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

In this paper, finite element simulation of asymmetric rolling in relief rolls of C11000 copper alloy in order to analyze the effectiveness of possible roll profiles and technological schemes of deformation was performed. The scientific innovation of this work lies in determining the patterns of development of stress-strain state parameters for various configurations of rolls, as well as determining the effectiveness of metal processing using various technological schemes. It was found that the use of trapezoidal relief makes it possible to increase the level of metal processing by almost 5 times compared with the use of radial relief. Comparison of technological schemes of deformation showed that deformation with 180° workpiece turning between passes significantly reduces the influence of the asymmetry factor. Deformation without changing the workpiece position between the passes has the opposite effect, and such a scheme significantly increases the influence of the asymmetry factor. Deformation with a transverse workpiece shift for the relief period between passes has the effect of a "golden mean." The conducted laboratory experiment for lead billet showed that the shape change of lead billet during computer simulation has a high level of convergence with real conditions. At each stage of deformation, the difference in the geometric parameters of the workpiece between the model and the experiment did not exceed 3-5%. When deforming a copper billet, the maximum difference level was 8%, which is the result of the low rigidity of the rolling cage with smooth rolls. [ABSTRACT FROM AUTHOR]

With the rapid development of railway towards being high speed and having heavy load capacity, the wheel–rail wear and rolling contact fatigue in the curve section with a small radius of freight have become the key problems in urban railways, which need to be solved urgently. The aims of this study were to compare the wear resistance with three different lubricating conditions on wheel–rail wear based on the wheel–rail rolling contact simulation tests. The wear loss, microhardness, and microstructure of the contacted surface of the rail were detected systematically. The results showed that the wear rates of rail were reduced by 71% for grease lubrication and 55% for solid lubrication, compared to those without lubrication. At the same time, the thickness of plastic deformation layer of rail samples were about 167 μm for the dry state, 138 μm for the solid lubrication state, and 128 μm for the oil lubrication state, respectively. It indicates that the thickness of the plastic deformation layer was significantly reduced under both grease and/or solid lubricating conditions. In addition, the microstructure of the deformation layer with two kinds of lubricated states was coarser and denser than that without lubricants. The average grain size of the deformation layer was approximately 0.22 μm under dry conditions and 0.32 μm under lubricated conditions. It also indicated that the changes in lubricants did not have a significant effect on the average grain size of the deformation layer. The results of the present study could provide theoretical reference for the development and design of lubricants used as rail materials. [ABSTRACT FROM AUTHOR]

Currently, mechanical gears with cycloid engagement are increasingly used in mechanisms along with involute ones. In modern drive mechanisms, using pin gears and gears with intermediate rolling elements (IRE) is widespread, which simultaneously use cycloid gears. To a greater extent, pin gears are now being investigated, but IRE gears have their undeniable advantages. Many works are devoted to the study of cycloid toothing for certain gears, but the efficiency, especially that of IRE gears, has practically not been investigated. Therefore, the analysis of power losses in the engagement of a gear with IRE and a free cage (IREFC) is relevant. In this analysis, the authors of the work have used laws of mechanics, methods of energy flows and a secant normal. Mathematical expressions have been obtained to estimate slip speeds and power friction losses in the engagement of a gear with IREFC, and a formula has been derived to determine the efficiency of a mentioned mechanical transmission. The calculation of slip speeds and power losses at the points of contact of a rolling element with cycloid profiles of wheels for selected initial parameters of a gear with IREFC has been presented. The friction power and the overall efficiency of the entire gear engagement have also been calculated. This work shows that power friction losses at the points of contact of a rolling element with cycloid profiles of tooth wheels of a gear with IREFC are not the same. The friction power in the contact of a rolling element with a cycloid profile of a cam is an order of magnitude higher than the friction power in the contact of a rolling element with a cycloid profile of a crown. [ABSTRACT FROM AUTHOR]

In current railway rails, trains are propelled by the rolling contact between iron wheels and iron rails, and the high frequency of train repetition on rails results in a significant load exertion on a very small area where the wheel and rail come into contact. Furthermore, a contact stress beyond the allowable stress of the rail may lead to cracks due to plastic deformation. The railway rail, which is the primary contact surface between the wheel and the rail, is prone to rolling contact fatigue cracks. Therefore, a thorough inspection and diagnosis of the condition of the cracks is necessary to prevent fracture. The Detailed Guideline on the Performance Evaluation of Track Facilities in South Korea specifies the detailed requirements for the methods and procedures for conducting track performance evaluations. However, diagnosing rail surface damage and determining the severity solely rely on visual inspection, which depends on the qualitative evaluation and subjective judgment of the inspector. Against this backdrop, rail surface defect detection was investigated using Fast R-CNN in this study. To test the feasibility of the model, we constructed a dataset of rail surface defect images. Through field investigation, 1300 images of rail surface defects were obtained. Aged rails collected from the field were processed, and 1300 images of internal defects were generated through SEM testing; therefore, a total of 1300 pieces of learning data were constructed. The detection results indicated that the mean average precision was 94.9%. The Fast R-CNN exhibited high efficiency in detecting rail surface defects, and it demonstrated a superior recognition performance compared with other algorithms. [ABSTRACT FROM AUTHOR]

The roller–shoe mechanism is a classic mechanical assembly with an essential role in motion transmission. Common rail high-pressure pumps are an example of a complex assembly that uses such a mechanism to transform the rotation motion into a translation one. The rolling element of the mechanism is represented by a cylindrical roller. Although it can carry heavy loads due to its design, a proper surface profile could significantly increase the life of the entire mechanism. A better solution can be achieved using a logarithmic profile. The shoe is the second base element of the mechanism. It is a part with an inner cylindrical surface and it is separated from the roller by a thin lubricant film. Considering this, increasing the hardness of the roller–shoe contact surface can be obtained using a suitable coating. The positive results of this coating are highlighted using endurance tests to which high-pressure pumps are subjected. Therefore, the roller profile and the shoe coating represent two directions for improving the contact between the mechanism transmission elements, in terms of wear reduction. The purpose of this paper is to identify a suitable roller profile and to highlight its impact on the shoe coating. [ABSTRACT FROM AUTHOR]

