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Purpose: The paper aims to find the correlation between the microparameters and the macroparameters of the soil. The study aims to calibrate the macroscale and microscale parameters of rolling resistance contact models to successfully apply the discrete element method to do some research of the geotechnical problem. Design/methodology/approach: The paper opted for an exploratory study using the PFC3D to simulate the triaxial tests that include more than 50 cases and the coupling analysis method, which considering several effect of various factors. Findings: The paper provides a quantitative relationship between the macroparameters and microparameters of the rolling resistance linear model and a method for fast calibration of macroscopic parameters is proposed and verified by a triaxial test example. Originality/value: This paper provides the quantitative relationship of micro and macroparameters in the rolling resistance linear model by studying a single factor and considering the coupling effect of various factors and a fast method for the calibration of microparameters based on the rolling resistance linear model is proposed. [ABSTRACT FROM AUTHOR]

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]

Wheel–rail surface damage in curves can be effectively reduced with a lower vehicle Primary Yaw Stiffness (PYS), while lowering PYS is detrimental to ride comfort and vehicle stability. This trade-off can be addressed by integrating hydraulic damping into primary suspension. However, work in this area only concentrated on comparing the effects of specific devices – the full potential of the hydraulic-damping-integrated primary suspension on combating the trade-off considering the whole parameter space is still unknown. Here we address this by making the following two contributions: (1) fully exploring the potential of hydraulic-damping-integrated primary suspension, on minimising the PYS while maintaining ride comfort; (2) systematically investigating the trade-off between the PYS reduction and suspension stroke requirement. Based on a case study using the Mark 4 Coach, this paper found that the optimal hydraulic-damping-integrated suspension can reduce PYS by 97% over the default without worsening comfort. This large reduction can potentially lead to a significant lifetime wheel-rail maintenance cost saving of approximately £42M for the fleet. If a larger suspension stroke is allowed, more cost saving can be achieved. These results provide motivation to conduct detailed engineering design studies to further examine the trade-off between financial benefits and design complexity. [ABSTRACT FROM AUTHOR]

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

Purpose: The purpose of this paper is to examine the practicability of the self-designed ambient humidity controllable pin-disc/rolling multifunctional friction and wear test device and to evaluate the friction and wear characteristics of materials under diverse ambient humidity conditions in different contact forms. Design/methodology/approach: The practicability of the self-designed multifunctional friction tester was examined by the friction and wear tests of materials under different ambient humidity conditions [65%RH, 98%RH (relative humidity)] in diverse contact forms (pin/disc and rolling). Meanwhile, the friction and wear properties of pin/disc samples also rolling samples were assessed from three aspects: average friction coefficient, wear mass and wear morphology. Findings: The results prove that the self-designed multifunctional friction tester has practicability. Therefore, it can be used to simulate the friction and wear tests of materials under diverse ambient humidity conditions in different contact forms. Besides, it is evident that the wear damage of pin/disc and rolling samples are greatly improved under high ambient humidity conditions. And when other conditions are identical, the higher the ambient humidity, the smaller the average friction coefficient, wear mass and wear damage degree of pin/disc also rolling samples. Originality/value: This paper offers a self-designed multifunctional friction and wear test device. And the tester not only can realize the control of test ambient humidity, but also achieve the wear test of pin/disc or rolling contact forms. The design and production of the tester can offer convenience for the research of tribology, and provide fundamental guidance for the study of materials under high humidity condition in diverse contact forms. [ABSTRACT FROM AUTHOR]

A dual chemically reactive multilayer coating is rationally subjected to mono- and dual-functionalization through a 1,4-conjugate addition reaction at ambient conditions to depict the raising of the oil contact angle and rolling of a beaded oil-droplet underwater, respectively, only in the presence of targeted toxic chemicals (e.g. nitrite ion and hydrazine). Rational switching of the hydrophobic aromatic moiety into a hydrophilic moiety in the modified multilayer coatings via selected modified Griess reaction and Schiff base reaction contributed to the desired change in underwater oil-wettability and oil-adhesion. Eventually, this approach allowed equipment-free and naked-eye chemical sensing with high selectivity and sensitivity. [ABSTRACT FROM AUTHOR]

Wheel burn can affect the wheel–rail contact state and ride quality. With long-term operation, it can cause rail head spalling or transverse cracking, which will lead to rail breakage. By analyzing the relevant literature on wheel burn, this paper reviews the characteristics, mechanism of formation, crack extension, and NDT methods of wheel burn. The results are as follows: Thermal-induced, plastic-deformation-induced, and thermomechanical-induced mechanisms have been proposed by researchers; among them, the thermomechanical-induced wheel burn mechanism is more probable and convincing. Initially, the wheel burns appear as an elliptical or strip-shaped white etching layer with or without deformation on the running surface of the rails. In the latter stages of development, this may cause cracks, spalling, etc. Magnetic Flux Leakage Testing, Magnetic Barkhausen Noise Testing, Eddy Current Testing, Acoustic Emission Testing, and Infrared Thermography Testing can identify the white etching layer, and surface and near-surface cracks. Automatic Visual Testing can detect the white etching layer, surface cracks, spalling, and indentation, but cannot detect the depth of rail defects. Axle Box Acceleration Measurement can be used to detect severe wheel burn with deformation. [ABSTRACT FROM AUTHOR]

