of Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The article presents an adaptation of a parametric diagnostic method based on the square of the amplitude gains model, which was tested in experimental studies on bearing damage detection (outer race, inner race, bearing balls damage). The described method is based on the shaft displacement signal analysis, which is affected by vibrations coming from the bearings. The diagnostic model's parameters are determined by processing the signal from the time domain to the frequency domain in a few steps. Firstly, the recorded signal is divided into two observation periods, next the analytical autocorrelation functions are determined and approximated by a polynomial. Then, the diagnostic thresholds are adopted, and the model parameters are converted into damage maps that are easy to interpret and assess the technical condition of the bearings. The presented method shows the technical condition of bearings in a qualitative way. Depending on the received color damage maps, it is possible to determine their level of wear. Green and blue indicate poor wear or no damage, red indicates increased wear, and black clearly indicates a damaged bearing. [ABSTRACT FROM AUTHOR]

The stiffness and fatigue life of deep groove ball bearings are greatly affected by interference fits, preloads and tilting moments. Up to now, most of current works failed to focus on the integrated analysis of stiffness and fatigue life, especially the off-diagonal stiffness items in the bearing stiffness matrix. This paper proposed an improved mathematical model of deep groove ball bearings with the consideration of interference fits and tilting moments. On this basis, the combined study on stiffness and fatigue life is conducted to determine the optimal match of interference fits, preloads and tilting moments. Moreover, the variations in off-diagonal stiffness items under different interference fits, preloads and tilting moments are also given. These results are beneficial for the assembly of deep groove ball bearings to obtain the best stiffness and fatigue life. Also, the sensitivity of off-diagonal stiffness items to interference fits, preloads and tilting moments is demonstrated, which greatly affects the dynamic characteristic of ball bearings. [ABSTRACT FROM AUTHOR]

Bearings are the most commonly used components in rotating machines and the ability to diagnose their faults and predict their remaining useful life (RUL) is critical for system maintenance. This paper proposes a smart system combined with a regression model to predict the RUL of bearings. The method converts the azimuth signal through low-pass filtering (LPF) and a chaotic mapping system, and uses Euclidean feature values (EFVs) to extract features in order to construct useful health indicators (HIs). In fault detection, the iterative cumulative moving average (ICMA) is used to smooth the HIs, and the Euclidean norm is used to find the time-to-start prediction (TSP). In terms of prediction, this paper uses a self-selective regression model to select the most suitable regression model to predict the RUL of the bearing. The dataset provided by the Center for Intelligent Maintenance Systems (IMS) is applied for performance evaluation; in comparison with previous research, better prediction results can be achieved by applying the proposed smart assessment system. The proposed system is also applied to the PRONOSTIA (also called FEMTO-ST) bearing dataset in this paper, demonstrating that acceptable prediction performance can be obtained. [ABSTRACT FROM AUTHOR]

Oil lubrication is widely adopted in rolling bearings, the characteristics of which affect the oil film formation and friction state, and also the heat generation and dissipation characteristics. However, it is difficult to measure the internal lubrication of rolling bearings in practice, which is of great importance for lubrication and structure design. In this work, one measurement system for lubricant distribution was built and installed on a test rig to obtain original pictures of the lubricant in bearings. Grayscale images were obtained by picture processing to characterize the lubricant distribution, and the image pixels were evaluated for the characterization of lubricant volume. Finally, the measurement of the lubricant distribution in the angular ball bearing was carried out under different lubrication and cage groove conditions, and their influences were investigated. The results show that the lubricant distribution is affected by the oil jet nozzle angle, operating speed, and cage structure. The lubricant capacity among balls and the cage pocket in bearings gradually increased with the increase in the nozzle angle and the depth of the cage grooves, but decreased with the increasing operating speed. The experimental results are helpful to provide a basis for the structure and lubrication design of ball bearings. [ABSTRACT FROM AUTHOR]

To study the variation rules of nonlinear stiffness of double-row angular contact ball bearings (DR-ACBB), this paper proposed a general mathematic model for DR-ACBB under three different configurations based on the improved quasi-static model of ball bearings, an explicit expression stiffness matrix of DR-ACBB is analytically derived, and a double-layer nested iterative algorithm based on the Newton–Raphson method is designed to realize the efficient solution of the proposed model. Then, the effects of the preload, speeds, and loads on the nonlinear stiffness variations of DR-ACBB under different arrangements are comparatively analyzed. The results show that DR-ACBB under the DB and DF configurations have the same variation rule in axial and radial stiffness; that is, a nonlinear soft-spring stiffness characteristic (i.e., the stiffness decreases with the external load) within the low-speed range and light load condition, and a nonlinear hard spring stiffness characteristic (i.e., the stiffness increases with the external load) within the high-speed range or heavy load condition. [ABSTRACT FROM AUTHOR]

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Copyright of Lubrication Engineering (0254-0150) is the property of Editorial Office of LUBRICATION ENGINEERING and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)