This article discusses the behavior of lubricated bearings in electric circuits, which has become increasingly important due to the growing electrification of individual mobility and renewable energy technologies. The research work in this field is predominantly published in German, so this special issue aims to provide a comprehensive overview of the topic. The article explores various models and methods for analyzing the electrical impedance behavior of rolling and plain bearings, as well as the potential for using bearings as integrated sensors in industrial processes. The challenges and potential applications of using electrical properties of bearings for damage detection and predictive maintenance are also discussed. The special issue includes several research papers that cover different aspects of this topic, including electrical bearing currents, lubricant film conditions, surface topology, strain measurement, and the factors influencing bearing currents. The authors express their gratitude to the contributors and reviewers for their valuable contributions. [Extracted from the article]

Railway systems play a pivotal role in modern transportation networks, contributing to both efficiency and environmental sustainability. This study investigated the multifaceted aspects of wear phenomena in railway engineering, focusing on their significant implications for environmental costs and operational efficiency. Experimental trials were conducted using a high-performance bi-disc apparatus, evaluating a range of materials, contact pressures, and lubrication conditions. Shakedown maps were employed to assess ratcheting behaviour, while the wear rate was analysed as a function of the fatigue index (FI). The results reveal the intricate interplay of contact pressure, slip ratio, material properties, and lubrication in determining wear and ratcheting behaviour. Oxidative and mild wear mechanisms were identified, and wear debris composition and morphology were characterised. The outcomes from this research clarify the pivotal role that wear processes play within railway systems and the far-reaching environmental repercussions they entail. This exploration contributes to the ongoing optimisation of railway operations, offering valuable insights aimed at mitigating unavoidable pollution sources and strengthening sustainability efforts. By delving into the intricate dynamics of wear phenomena within wheel–rail material, this research paves the way for innovative solutions that not only enhance operational efficiency but also minimise the ecological footprint of railway transportation. [ABSTRACT FROM AUTHOR]

This paper presents an investigation on the forming characteristics of the tailor rolled blank of an aluminum alloy (Al-TRB) during three-point bending at room temperature through experiments and finite element simulations. The strain distribution, spring-back characteristics, and metal flow law of 6000 series Al-TRB during three-point bending are explored. The prepared Al-TRB has good bending properties, and no surface cracks appear in the bending region of the Al-TRB when bent to 180°. Surface roughening occurs on the outside of the bending region. Since the strain in the thick zone is greater than that in the thin zone, the surface roughening in the thick zone is more obvious than that in the thin zone. The spring-back angle in the thin zone is higher than that in the thick zone after three-point bending, and the overall spring-back angle of Al-TRB becomes larger with an increasing bending angle. When the transition zone of Al-TRB is centered and the length of the transition zone is certain, as the length of the equal-thickness zone increases, the spring-back angle of the thin zone is larger, while the spring-back angle of the thick zone is smaller. Under the premise of a certain total length of Al-TRB and the length of the transition zone, the larger the length proportion of the thin zone, the larger the overall spring-back angle of Al-TRB, and the larger the length proportion of the thick zone, the smaller the overall spring-back angle of Al-TRB. In addition, a slight metal flow phenomenon exists during three-point bending, which shows that the metal in the bending region will flow to the thick zone, and the metal at the edge will flow to the thin zone. At the same time, there are localized thickening and thinning phenomena in Al-TRB. This study is helpful because it provides theoretical guidance for designing molds for the actual production of Al-TRB parts for automotives. [ABSTRACT FROM AUTHOR]

High‐speed trains (HSTs) often face challenges associated with car‐body hunting, resulting from factors such as complex operating environments and wheel‐rail contact degradation. These issues have a significant impact on the ride quality and operational safety. Passive suspension systems are inadequate to provide satisfactory dynamic performance for HSTs in such circumstances. However, active suspension systems can provide an effective solution. To address the car‐body hunting stability of HSTs, this study proposes a novel control approach called displacement inequality constraint following control (ICFC‐BIS) for the active suspension of HSTs. The ICFC‐BIS leverages the beneficial nonlinearity of bio‐inspired structures (BIS) to indirectly achieve excellent dynamic characteristics of the BIS through actuators installed in the suspension of HSTs, eliminating the need for actual BIS installation. Numerical simulation results demonstrate that the proposed ICFC‐BIS can effectively suppress car‐body hunting motion, thereby enhancing the ride comfort of HSTs. Consequently, the operational safety and ride comfort indices of HSTs equipped with active suspension systems are significantly improved. [ABSTRACT FROM AUTHOR]

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

The atomic‐level fundamental understanding of the rolling contact fatigue (RCF) mechanism using molecular dynamics (MD) simulation is yet to be understood more clearly. In this paper, the atomistic behavior of the single‐crystal Ni is studied under dynamic rolling contact loading with the help of MD simulations at varying temperatures of the specimen. The deformed material is investigated using atomic strain analyses to evaluate the shear, volumetric strain distribution, and von Mises stress. Furthermore, dislocation and stacking–fault analyses are done to determine the deformation mechanism of the material with the oscillation cycles. Simulation studies infer that dislocation defects tend to increase with the temperature of the specimen logarithmically. The deformation majorly results in partial dislocations, indicating low stacking fault (SF) energy. The present work opens up a new field of study to understand the RCF mechanisms, which can provide the foundational work to understand other face‐centered cubic (FCC) materials. Highlights: The degree of straining and defect generation depends on cycles and ambient temperature.Specimen undergoes relaxation as von Mises stress decrease with increasing cycles.Partial dislocations are more dominant, indicating low stacking fault energy. [ABSTRACT FROM AUTHOR]