Rail wear occurs continuously owing to the rolling contact load of trains and is fundamental for railway operational safety. A point‐based manual rail wear inspection cannot satisfy the increasing demand for rapid, low‐cost, and continuous monitoring. This paper proposes a depth‐plus‐region fusion network for detecting rail wear on a running band, which is a collection of wheel–rail interaction traces. The following steps are involved in the proposed method. (i) A depth map estimated by a modified MiDaS model is utilized as guidance for exploiting the depth information of the running band for rail wear detection. (ii) The running band of a rail is segmented and extracted from images using an improved mask region‐based convolutional neural network that uses the scale and ratio information to perform instance segmentation of the running band images. (iii) A two‐channel attention–fusion network that classifies rail wear is constructed. In this study, we collected real‐world running band images and rail wear‐related data to validate our approach using a high‐accuracy rail‐profile measurement tool. The case‐study results demonstrated that the proposed method can rapidly and accurately detect rail wear under different ambient light conditions. Moreover, the recall rate of severe wear detection was 84.21%. [ABSTRACT FROM AUTHOR]

To reveal the characteristics of strip shape and roll change during the rolling process of six-high cold rolling mill (SHCRM), a three-dimensional finite element model of SHCRM was established by computer-aided design. The coupling deformation under various working conditions such as friction coefficient and bending roller force was analysed. Results show that the width of the plate, the amount of pressure, the friction coefficient, the rolling force, and the bending force are the key affecting factors of the deformation of the roller system, the shape of the load roll seam and the contact stress and strain. The deformation of the roll system, the shape change of the load roller seam and the stress and strain of the contact region are revealed. The obtained conclusions provide a reference for the development of rolling model of high cold rolling mill. [ABSTRACT FROM AUTHOR]

Angular contact ball bearings are common basic components in rotating machinery. During the operation of the bearing, the rolling slips, resulting in contact sliding friction between it and the raceway, which in turn causes wear in the rolling element and increase in the radial clearance of the bearing. The increase in clearance also affects the stiffness of the bearing, which in turn affects the natural frequency and fatigue life of the bearing. At present, there are few studies on the influence of bearing wear (variation of clearance) on life. In this paper, the finite element model based on the theory of contact mechanics is established for the angular contact ball bearing with medium- and high-speed rotation, and the mechanical properties and fatigue life influenced by the internal action of the bearing are analyzed. The effects of radial load and deflection angle on the mechanical properties and fatigue life of the bearing are also studied. Based on the analysis results of bearing contact mechanical properties and clearance changes, the calculation method of bearing life under rolling element wear is established. The influence of the variation of clearance and preload clearance on bearing life is analyzed, and the optimal preload is obtained. The research results of this paper can provide a theoretical basis for optimizing the installation of angular contact ball bearings, reasonably determining the service conditions, and prolonging the service life of bearings, which is necessary for engineering practice. [ABSTRACT FROM AUTHOR]

Affected by the service environment, the actual service conditions of rail steel are complex, and the safety evaluation methods are limited. In this study, the fatigue crack propagation in the U71MnG rail steel crack tip was analysed by means of the DIC method, focusing on the shielding effect of the plastic zone at the crack tip. The crack propagation in the steel was analysed based on a microstructural approach. The results show that the maximum value of stress of the wheel–rail static contact and rolling contact is in the subsurface of the rail. The test grain size of the material selected along the L–T direction is smaller than that in the L–S one. Within a unit distance, if the grain size is smaller, the number of grains or grain boundaries will be greater so that the driving force required for a crack to pass through the grain boundary barriers will be larger. The Christopher–James–Patterson (CJP) model can well describe the contour of the plastic zone and can well characterize the influence of crack tip compatible stress and the crack closure effect on crack propagation under different stress ratios. The crack growth rate curve at the high-stress ratio is shifted to the left relative to the low-stress ratio, and the crack growth rate curves obtained under different sampling methods have good normalization. [ABSTRACT FROM AUTHOR]

The friction and wear performance of high-performance bearings directly affects the accuracy and maneuverability of weapons and equipment. In this study, high-speed, high-temperature, and heavy-load durability experiments of weapon bearings were carried out, and their wear properties (i.e., surface wear, metamorphic layer, scanning electron microscopy/energy-dispersive spectroscopy (SEM/EDS), residual stress, and retained austenite) were analyzed in multiple dimensions. The results showed the following: (1) The experimental temperature of the serviced front-end bearing is always lower than that of the rear bearing. (2) The metamorphic layer of the serviced rear bearing (i.e., inner ring, outer ring, rolling body, and cage) > the metamorphic layer of the serviced front-end bearing > the metamorphic layer of the unserviced bearing. (3) The rolling body of the rear bearing at high experimental temperatures contains not only elemental O, but also elemental P and Sr. (4) In the EDS analysis of the rolling elements, with the migration from the "ball edge" to the "ball center", the elemental C in the rolling elements of serviced or unserviced bearings decreases slowly, while the elemental Fe content increases slowly. [ABSTRACT FROM AUTHOR]