Characteristics related to power transmission in the micro-domain, based on dry rolling contact of the gears, were investigated using a 3D-printed gear train with a pitch circle diameter of 84 µm in order to experimentally compare the power transmission efficiency in the macro- and micro-domains. For a basic gear train with two intermeshing gears, it was shown that the gear train in the micro-domain was capable of transmitting power to the same extent as in the macro-domain. However, in gear trains with complex power transmission paths, assuming a planetary gear train with multiple meshing gears, it has been shown that the power transmission characteristics of micro-domain gears differ from those in the macro-domain. The use of gear trains in the micro-region necessitates consideration of the loss of transmitted torque due to contact between tooth surfaces, which is unique to the micro-region and different from its use in the macro-region. [ABSTRACT FROM AUTHOR]

When high-speed trains operate under braking conditions, the wheel-rail interaction increases significantly, which can lead to more serious wear problems. To analyze the evolution of wheel wear and the dynamic characteristics of wheel-rail under braking conditions, this paper first carries out long-term monitoring of the service state of wheel-rail during the operation period. The study analyzed the matching characteristics of the measured wheel-rail profile and calibrated the wear model by using the collected data. The resulting wear prediction model was then used to examine the wheel wear characteristics under braking conditions. The research results indicate that during the operation period, the wheel experiences tread concave wear within a range of ±20 mm of the rolling circle, at a rate of approximately 0.05 mm per 10,000 km. Meanwhile, the rail experiences top surface wear at a natural rate of about 0.09 mm per year. Concave wear causes the contact point of the wheel-rail to appear in two zones, resulting in a sudden change of contact geometric parameters. The concave worn wheel and rail with a 60 N profile have better matching compared to the 60 rail profile. Increasing the braking torque and wheel-rail friction coefficient will significantly increase the wheel wear depth on straight sections. On small-radius curve sections, rail side lubrication can significantly reduce high rail side wheel flange wear. A worn concave wheel can lead to unfavorable wheel-rail contact geometry characteristics and increase low-frequency components in the vehicle's lateral dynamic response. [ABSTRACT FROM AUTHOR]

Focusing on the problem of strip shape quality control in the finishing process of hot rolling, a shape model based on metal flow and stress release with the application of varying contact rolling parameters is introduced. Combined with digital twin technology, the digital twin framework of the shape model is proposed, which realizes the deep integration between physical time–space and virtual time–space. With the utilization of the historical data, the parameters are optimized iteratively to complete the digital twin of the shape model. According to the schedule, the raw material information is taken as the input to obtain the simulation of the strip shape, which shows a variety of export shape conditions. The prediction absolute error of the crown and flatness are less than 5 μm and 5 I-unit, respectively. The results prove that the proposed shape simulation model with strong prediction performance can be effectively applied to hot rolling production. In addition, the proposed model provides operators with a reference for the parameter settings for actual production and promotes the intelligent application of a shape control strategy. [ABSTRACT FROM AUTHOR]

The heat transfer of a slab is significantly influenced by roll contact during the continuous casting process. The influence of roll contact calculation methods on the predicted heat transfer results has not been previously investigated. In this work, the non-uniform solidification of the wide-thick slab was studied with a 2D heat transfer model using real roll contact method (R. method) and equivalent roll contact method (E. method). The predicted slab surface temperature and shell thickness were verified with the measured results of the infrared camera and nail shooting experiments, respectively. Then, the predicted heat transfer results (including the slab surface temperature, mushy region length, and solidification end position) for the wide-thick slab with different thicknesses and different casting speeds were calculated using the E. method and R. method, and the influence of these two roll contact methods on the predicted heat transfer results was discussed for the first time. The results show that both these two roll contact methods could be applied to accurately predict the slab surface temperature without considering the transient temperature dips in the roll–slab contact regions. However, the deviation of the predicted mushy region length and solidification end position using the E. method are obvious. Compared with the R. method, the predicted mushy region length obtained using the E. method is larger and the solidification end obviously subsequently moves along the casting direction. [ABSTRACT FROM AUTHOR]

The application feedback on existing silicon nitride ceramic bearings and RCF experimental research all indicate that the primary failure mode of silicon nitride ceramic bearings is material spalling on the contact surface. Spalling failure occurs due to the initiation and propagation of cracks under rolling contact. However, silicon nitride ceramic bearings, owing to their unique manufacturing method, inevitably exhibit defects and cracks. Therefore, as silicon nitride ceramic bearings are increasingly prevalent, reducing the probability of spalling failure is crucial for extending their service life. This can only be achieved by gaining a clear understanding of the crack initiation and expansion mechanisms in silicon nitride ceramic bearings. This paper is based on silicon nitride rolling friction experiments. It involves the joint simulation of Franc3D-V8.4 and ABAQUS2020, wherein the crack front SIFs are calculated for each load contact position of the surface crack on the silicon nitride ceramic bearing ring during cyclic movement. The study also delves into the determination of the maximum effective stress intensity factors and explores the influence of the initial crack depth on the cycle life and direction of crack propagation. The research yields several valuable conclusions. The findings of this research offer theoretical guidance for formulating grinding technologies for silicon nitride rings and adjusting and controlling working parameters of silicon nitride ceramic ball bearings. These insights are crucial for enhancing the reliability and longevity of silicon nitride ceramic bearings in practical applications. [ABSTRACT FROM AUTHOR]

This paper is concerned with the modeling of power dissipation due to friction and its relation with wear estimation in wheel–rail contact. Wear is a complex multi-scale and multi-physical phenomenon appearing in rolling contact. Wear is generated by high contact stress and the work of friction forces. This phenomenon leads to the appearing of the worn material in the form of wear debris between contacting surfaces. In contact models, wear is usually described in terms of the wear depth function. This function modifies the gap between the contacting bodies as well as the shape of the surfaces of the wheel and rail in contact. In this paper, besides the wear depth function, the dissipated energy, rather than the contact stress, is taken into account to evaluate the wear impact on rail or wheel surfaces. The dissipated energy allows us to more precisely evaluate the wear debris amount as well as the depth of wear and its distribution along the contact interface. A two-dimensional rolling contact problem with frictional heat flow is considered. The elasto-plastic deformation of the rail is considered. This contact problem is governed by a coupled system of mechanical and thermal equations in terms of generalized stresses, displacement and temperature. The finite element method is used to discretize this problem. A discretized system of equations with nonpenetration and friction conditions is transformed and formulated as a nonlinear complementarity problem. The generalized Newton method is applied to numerically solve this mechanical subproblem. The Cholesky method is used to find the solution of the heat-conductive problem. The dissipated power is evaluated based on the resultant force and slip at a reference point. Numerical results including the distribution of slip velocity, power factor and wear rate are provided and discussed. [ABSTRACT FROM AUTHOR]

Rail transportation is a pivotal mode of land transport for its efficiency in transporting passengers and freight across short or long distances; hence, the reliability and safety of rail systems are of key importance. Rolling contact fatigue (RCF), characterized by the cyclic loading of wheel-rail contacts, presents a significant challenge in the rail industry. This study presents a comprehensive numerical investigation on the influence of different crack orientations on the contact stress of the rail profile and subsequently the fatigue life. Using finite element analysis (FEA) with Abaqus and FE-safe software, the study examined different crack orientations' impact on stress distribution and fatigue life of rail profiles. Employing the extended finite element method (XFEM), this study modeled cracks in rail profiles with different orientations: parallel, perpendicular, and oblique to the rail axis. finite element analysis was used to obtain stress distribution results, highlighting the impact of crack presence, and orientation on maximum contact stresses. Subsequently, fatigue analysis was performed using FE-safe software, wherein the FEA results were imported to estimate fatigue life and damage evolution. The study revealed that the presence of a crack significantly influences contact stress, fatigue life, and damage accumulation. The results further demonstrated that crack orientation has an impact on the severity of those effects. Oblique cracks exhibited higher impact compared to lateral and longitudinal cracks. The study provides valuable insights into rolling contact fatigue-related failures, aiding in better understanding and mitigation of such issues, thereby contributing to improved rail maintenance practices and system safety. [ABSTRACT FROM AUTHOR]

The development of thermomechanical coupled simulations for rolling contacts is challenging when the adjacent material is temperature-dependent or when there are cracks or other discontinuities on the contact surface. This paper proposes a novel thermomechanical coupled modeling method for rolling contacts using a nonlocal peridynamic (PD) approach. Fully coupled, ordinary state-based PD thermomechanical equations for the plane strain and plane stress cases are derived based on the strain-energy density, including thermal coupling terms, and detailed information on each parameter is provided. Subsequently, an algorithm for rolling thermal contacts in PD is proposed based on the penalty method. This study further provides a detailed modeling process and an algorithm for the proposed method based on a multi-rate time-integration scheme for numerical implementation. A typical two-dimensional (2D) wheel–rail rolling contact model is established to evaluate the performance of the proposed contact modeling method in wheel–rail thermal contact and to analyze the influence of temperature-dependent material and rail-surface cracks on the thermomechanical response. It is found that the contact stress and rail-surface temperature rise in the case of small creepages and temperature-independent materials are in good agreement with the analytical solution. In the case of large creepages, the mechanical and temperature results of using temperature-dependent materials and temperature-independent materials are quite different, and the frictional heat generated can cause martensitic transformation of adjacent materials. Rail-surface cracks cause a sharp increase in the contact stress and temperature rise near the cracks, and the high temperature also promotes crack growth. • A nonlocal thermomechanical coupled modeling method for rolling contacts using peridynamic is proposed. • Fully coupled, ordinary state-based PD thermomechanical equations are derived. • An algorithm for rolling thermal contacts in PD is proposed based on the penalty method. • A typical 2D wheel–rail rolling contact model is established for a case study. [ABSTRACT FROM AUTHOR]

Oil–air lubrication has proven to be very effective for high-speed bearings because the oil supply in the form of droplets can be precisely controlled. This work uses optical interferometry to study the mechanism of lubricating film formation in rolling point contact with oil droplet lubrication. The effect of a double oil drop pair, where two oil droplets are positioned in mirror images about the central axis of the lubricated track, is examined. The process by which pairs of oil droplets approach and lubricate a bearing contact is analysed. This study also covers the effect of multiple oil droplets supplied in a tailored or a random dispersion pattern. Additionally, the effects of oil viscosity, entrainment velocity, and droplet distribution on starvation are also investigated. [ABSTRACT FROM AUTHOR]

This paper examines the difference between the effects of anti-wear additives on vegetable and hydrocarbon-based oils. Knowledge of the specific influence of additives on the anti-wear properties of vegetable oils is necessary to increase the efficiency of the development of biodegradable lubricating oils. In addition, this is interesting from the point of view of clarifying the mechanism of action of AW/EP additives. The effect of non-toxic additives—adipic acid monoester and hexadecanol—on hydrocarbon hydrocracking oil and vegetable oil was compared. The comparison was carried out in rolling contact with sliding, sensitive to the separating ability of the oil. It was found that in hydrocarbon oil, the additive affects the parameters of the hydrodynamic friction regime. When adding an additive to vegetable oil, the hydrodynamic parameters do not change. The additive acts in the same way in both oils during mixed and transient modes. The obtained results are compared to available data, and an explanation of the difference is proposed based on the AW/EP mechanism of action. It is concluded that there is little chance of enhancing vegetable oil properties for hydrodynamic bearings. Search criteria for additives that effectively influence the antifriction and anti-wear properties of vegetable oils in mixed and boundary friction modes are proposed. [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]

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.)