The deformation and degradation behavior of unstabilized ballast and that stabilized with elastomer and geogrid was evaluated using process simulation test (PST) apparatus at various loading frequencies (f). The results indicated that elastomer has significantly reduced the extent of both vertical and lateral deformations of ballast. For example, elastomer reduced the extent of vertical settlement (Sv) in ballast from 22.76 to 9.83 mm, and the lateral deformation (ld) from 8.14 to 1.95 mm (f=15 Hz). It was also seen that the deformation and degradation of both stabilized and unstabilized ballast increased nonlinearly with the increase in the applied loading frequency (f). Further, the beneficial effect of elastomer in restraining the lateral flow of ballast was seen over the entire depth of treated ballast, unlike the geogrid, whose efficiency was maximum at its placement location and then reduced at farther locations. Moreover, elastomer has significantly enhanced the resilient modulus (Mr) and damping ratio (D) of ballast when compared with geogrid-reinforced ballast. For example, the elastomer increased the Mr and D of ballast by 25.9% and 66.6%, respectively, in comparison with an increment of only 15.1% and 25.3% in the case of geogrids (f:15 Hz). The Mr and D of ballast were found to be influenced by the effectiveness of the ballast stabilization technique in reducing lateral displacements. Additionally, elastomer has significantly reduced the vertical stress (σv) at the ballast–subballast interface by 34%. Further, elastomer was found to be more efficient than the geogrid in reducing the dynamic amplification factor (DAF) at any loading frequency. Similarly, elastomer reduced the breakage of ballast by 71% compared with the 40% of geogrid reinforcement (f=15 Hz). [ABSTRACT FROM AUTHOR]

Next generation rolls such as super-cermet rolls and all-ceramic rolls can be only manufactured as sleeve rolls, although the circumferential slippage appears at the shrink-fit interface. In this study, the fatigue strength of the sleeve roll is evaluated by applying the load shifting method on the fixed roll to realize the local slip accumulation during roll rotation. The simulation shows that the fatigue-inducing stress amplitude remains constant although the accumulated slip amount increases. Based on those results, the fatigue strength of standard rolling rolls is estimated considering the slip defect. The defect dimension can be characterized by the root area parameter and the value area =1254 μ m can be estimated from smaller roll experimental results and the previous report for larger diameter sleeve rolls. The results show that in the absence of slip damage, the fatigue strength of sleeve rolls is not much lower than that of solid rolls without shrink-fit. [ABSTRACT FROM AUTHOR]

The analysis of rail/wheel sliding friction heat is a very important research field. The numerical simulation is often adopted to calculate the friction heat, and experimental method is relatively few. In this paper, an experimental machine is designed to simulate the rail/wheel sliding contact. At the same time, a rail/wheel contact wear model and a friction heat transfer model are established. The characteristics of temperature on rail/wheel sliding contact are analyzed by experimental test and numerical calculation. The research results show that the temperature rise of wheel and rail is quick in the initial sliding contact stage, then gradually slows down. The temperature of wheel is higher than that of rail at the same depth from the contact surface. In the initial sliding stage, the wheel temperature rises faster than the rail temperature, which is related to the size of contact surface and the concentration degree of friction heat. Moreover, the results of this paper show that the temperature values of the rail/wheel obtained through experimental test and numerical calculation are in good agreement. The experimental and numerical calculation methods used in this article can be adopted to analyze the contact problems of other sliding friction pairs. [ABSTRACT FROM AUTHOR]

Vehicle-track interaction in a switch panel diverging route is studied with a focus on the way its components may interact in the lateral direction. Taking one of the cases of S&C benchmark as the base model, several variants of the co-running track model are considered. In the first series of simulation, the effect of the lateral separation of the switch rail and stock rail is investigated, showing that only small differences are found in terms of wheel/rail forces between a track model where both rails are coupled, and one where they are free to move with respect to one another. Only transient effects are visible at the beginning and at the end of the two-point contact on both rails. While small, these differences can have some influence in terms of rolling contact fatigue and wear prediction. In the second series of simulation, co-running track models are developed including the baseplate and taking into account such effects as switch rail/stock rail contact at the undercut plane and dry friction. Significant changes are observed in the load distribution within the switch panel. Conclusions should be consolidated through experimental field measurement and using more realistic track models, e.g. discretely supported rail beam models. [ABSTRACT FROM AUTHOR]

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

The ANSYS finite element software is introduced to simulate the cooling efficiency and thermal conductivity of the internal structure of the roll to study the influence of cooling water temperature, flow rate and aluminum melt on the roll temperature field and thermal conductivity. The research results show that in the process of casting and rolling, the aluminum melt is in contact with the rolls in the casting and rolling area, where the maximum temperature of the rolls is 520 °C. The temperature of the roll is gradually reduced to 40 °C, and then the roll continues to rotate until it enters the casting and rolling area, and the cycle is repeated. The reduction of the cooling water temperature could not significantly improve the roll temperature field. The increase of the cooling water flow rate can reduce the temperature field of the cooling water channel in the roll core. The temperature of aluminum melt at the exit of the casting nozzle can significantly increase the temperature field of the roll and the rolling temperature of the aluminum melt at the center of the roll gap, but it does not affect the temperature distribution at the exit of the roll gap after the aluminum melt is cooled by the roll. [ABSTRACT FROM AUTHOR]