An improved moment of load path model for rolling contact fatigue life prediction is proposed in this paper. First, the complex multiaxial stress variation of the subsurface materials under rolling contact conditions was analyzed by the finite element method. Next, the equivalent stress parameter was presented to characterize the complex stress state based on the improved moment of load path method. The key concept of the proposed method is building a new coordinate system for analyzing the load path of the complex multiaxial stress state. The efficiency of the proposed model was validated with different kinds of fatigue test results in the existing literature. The model results show a good agreement with the test data. Finally, the model was used to obtain the relationship of the Hertz stress versus fatigue life under rolling contact conditions according to the fatigue life data. Highlights: The proposed multiaxial life prediction model considers the hydrostatic stress.The correlation of the multiaxial test data is built using a defined stress parameter.Rolling contact fatigue life is predicted by the proposed multiaxial model. [ABSTRACT FROM AUTHOR]

Sliding and spinning behaviors significantly affect the performance of rolling bearings, especially for dry-lubricated bearings, micro and macro sliding may lead to increased wear of the solid lubricating film. A unified rolling contact tribology analytical model is proposed for dry-lubricated angular contact ball bearings (ACBBs) considering the extreme conditions including high combined loads and rolling contact effects. A comprehensive solution framework is proposed to ensure the robustness of the model under different loading conditions. Equilibrium equations are solved to study the effects of friction coefficients, rotating speeds, and combined loads on the skidding and spinning characteristics of the ACBB. The results show that the rolling contact effects and combined loads significantly affect the skidding and spinning performance of the ACBB. Further analysis reveals that the skidding mechanism is related to the interaction between ball kinematical motion and traction forces. The developed analytical model is proved to more accurately predict the bearing kinematical and tribological behavior as it discards the raceway control hypothesis and considers the macro/micro-slipping, creepage, and self-spinning motions of the ball, which is validated using both the existing pure axial loading dry-lubricated ACBB model and the classical Jones—Harris model. The study would provide some guidance for the structure and lubrication design of dry-lubricated ACBBs. [ABSTRACT FROM AUTHOR]

Copyright of Railway Standard Design is the property of Railway Standard Design 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.)

The effects of cyclic loading on the surface microstructure evolution of different contact locations in a used pearlitic rail were studied. Microstructures were analyzed using Scanning Electron Microscopy (SEM). Meanwhile, grain boundaries and crystallographic orientations were explored via Electron Backscatter Diffraction (EBSD). At last, wheel–rail contact probabilities and forces were calculated using rail profiles. The results indicate that the side wear region located in the gauge face was 71.5% in the high-angle grain boundaries (HAGBs) fraction, 0.88 in the Kernel Average Misorientation (KAM) value, 36% in the recrystallization (REX) fraction, and had a predominant orientation in grains. The rolling contact fatigue (RCF) region situated at the gauge corner was 66.3% in the HAGBs fraction, 0.92 in the KAM value, 33% in the REX fraction, and was mis-orientated in grains. The region located at the edge of the running band was 60.7% in the low-angle grain boundaries (LAGBs) fraction, 0.97 in the KAM value, 12% in the REX fraction, and was mis-orientated in grains. Continuous dynamic recrystallization (cDRX) took place in wear and RCF regions during the cyclic rolling contact loading, creating ultra-fine grains with a transformation from LAGBs to HAGBs, lower KAM values, and more REX. Grains oriented along [111] parallel to the vertical direction in the wear region were influenced by the dominant normal force, while grains in the RCF region were non-oriented, which was attributed to large lateral and vertical forces of similar magnitudes. [ABSTRACT FROM AUTHOR]

The ongoing digitalization of processes and products in mechanical engineering is accompanied by an increasing demand for data. In order to provide this data, technical systems are being extended with sensory functions. To supply those sensory functions on rotating elements—such as shafts—with electrical energy, and to be able to transmit signals out of the system, sliding contacts can be used as a cost-effective and established solution. However, if electrical properties of machine elements are utilized for sensing purposes, such as condition monitoring of rolling element bearings by means of impedance measurement, sliding contacts are directly in the measurement path and can thus influence the measured impedance. The aim of this paper is to analyze the impedance of graphite and silver graphite carbon brushes under different rotational speeds, in different positions, and with different carrier frequencies. The material of the carbon brushes as well as the position have significant effects on the impedance behavior. Furthermore, carbon brushes show a significant running-in behavior. The results are discussed, and indications for use in impedance measurements are given. Silver graphite carbon brushes in axial positioning are particularly suitable for impedance measurements of sensory utilizable machine elements. Sufficient running-in time must be considered. [ABSTRACT FROM AUTHOR]

This article investigates the phenomenon of bifurcation induced by double grazing in a piecewise-smooth oscillator with a play, which is a common occurrence in many non-smooth dynamical systems namely gear systems with approval, flange contact in wheel-rail systems, and spacecraft docking. The study is carried out using a composite Poincaré mapping with bilateral constraint, which extends the local normal form mapping of one discontinuity boundary to two discontinuity boundaries. The paper first derives the local discontinuous mapping at the unilateral grazing point using the normal form of discontinuity mapping and determines the type of 3/2 singularity of the zero-time discontinuous mapping with a continuous vector field at the discontinuity boundary. The composite Poincaré mapping is then used to obtain non-classical local bifurcations caused by double grazing, including bifurcation from period-1 motion to period-2 motion, bifurcation from period-1 motion to period-3 motion, and bifurcation from period-1 motion to chaos. The results of the study are consistent with those obtained via direct numerical simulations, demonstrating the efficacy of the composite Poincaré mapping of double grazing. The paper sheds light on the behavior of non-smooth dynamical systems and provides insights into the mechanisms underlying bifurcation induced by double grazing. The findings have potential applications in various fields including engineering, physics, and biology. [ABSTRACT FROM AUTHOR]

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

The detection of bearing defects while the machinery is in use is essential for predicting the incipient failure and thereby providing an opportunity to take remedial measures for preventing the costly downtime and ensuring the safe and efficient operation of rotating machinery. With the increasing availability of vibration sensor data and the development of machine learning techniques, the ML methods have become a popular approach for automated fault diagnosis in bearings. In this paper, an attempt has been made to detect the faults in the outer race of bearing using different ML algorithms. An experimental setup has been designed and fabricated to conduct experiments on healthy and faulty bearings and the vibration signals were captured. The captured vibration signals were directly employed as images for training the ML algorithms without the need for conducting the spectral analysis. Six machine learning algorithms, namely, Linear Regression (LR), Decision Tree (DTR), KNN Regression (KNNR), Random Forest Regression (RFR), Convolution Neural Network (CNN), Naive Bayes (NB) were separately applied to classify the location of defects within the outer race of the ball bearing. The accuracy table are used to find the best suitable algorithm for the predictions. The methodology includes data preprocessing techniques, network architectures, training strategies, and evaluation metrics. It has been established that the use of ML technique is very effective in detecting the bearing defects and CNN is able to achieve 100% accuracy. [ABSTRACT FROM AUTHOR]

The Lundberg-Palmgren (L-P) fatigue life formula, as a statistical fatigue theory, has been widely used in the industry. However, its direct applicability is limited to the components treated by surface strengthening technologies. Rolling contact fatigue tests and surface integrity measurements of American Iron and Steel Institute (AISI) 9310 rollers with several surface treatments were performed to address this issue. Based on these results, a modified L-P fatigue model was proposed, enabling the consideration of surface modification including surface roughness, residual stress, and hardening introduced by different surface treatments. Compared with the original L-P fatigue formula, its results are more accurate for surface strengthened specimens. Furthermore, this method can assess the contact fatigue life of gears treated by surface strengthening techniques. [ABSTRACT FROM AUTHOR]

Using lightweight systems and friction reduction approaches are two main contributors towards modern and efficient powertrains in the automotive industry. New materials and processes are required to achieve the demanding and ever-increasing performance requirement of automotive systems. Nanostructure induced by severe plastic deformation methods involves bimodal microstructures and hence, shows exceptional mechanical characteristics which can be exploited for automotive application. Through this study, samples were prepared using pure copper, aluminum alloy (series 7000) and were processed to attain bulk nanostructured samples using a Single Step High Pressure Torsion technique with appropriate dimensions applicable as the rolling elements of automotive bearings. The induced nanostructures resulted micro hardness and frictional characteristics of the bulk samples were assessed using transmission electron (TEM) and atomic force (AFM) microscopies as well as microhardness evaluations. The results revealed that a fully refined nanostructured samples were achieved with 90% increase in the hardness at the outer diameter of the sample. The AFM measurements indicated that the friction coefficient of nanostructured copper and aluminum samples were ~ 25 and ~ 45% less than that of both the unprocessed samples, respectively. Characteristics of treated samples suggest that these processes can be potentially used in demanding conditions of rolling element bearings with reduced weight and frictional losses. [ABSTRACT FROM AUTHOR]

At the entry of the pickling and tandem cold strip mill (PL-TCM), the unreasonable cut length of the head and tail of the strip often causes a thickness difference between the weld surfaces of the front and back strip, resulting in a weld seam with thickness difference after welding. This can easily lead to strip breaking at the weld seam in the cold rolling process. In this paper, a finite element model of roll and strip with weld seam is established to investigate the mechanism of strip breaking at weld seam due to thickness difference. By simulating the working conditions in the rolling process for weld seam with different thickness differences, the evolution of the stress state of the weld seam in the rolling process under each working condition is analyzed. The influence of thickness difference in the rolling process of the weld seam is revealed, and the effect of thickness difference on the risk of strip breaking at weld seam during the rolling process is further discussed. According to the research results, the optimization method of strip head and tail shear length was designed and applied to the industrial site. After application, the accident rate of strip breaking is reduced and the effect is as expected. [ABSTRACT FROM AUTHOR]

The effect of variable DC bearing current amplitude, bearing current polarity, mechanical force, rotation speed, bearing temperature, and number of the balls on the fluting in an axial ball bearing type 51208 is investigated under DC currents. The results are obtained from two different test setups with two different lubricants (mineral-oil-based grease and polyglycol oil). The speed varies between 100 rpm and 2000 rpm, the axial bearing force between 200 N and 2400 N, the DC current amplitude between 0.5 A and 20 A, the bearing temperature between 29 °C and 80 °C, the number of steel balls per bearing between 3 and 15, and the test duration between 6 h and 168 h. The results show that with a higher bearing current density and/or a higher bearing speed, a lower bearing force and/or a lower bearing temperature, a bigger number of roller elements, but also at a negative polarity of a DC electric bearing current, the occurring of fluting is more probable and occurs at an earlier stage of operation. [ABSTRACT FROM AUTHOR]

This work presents an investigation on the influence of pitting in EHL rolling contact. The pitting geometry comes as an extension on the architecture for multi-physical numerical calculations of rolling element bearing contacts based on OpenFOAM. The model utilized is built according to the state-of-the-art for fluid–solid interaction and electro-quasi-static fields. In this framework, the contact is reduced to be two dimensional in order to reduce the computing costs needed. The changes in the electric properties, which are caused by pittings, are measured using the electric capacitance of the contact and put in perspective with regard to the EHL contacts geometry. The investigation delivers an evaluation on how surface degradation, in both the pitting width w and pitting depth d of the contact, affects the electric properties. It can be seen that the maximum deviations with different reduced radii for the same pitting structures are around 5% and would therefore hardly be distinguishable with corresponding measurements. By comparing the same data for the same ratio of pitting width to reduced radius, on the other hand, differences of up to 50% can be seen. [ABSTRACT FROM AUTHOR]