Aiming at the problem of low control accuracy caused by nonlinear disturbances in the operation of the PLS-160 wheel–rail adhesion test rig, a linear active disturbance rejection controller (LADRC) suitable for the wheel–rail adhesion test rig was designed. The influence of nonlinear disturbances during the operation of the test rig on the control accuracy was analyzed based on SIMPACK. The SIMAT co-simulation platform was established to verify the control performance of the LADRC designed in this paper. The simulation results show that the speed and creepage errors of the test rig under the control of the LADRC met the adhesion test technical indicators under four different conditions. Compared with the traditional PID controller, the creepage overshoot and response time with the LADRC were reduced by 1.27% and 60%, respectively, under the constant creepage condition, and the stability recovery time was shorter under the condition of a sudden decrease in the adhesion coefficient. The LADRC designed in this paper shows better dynamic and anti-interference performance; therefore, it is more suitable for a follow-up study of the PLS-160 wheel–rail adhesion test rig. [ABSTRACT FROM AUTHOR]

With the increasing applications of the planetary roller screw mechanism (PRSM) in mechanical systems particularly machine tools, a comprehensive mathematical model is required to define the kinematic characteristics and relations of the PRSM, such that its performances can be predicted for reliability analysis and design of machine tools. In this paper, the influences of machining and assembly errors on the motion characteristics of the PRSM are analyzed, and the kinematic model of the PRSM is established considering runout errors and elastic deformation. The planetary roller screw mechanism can be considered as a spring-mass system for analysis of the elastic deformation of the ball screw's thread under inertial force. For the spring-mass system, adjacency matrix is introduced to define the relationships between the elastic displacements of the joints and the deformations of the elements. Then, by considering the balance of force and the coordination of deformation, the nonlinear motion model of the double-nut roller screw is established. The effectiveness of the proposed model is verified by comparing the analytical results with the experimental data. [ABSTRACT FROM AUTHOR]

Radial clearance critically affects journal bearing performance, specifically the lubrication performance. This study investigates the lubrication characteristics of a journal bearing with adjustable radial clearance and compares the dynamic behavior of the bearing under laminar and turbulent flow regimes. The adjustable bearing exhibits two states of oil film pressure at different radial clearances. When the radial clearance is reduced from 100%cr to 80%cr, the oil film pressure is present only on the lower bearing bush; after being reduced to 70%cr, the upper bearing bush achieves effective lubrication; and after reduction from 70%cr to 30%cr, the oil film pressure increases more than six-fold. The turbulent flow model of the clearance adjustable bearing is then established considering the lubricant flow state, and the turbulence correction factors for different flow states are calculated. The journal bearing exhibits better lubrication characteristics under laminar than under turbulent flow conditions, and in some operating conditions, the stable velocity range calculated according to laminar flow theory may become unstable in turbulent flow conditions. Therefore, applying turbulence assumptions to design the operating speed range of rotating machinery under such conditions yields a greater safety threshold, which can reduce the risk of instability. The stability of the rotor bearing system is closely related to the radial clearance, and reducing the radial clearance will improve the stability of the system. In the turbulent flow state, the oil film pressure changes drastically, thus reducing the system stability. Moreover, the larger the radial clearance of the bearing, the more prominent the turbulence effect. Thus, reducing the bearing clearance prevents drastic changes in oil film pressure and improves the stability of the system. [ABSTRACT FROM AUTHOR]

This research paper reviews the recent works on the rolling contact fatigue of rail wheels. The topic covered includes the mathematics equations of rail-wheel contact stress and fatigue, RCF defects in the rail, the development of cracks, and the strategies used to reduce the rate of RCF defects. Therefore, the main understandings of RCF as they currently stand are crucial for the improvement and mitigation on rail fatigue failures in the future. This research paper has not been published yet and has not been discussed yet by the Malaysia Railway Network. [ABSTRACT FROM AUTHOR]

This investigation integrates an alternative fully-parameterized approximation of nonlinear wheel/rail interaction into a simplified vehicle model, and a two-parameter Hopf bifurcation analysis is conducted to reveal the influence of the wheel/rail contact geometry and secondary suspension parameters for high-speed rail vehicles. The bifurcation diagram is compared among the 6 DOFs bogie model, linear and nonlinear 7 DOFs vehicle model, nonlinear 17 DOFs vehicle model, and 3D full DOFs vehicle model. It shows that the nonlinear 7 DOFs vehicle model can meet the requirement of both carbody hunting and bogie hunting simulations. 6 DOFs bogie model can only be used in bogie hunting bifurcation analysis. Linear vehicle model would bring errors in either critical speed or limit circle magnitude. The divergences in the linear terms of rolling radius and contact angle polynomials are significant enough in field operation to cause a noticeable difference in Hopf bifurcation speed. Attention shall be paid to the shape of equivalent conicity and contact angle curve. The crucial parameters to the Hopf bifurcation include the series stiffness and damping coefficient of the yaw damper and the lateral damper damping. However, the requirement of suspension parameters for stability can conflict in carbody hunting and bogie hunting cases. [ABSTRACT FROM AUTHOR]