In railway systems, layered structures could be induced in wheel–rail contact interfaces due to several causes, such as head hardening, work hardening, plastic deformation, and mechanical or thermal excursion-induced phase transformation. This study proposes an explicit finite element (FE) method for investigating elastic layer effects in wheel–rail rolling contact. The proposed method is first validated by comparing its solution with that of Kalker's boundary element method (BEM) when the layer is not present, with a focus on the tractive rolling contact. To investigate general layer effects, the rail is assumed to consist of two layers, i.e., the top layer and the matrix material. The top layer is assumed to have different elastic moduli from the matrix material and then the top elastic layer effects on contact characteristics such as contact stress, contact patch, and subsurface stress are investigated. Different layer thicknesses are also considered. It is observed that a harder layer tends to introduce larger contact pressure and surface shear stress, but a smaller contact patch. A harder layer also produces larger subsurface stresses. A thicker layer may intensify these effects. The results suggest that in engineering applications, the analysis of wheel–rail rolling contact consequences such as wear and rolling contact fatigue (RCF) may need to consider the layered structures using appropriate methods. [ABSTRACT FROM AUTHOR]

Copper impregnated carbon/carbon composite (Cu-C/C composite) was fabricated for novel sliding collector material by weaving carbon fiber, heat treatment and Cu alloy impregnation. The effects of counterpart materials (Fe ball and Cu ball) on friction and wear behaviors were investigated and compared with the result of carbon contact strip used in high-speed railway. Morphology, chemical composition, phase and structure of wear surface and tribolayer were characterized to clarify tribological mechanisms. The results show that friction coefficient follows the order: Cu-C/C composite/Cu ball > carbon contact strip/Fe ball > Cu-C/C composite/Fe ball > carbon contact strip/Cu ball. The carbon crystalline of wear surface appears preferred orientation along the sliding orientation, which is benefit for boundary lubrication. When the counterpart material is Fe ball, Cu-C/C composite is superior to pure carbon strip in mechanical strength, electrical conductivity, wear resistance and friction performance. [ABSTRACT FROM AUTHOR]

In the present study, the concept of utilizing two circular cam-track disks, of the same central angle, in combination with one circular roller is presented. The roller is restrained to move within a vertical groove, and at the same time it rotates with rolling-contact on both cam tracks. When the upper cam is fully travelled by the roller, the same occurs with the lower one, despite their different lengths. Therefore, during the rolling contact, the two cams always sweep the same central angle. The aforementioned configuration of the two circular arcs may be considered as a unit cell, which can be repeated an even number of times, and when folded forms a closed circular groove between two cam-track disks. For better understanding, a manufactured prototype and 3D CAD-models have been developed. The operation of this setup as a gearless automotive differential is demonstrated by performing two bench experiments, which are then explained by a simplified mechanical model. The latter focuses on the implementation of the principle of the inclined plane, in which an upper limit of the inclination angle is imposed in accordance with the coefficient of friction at the friction disks. Previous patents on gearless differentials are discussed and other possible applications in mechanical engineering are outlined. [ABSTRACT FROM AUTHOR]

Surface initiated rolling contact fatigue (RCF) of gears and rolling bearings can lead to premature failure in mechanical transmission systems. The orientation of surface crack initiation closely depends on surface tractive force, while the mechanism leading to this dependence is still obscure. In this work, a numerical model is proposed to investigate the effect of friction on surface crack initiation in RCF. An inhomogeneous contact solver based on semi‐analytical method (SAM) is developed by combining the damaged‐coupled constitutive relation and the Eshelby's equivalent inclusion method. The damage accumulation and concurrent degradation of material properties are modeled with continuum damage mechanics (CDM). The effect of surface tractive force on the orientation of surface crack initiation is simulated and analyzed. Results indicate that the progressive evolution of damage under the cyclic loading is accompanied by the stress variation around the damaged area. The damaged area increases, and the crack initiation life decreases with an increasing coefficient of friction. Highlights: A new damage evolution model incorporating an inhomogeneous contact solver is developed.The possible causes of the orientation of surface crack affected by friction traction are analyzed.The simulated results of damage evolution and stress variation agree well with open literatures. [ABSTRACT FROM AUTHOR]

The prediction of wheel/rail rolling contact fatigue (RCF) crack initiation during railway operations is an important task. Since RCF crack evolution is influenced by many factors, its prediction process is complex. This paper reviews the existing approaches to predict RCF crack initiation. The crack initiation region is predicted by the shakedown map. By combining the shakedown map with various initiation criteria and the critical plane method, the crack initiation life is calculated. The classification, methodologies, theories and applications of these approaches are included in this paper. The advantages and limitations of these methods are analyzed to provide recommendation for RCF crack initiation prediction. This review highlights that wheel/rail dynamic characteristic, complex working conditions, surface defects and wear all affect the RCF crack initiation. The optimal selection of criteria is essential in the crack initiation prediction. Based on the research gap regarding the challenging process of crack initiation prediction detailed in this review, a proposed prediction process of RCF crack initiation is proposed to achieve a more accurate result. [ABSTRACT FROM AUTHOR]

The wear performance of AlSi7Mg0.6 aluminum alloy, a casting aluminum alloy used in positioning devices for catenary systems of high-speed railways which fail frequently on lines where the speed of trains is higher than 300 m/s, is discussed in this study. It was estimated that sliding contact wear occurred and mainly contributed to the failure. To explore the competing mechanism for frictional wear failure, frictional experiments based on three groups of sliding distance (0.5 mm, 1.5 mm and 3.0 mm) and four groups of applied loads (20 N, 50 N, 100 N and 200 N) were implemented. Three-dimensional morphological observation results revealed that the wear volumes at a sliding distance of 0.5 mm were only about 1/10 of that at a sliding distance of 3.0 mm. It was also revealed that the wear volume based on a sliding distance of 3.0 mm and applied load of 20 N was still much larger than the wear volume under a sliding distance of 0.5 mm and applied load of 200 N. SEM observation of the microstructures revealed that abrasive wear was the dominant wear mechanism in dry sliding friction conditions. A simplified positioning device model was also established to study the influence of tension force on wear performance. The simulation results revealed that smaller tension force between the positioning support and positioning hook would lead to higher relative sliding distance and larger wear depth. Sliding contact friction should be avoided due to relatively large wear efficiency compared with rolling contact friction. Both experimental and simulation results suggested that proper tension force was preferred in assembling components which could ensure rolling contact friction rather than sliding contact friction. [ABSTRACT FROM AUTHOR]