Vision is the main component of current robotics systems that is used for manipulating objects. However, solely relying on vision for hand−object pose tracking faces challenges such as occlusions and objects moving out of view during robotic manipulation. In this work, we show that object kinematics can be inferred from local haptic feedback at the robot−object contact points, combined with robot kinematics information given an initial vision estimate of the object pose. A planar, dual-arm, teleoperated robotic setup was built to manipulate an object with hands shaped like circular discs. The robot hands were built with rubber cladding to allow for rolling contact without slipping. During stable grasping by the dual arm robot, under quasi-static conditions, the surface of the robot hand and object at the contact interface is defined by local geometric constraints. This allows one to define a relation between object orientation and robot hand orientation. With rolling contact, the displacement of the contact point on the object surface and the hand surface must be equal and opposite. This information, coupled with robot kinematics, allows one to compute the displacement of the object from its initial location. The mathematical formulation of the geometric constraints between robot hand and object is detailed. This is followed by the methodology in acquiring data from experiments to compute object kinematics. The sensors used in the experiments, along with calibration procedures, are presented before computing the object kinematics from recorded haptic feedback. Results comparing object kinematics obtained purely from vision and from haptics are presented to validate our method, along with the future ideas for perception via haptic manipulation. [ABSTRACT FROM AUTHOR]

This study clarifies a doubt on the validity of using roller tests rigs for evaluating the dynamics of rail vehicles running on straight tracks. The tested vehicle has no forward speed and stands on a wheel equipped with rails of which the tangential constant velocity, V, simulates the real vehicle velocity. Using this test method assumes that bogie dynamics depend only on contact forces. Recently, ref. [1] argue that, due to the lack of forward speed, roller test rigs are lacking inertial 'centrifugal' forces. As these forces cannot be calculated on test rigs where the vehicle forward speed is zero, hence comes the validity question. We answer by developing an imaginary scenario where a mass, representing a railway wheelset, is associated to a spring forming a pendulum oscillating along the normal to the vehicle speed. The paper demonstrates that the calculated inertial forces are split into two forces, normal and tangential to the trajectory, and that, although each one of these two forces depends on V, only their resultant, which does not depend on V, has a mechanical meaning and does not contradict classical mechanics which support the validity of test rigs. A numerical example supports this conclusion. [ABSTRACT FROM AUTHOR]

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

Wear characteristics of an (Mo–Nb–Ta–V–W)C high‐entropy carbide were investigated using ball‐on‐flat technique. The experimental material with a high relative density of 99.0%, single phase, average grain diameter of 10.7 μm, and nanohardness of grains 28.6 GPa was prepared by ball‐milling and two‐step field‐assisted sintering. The tribological test was realized during dry sliding in air with the SiC ball as tribological partner at applied loads 5, 25, and 50 N. The microstructure, deformation, and damage characteristics were studied using scanning electron microscopy and confocal electron microscopy. The friction coefficient values during the test with 5 and 25 N were very similar and stable, with a value of approximately.4, whereas during the test with 50 N, it decreased from the value of.48–.42. The specific wear rate increased with increasing load from 3.71 × 10–7 mm3/N m at 5 N to 2.59 × 10–6 mm3/N m at 50 N. The dominant wear mechanism was mechanical wear with intensive grains pullout, fracture, and powder formation, without visible tribochemical reactions and tribo‐layer formation. The wear rate decreased due to the created rolling contacts among the tribopartners thanks to the hard and spherical nanopowders present. [ABSTRACT FROM AUTHOR]

Purpose: Herringbone groove thrust bearings are typically used in high-speed, light-load applications, such as spindle motors for hard disk drives. In the past researches, the effect of shaft misalignment was little considered. This study aims to reveal effects of shaft misalignment on the microscopic flow regime in the water-lubricated herringbone groove thrust bearing. Design/methodology/approach: The liquid film in a thrust herringbone groove bearing was investigated by computational fluid dynamics. The effects of micro-grooves on the flow field were carefully explored. Two-dimensional liquid films at four different sites were examined for obtaining the rich flow field properties. Findings: The distributions of pressure, temperature and water vapor volume fraction were obtained, the micro hydrodynamic effects were formed by the herringbone grooves and the effects of the shaft misalignment on lubrication and sealing performance could be found. Originality/value: The influence of misalignment on the herringbone groove thrust bearing performance was investigated in detail. The obtained results could give the reference guideline for the bearing design. [ABSTRACT FROM AUTHOR]

This work proposes a systematic approach to detect and classify bearing faults using vibration signals under varying speeds. The proposed approach consists of several steps, such as segmentation of signal consisting of maximum fault relevant information and extraction of features less influenced by varying speeds, and develop a machine learning model for online classification of bearing faults. Bearing when operating under time-varying speeds, the most critical and challenging step, is the demodulation of non-stationary and nonlinear vibration signals exhibiting severe modulations. The empirical wavelet transformation (EWT) algorithm has been used to decompose the raw signal into multiple mode functions (MFs), thereby detecting faults. However, these MFs contaminated by vestigial noise, when processed, mislead the detection of incipient bearing faults, thereby reducing EWT performance. Hence, this study addresses this by proposing the selection of the most impulsive MF for varying speed by estimating instantaneous frequency, which lies near bearing characteristic defect frequencies, thereby eliminating the possibility of vestigial noise being processed. Further, ten entropies, root-mean-square, and kurtosis are computed from the selected MF for statistical analysis. The results of the proposed approach are compared with the ensemble empirical mode decomposition to highlight the capabilities. Statistically significant fault discriminating features are identified using the Kruskal–Wallis test. These identified features are subsequently utilized by the Random Forest classifier. Thus, it has resulted in higher accuracy in detecting and classifying the different faults trapped by severe modulations. [ABSTRACT FROM AUTHOR]

This work proposes a systematic approach to detect and classify bearing faults using vibration signals under varying speeds. The proposed approach consists of several steps, such as segmentation of signal consisting of maximum fault relevant information and extraction of features less influenced by varying speeds, and develop a machine learning model for online classification of bearing faults. Bearing when operating under time-varying speeds, the most critical and challenging step, is the demodulation of non-stationary and nonlinear vibration signals exhibiting severe modulations. The empirical wavelet transformation (EWT) algorithm has been used to decompose the raw signal into multiple mode functions (MFs), thereby detecting faults. However, these MFs contaminated by vestigial noise, when processed, mislead the detection of incipient bearing faults, thereby reducing EWT performance. Hence, this study addresses this by proposing the selection of the most impulsive MF for varying speed by estimating instantaneous frequency, which lies near bearing characteristic defect frequencies, thereby eliminating the possibility of vestigial noise being processed. Further, ten entropies, root-mean-square, and kurtosis are computed from the selected MF for statistical analysis. The results of the proposed approach are compared with the ensemble empirical mode decomposition to highlight the capabilities. Statistically significant fault discriminating features are identified using the Kruskal–Wallis test. These identified features are subsequently utilized by the Random Forest classifier. Thus, it has resulted in higher accuracy in detecting and classifying the different faults trapped by severe modulations. [ABSTRACT FROM AUTHOR]

A three-dimensional wheel–rail rolling contact model (3D WRRCM) developed using the explicit finite element method (FEM) can be used to analyze the dynamic performances of wheelsets and tracks while considering the wheelset rotation and translation, as well as the real wheel–rail contact mechanism. When using the FEM with static initialisation (traditional model), the first step is to calculate the static wheel–rail displacement, strain, and stress when applying axle loading on the wheel and neglecting the wheelset rotation and translation. Then, using these results as the initial conditions, the dynamic wheel–rail displacement, strain, and stress are calculated while considering the wheelset rotation and translation by adopting the explicit dynamic solution method. However, obtaining a solution using this traditional method is time consuming, and the solution can be divergent because of the impulse produced by the suddenly increasing wheelset rotation when proceeding from the initial condition to the dynamic. The optimised method developed in this study can solve this problem. A comparison of the results from the traditional and optimised methods reveals that in the optimised method, the softer initial impulse effectively shortens the track length needed for the calculation and improves the solution efficiency. [ABSTRACT FROM AUTHOR]

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

Combined influence of temperature and mechanical deformations define the resulting contact stresses, heat flow, and rolling loss at the tire–pavement contact. In this study, the thermomechanical coupling of a hyperviscoelastic tire with a deformable pavement layer revealed the impact and extent of temperature influence on the hysteretic loss of a rolling tire. A scheme to predict the three-dimensional contact stress distribution was established that incorporated the thermomechanical interaction between a rolling hyperviscoelastic truck tire and a deformable pavement layer. The fully coupled thermal-stress model addressed two distinct yet intertwined perspectives: (1) establishing a thermomechanical database and prediction tool to generate contact stresses as inputs for pavement structural design, and (2) quantifying the associated rolling loss at the tire–pavement interaction that relates to tire design configurations and environmental impacts. Differences in the resulting contact stresses and rolling energy loss were observed between imposing uniform and nonuniform temperature profiles. Both the range and magnitudes of stresses throughout the tire–pavement contact imprint changed drastically as varying temperature profiles were implemented. Ranking the influence of thermal boundary conditions, the ambient temperature induced the highest impact on the dissipation energy and change in contact stress distribution, followed by the road and inner tire surface conditions. Moreover, the global hysteretic loss within the tire as myriad temperature profiles were imposed did not change significantly; however, the creep dissipation observed within the contact imprint revealed a higher disparity. In this study, a finite-element model was established to simulate a free-rolling truck tire over a pavement layer and determine the combined influence of temperature and loading on the three-dimensional contact stresses and hysteretic loss. The thermomechanical interaction between the truck tire and pavement layer impacted both the range and magnitude of the contact stresses, wherein differences were observed between imposing uniform and nonuniform temperature profiles. Particularly, the ambient temperature had the highest impact on the contact stress distribution and dissipation energy, in contrast to the level of influence from the pavement surface temperature and internal tire air temperature. In lieu of complex models, nonlinear regression equations were developed as a simple means to generate three-dimensional contact stress inputs for pavement analysis. Future model improvements and considerations may include other rolling conditions, such as braking, accelerating, or cornering conditions; temperature-dependent tire-inflation pressure and interface friction; influence of air and sun through convection and radiation along with daily temperature cycles; and a viscoelastic asphalt pavement layer. [ABSTRACT FROM AUTHOR]