In the presented work, a parametric multibody simulation model is presented that is capable of predicting the friction torque and kinematics of tapered roller bearings. For a highly accurate prediction of bearing friction, consideration of solid and lubricant friction is mandatory. For tapered roller bearings in particular, the friction in the contact between the rolling element and raceway is of importance. Friction forces in the contact between the rolling element end face and inner ring rib as well as roller cage pocket contacts are also considered in the model. A large number of tests were carried out to validate the model in terms of the simulated frictional torque. Influencing variables such as speed, axial load, radial load, and temperature were investigated. The simulation results show good agreement with the measured friction torque, which confirms that the model is well suited to predict frictional torques and therefore the kinematics of tapered roller bearings. [ABSTRACT FROM AUTHOR]

Railway systems play a pivotal role in modern transportation networks, contributing to both efficiency and environmental sustainability. This study investigated the multifaceted aspects of wear phenomena in railway engineering, focusing on their significant implications for environmental costs and operational efficiency. Experimental trials were conducted using a high-performance bi-disc apparatus, evaluating a range of materials, contact pressures, and lubrication conditions. Shakedown maps were employed to assess ratcheting behaviour, while the wear rate was analysed as a function of the fatigue index (FI). The results reveal the intricate interplay of contact pressure, slip ratio, material properties, and lubrication in determining wear and ratcheting behaviour. Oxidative and mild wear mechanisms were identified, and wear debris composition and morphology were characterised. The outcomes from this research clarify the pivotal role that wear processes play within railway systems and the far-reaching environmental repercussions they entail. This exploration contributes to the ongoing optimisation of railway operations, offering valuable insights aimed at mitigating unavoidable pollution sources and strengthening sustainability efforts. By delving into the intricate dynamics of wear phenomena within wheel–rail material, this research paves the way for innovative solutions that not only enhance operational efficiency but also minimise the ecological footprint of railway transportation.

The work rolls of CVC rolling mill usually adopt S-shaped roll profile curve in the rolling process of plate, which changes the contact between the rolls and causes the contact pressure distribution between the rolls to be uneven. The peak of the contact pressure between the rolls appears at the end of the roll, which leads to peeling or "meat loss" at the end of the roll and poor plate crown control effect. To solve those problems, a CVC rolling mill backup roll profile curve with parabolic chamfer was proposed, and the fusion model of plate crown based on mechanism and data-driven models was developed. Combining the parameters of the CVC roll profile curve, the theoretical calculation formula of the backup roll chamfering was deduced. According to the actual data of the plate rolling mill, the parameters of different types of backup roll chamfering were determined, and the distribution of contact pressure between the rolls under different backup roll chamfering was calculated and analyzed by finite element model. Based on the new parabolic chamfer curve of backup roll, the rolling force setting model based on Extreme Learning Machine (ELM) and roll wear model based on Genetic Algorithm Artificial Neural Network (GA-ANN) were constructed by using the nonlinear fitting ability of machine learning algorithm. Then, the predicted results of rolling force and roll wear were taken as the input variables of plate crown prediction. At the same time, the roll system deformation model and roll bending force model based on mechanism model were introduced as inputs to construct the plate crown Convolutional Neural Network (CNN) model based on mechanism and data-driven fusion. The simulation results show that the parabolic chamfer can significantly reduce the pressure between the backup rolls. When the rolled strip width is 2000 mm, 2400 mm, and 2800 mm, the parabolic chamfer can reduce the peak contact stress between the rolls by 8.6% and 10.8%. When the rolling bending force is 1600kN, 2100kN, and 2600kN, the parabolic chamfer can reduce the peak contact stress between the rolls by 8.6%, 8.9%, and 9.1%. The hit ratio of plate crown increased from 90.4% to 96.5%, and the product degradation rate caused by the shape problem decreased by 35.5%. [ABSTRACT FROM AUTHOR]

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To reveal the influence of surface morphology characteristics in mixed lubrication on the contact characteristics of the rolling interface, a random three-dimensional rough surface model based on Gaussian distribution theory was established. The model utilizes the finite element method (FEM) to simulate the regular contact and tangential sliding behavior of micro-asperities at the rolling interface in mixed lubrication conditions. The connection bearing capacity of models with varied roughness in mixed lubrication was studied. Furthermore, the effect of various sliding and normal indentation amounts on the normal and friction stress was investigated. The simulation result reveals that the roughness of the surface influences the distribution of the lubricating oil film. The lubricating oil layer between the interfaces with a lower roughness has a higher bearing capacity due to its more uniform distribution of peaks and valleys. An increase in the normal indentation amount raises the friction stress and normal stress. In contrast, an increase in sliding lowers the normal pressure, substantially impacting the fluctuation of the friction coefficient dramatically. Finally, the random three-dimensional rough surface model is verified by comparing it with the experimental data in the related literature. [ABSTRACT FROM AUTHOR]

Friction force is a crucial factor causing power loss and fatigue spalling of rolling element bearings. A combined experimental and analytical method is proposed to quantitatively determine the elastohydrodynamic lubrication (EHL) friction force distribution between rollers and outer raceway in a cylindrical roller bearing (CRB). An experimental system with the instrumented bearing and housing was developed for measuring radial load distribution and friction torque of bearings. A simplified model of friction force expressed by dimensionless speed, load, and material parameters was given. An inequality constrained optimization problem was established and solved by using an experimental data-driven learning algorithm for determining the uncertain parameters in the model. The effect of speed, load, and lubricant property on friction force and friction coefficient was discussed. [ABSTRACT FROM AUTHOR]