For high-speed, heavy-load gear units, the meshing tooth surfaces are generally under the mixed lubrication state, which is crucial for gear pitting or micro pitting damage. To clarify the effects of lubrication state on tooth pitting damage, carrying out both numerical and experimental studies on the contact severity of gears under different lubrication states is necessary. In this paper, a 3D line-contact elasto hydrodynamic lubrication model considering fractal surface roughness was developed and used to investigate the lubrication characteristics of involute gears. Both the distributions of pressure and film thickness fluctuated under the rolling contact of rough surfaces. The fluctuations became more substantial with the increase of load and roughness. Furthermore, from the calculated film thickness ratio λ, the contact of gear tooth surfaces with a fractal roughness of Ra = 0.8 µm was always under full lubrication state (λ > 1). When the roughness was increased to Ra = 3.2 µm, the contact was first transmitted into the mixed lubrication state (0.2 < λ < 1) under the load of 1000 N*m and finally deteriorated to boundary lubrication state (λ < 0.2) under the load of 2000 N*m. The boundary lubrication state that occurred under the contact of highly rough surfaces could induce the formation of gear pitting damage. The contact fatigue test showed the gear tooth surface roughness increased from 0.7 µm to around 2.7 µm after 8 million running cycles and then suffered pitting failure after another 2 million cycles, which was consistent with the simulation analysis prediction. [ABSTRACT FROM AUTHOR]

Friction modifiers (FM's) are substances deliberately applied to the top‐of‐the‐rail in the field in order to control the traction coefficient. In this work, two FM's, a commercial (FM1) and a custom‐made (FM2), and a gauge lubricant (CGL) were evaluated in the laboratory using rheological and tribological tests. Two rheological tests were done: oscillatory (frequency and strain sweeps) and flow tests (viscosity vs. shear rate). Tribological tests were done in a twin disk machine to obtain the traction coefficient under different slip values. Retentivity tests were also done in the same machine. Several physical–chemical tests were also done to characterise the products. The results of rheological tests showed that there are notable differences that can influence the performance of FMs. From the studied materials, the FM2 product tends to be more viscous even for high‐shear rates. The tribological tests showed that the traction coefficient is different for all the studied materials and changes from 0.15 to 0.45 depending on the creepage. The retentivity of FM2 is 1.9 times higher than FM1. The results show a good correlation between the rheological behaviour and the coefficient of traction and retentivity. [ABSTRACT FROM AUTHOR]

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

The abrasive belt grinding process is applied to grind aero-engine blades benefiting from the elastic contact between the tool and workpiece. The local material removal is difficult to be accurately controlled, resulting in poor surface integrity. A better understanding of the relations between key process parameters and the material removal is needed. In this study, a physical simulator of the abrasive belt grinding process was developed. Different contact wheel hardnesses and contact forces were applied to grind the titanium alloys. A finite element model of multi-abrasive grinding was established to predict the material removal. The characteristics of the stress distribution on the rubber wheel under the dynamic contact state of abrasive belt grinding were obtained. The results show that the contact force has a significant effect on material removal when the contact force is less than a critical value. When the contact force exceeds the critical value, the hardness of the rubber wheel has a more significant effect. The changes on material removal obtained by the finite element model are consistent with the experimental results within the range of presented process conditions. This study provides a basis for selecting grinding contact force and contact wheel hardness. • A physical simulator was developed for investigating this compliant grinding process. • A numerical model of local material removal was established. • Influence of rubber hardness on material removal is nonlinear with pressure variation. [ABSTRACT FROM AUTHOR]

The present work is a contribution in improving the hydrodynamic method proposed by Li et al. (Steel Res Int 87(9999) 88:2053–2059, 2016; Int J Adv Manuf Technol. Springer-Verlag, London, 2016) used to predict the pressures and the rolling speeds during hot rolling of aluminum strips. The hydrodynamic model gives good prediction. However, it is based on empirical coefficients which must be identified for each rolling case. Therefore, a critical analysis of the Si Li's method has been first made and then a methodology for improving it has been presented. The improvement consists in coming out of the empiric coefficients and considering the variation of viscosity as a function of pressures. Finite element simulations have been conducted to validate the improved method. Much reliable results have been obtained that are in good agreement with the experimental data. The proposed approach is rapid and much easier to use within the industrial application. [ABSTRACT FROM AUTHOR]

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

Lubrication is essential to minimize wear and friction between contacting surfaces in relative motion. Oil based lubricants are often enhanced via polymer additives to minimize self-degradation due to the shear thinning effect. Therefore, an accurate estimate of the load carrying capacity of the thin lubricating film requires careful modeling of shear thinning. Available models such as the generalized Reynolds equation (GR) and the approximate shear distribution have drawbacks such as large computational time and poor accuracy, respectively. In this work, we present a new approach, i.e., the modified viscosity (MV) model, based on calculating the strain rate only in one point along the vertical direction. We investigate, for both MV and GR, the load, the maximum pressure, and the computational time for (i) sliding (non-cavitating) contacts, (ii) cavitating, and (iii) squeezing contacts. We observe that the computational time is reduced (i) considerably for non-cavitating sliding and rolling contacts and (ii) by several orders of magnitudes for cavitating and squeezing contacts. Furthermore, the accuracy of MV is comparable with the GR model within an appreciable range of bearing numbers. Finally, for each type of boundary motion, we have determined the optimal vertical location to calculate the shear strain rate for MV; while this optimal value is close to half the height of the contact for sliding configurations, for rolling dominated and squeezing contacts it is around one quarter (or three quarter) of their height. We finally provide an analysis to a priori estimate the optimal location of the strain rate. [ABSTRACT FROM AUTHOR]

Low-frequency hunting problems of high-speed railway vehicles frequently occur due to the complex operating environment and degradation of wheel–rail contact conditions, which significantly affect the running safety and ride comfort of high-speed trains (HSTs). This paper presents a numerical investigation of the influence of aerodynamic loads on the carbody low-frequency hunting behaviors of HST. Considering the effect of aerodynamic loads, a multi-body system dynamics model for a HST train is formulated and applied to reproduce the carbody low-frequency hunting behavior. The influence of aerodynamic loads and wheel–rail contact conditions on the nonlinear stability of HST is analyzed. The range of aerodynamic coefficients of different aerodynamic loads which can stimulate the low-frequency hunting behavior of HST is proposed. The results show that the aerodynamic loads have a prominent effect on the nonlinear stability of HSTs. The low-frequency hunting motion of the HST tail car can be motivated by the lift airflow generated during service operation with a high traveling speed. The running stability of HSTs is more easily influenced by the aerodynamic loads when wheels are reprofiled. [ABSTRACT FROM AUTHOR]

When trains pass through damaged switch rails, rail head damage will change wheel–rail contact states from rolling frictions to unsteady contacts, which will result in impact vibrations and threaten structural safeties. In addition, under approaching and moving away rolling contact excitations and complex wheel–rail contacts, the non-stationary vibrations make it difficult to extract and analyze impact vibrations. In view of the above problems, this paper proposes a variational-mode-decomposition (VMD)-spectral-subtraction (SS)-based impact vibration extraction method. Firstly, the time domain feature analysis method is applied to calculate the time moments that the wheels pass joints, and to correct vehicle velocities. This can help estimate and confine impact vibration distribution ranges. Then, the stationary intrinsic mode function (IMF) components of the impact vibration are decomposed and analyzed with the VMD method. Finally, impact vibrations are further filtered with the SS method. For rail head damage with different dimensions, under different velocity experiments, the frequency and amplitude features of the impact vibrations are analyzed. Experimental results show that, in low-velocity scenarios, the proposed VMD–SS–based method can extract impact vibrations, the frequency features are mainly concentrated in 3500–5000 Hz, and the frequency and peak-to-peak features increase with the increase in excitation velocities. [ABSTRACT FROM AUTHOR]

In order to understand the influence of FKM surface morphology on wetting performance and tribological properties under high temperature conditions. According to the phenomenon of reducing resistance in the water of natural fish scales, we prepared the FKM with a convex structure using a 2800 mesh screen (which is called 2800FKM), by hot pressing and template replication, based on the fish-scales bionic structure. At 25 °C and 150 °C, the contact angle and rolling angle of the 2800FKM surface were measured, and then we evaluate the bounce behavior and self-cleaning performance of the 2800FKM surface. Finally, under the condition of dry friction and grease lubrication friction, the wear mechanism of 2800FKM was studied by SEM. The results show that compared with FKM, 2800FKM has excellent wetting performance (Contact angle = 143.51°) and heat retention rate (98.89%), and self-cleaning. Compared with FKM, 2800FKM has better anti-wear and antifriction performance under dry friction conditions, and no noticeable wear marks are found under grease lubrication conditions. The main factor of 2800FKM's excellent wetting performance and anti-wear and antifriction function is the fish scale bionic structure. The preparation of 2800FKM provides a new idea for exploring wear-resistant materials with bionic fish scale structure. [ABSTRACT FROM AUTHOR]

Relative to the Hertzian theory, the non-Hertzian contact model (NHM) can better reflect the contact characteristic between wheel and rail in railway vehicle dynamics simulation. In this paper, an optimal wheel-rail tangential contact model is determined for vehicle dynamics simulation. First, based on i) the modified Kik–Piotrowski (MKP) contact model, ii) four different ellipse-equivalent methods, and iii) the modified FASTSIM model or modified FaStrip model, eight NHMs are proposed. Then, taking the Kalker's variational method (KVM) as a reference, the computational accuracies of the eight NHMs for calculating the linear creep coefficient and the tangential forces for the typical tangential contact scenarios are compared. NHM II, that is, the model coupled with the MKP model, the ellipse-equivalent method adopted in the Kik–Piotrowski (KP) model, and the modified FaStrip model, shows the best computational accuracy. Finally, the traditional Hertzian & FASTSIM model, the NHM II model, and KVM model are applied to the vehicle-track coupled dynamics simulations, and the dynamics response of a high-speed train running on a slab track is calculated by different contact models. The comparison results show that the NHM II model exhibits better agreement with the KVM compared with the Hertz & FASTSIM model. [ABSTRACT FROM AUTHOR]

Wheel wear is a natural phenomenon of wheel–rail rolling contact during vehicle operation. The non-uniform wear in lateral and circumferential directions is normally occurred on wheels. The lateral non-uniform wear will lead to the unexpected hollow wear which can cause flange to flange vibration at low-frequency band, and the circumferential non-uniform wear will result in the vertical vibration which is the originate from the polygon phenomenon. These two forms of wear are coupled to each other on wheels and affect the dynamic behaviours of wheel–rail system. In this paper, a wheel–rail contact dynamics model which includes the 3D geometric shape of wheel profile is established and employed to vehicle system dynamics. The results show that the contact mechanical properties of wheel–rail are greatly affected by the 3D wheel profile. The low-frequency vibration of wheelset caused by hollow wear and the high-frequency vibration by polygonised wear are coupled, which increase the vibrational acceleration of wheel–rail system and even made for the main problem of the periodic separation of wheel and rail and aggravate the wear of wheel polygon. [ABSTRACT FROM AUTHOR]