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The development results of a single-point contact system set up as a pendulum to study the laws of rolling resistance to contacting bodies at a distance significantly reduced compared to the elastic contact spot size. The designed device uses a physical pendulum sustained by only one ball on a flat polished surface. The problem of stability of the pendulum swing plane is solved. A phenomenological theory of rolling resistance is described. The surface tension of solids on the contact zone, parameters of the frequency-independent internal friction and the pressure of the adhesion forces are found. [ABSTRACT FROM AUTHOR]

In railway operation, the sanding process is used to overcome low adhesion conditions in the wheel–rail contact. In the literature, previously conducted research has been experimental, e.g., measuring adhesion coefficients (ACs) under different contact conditions (dry, wet, ...) or applying different sands. Under dry conditions, sanding can reduce measured ACs, while under wet conditions different types of rail sand can leave ACs unchanged or increase adhesion. Despite active research, the physical mechanisms causing the change in ACs under sanded conditions are still poorly understood. A possible remedy is the development of advanced models of sanding including local effects. As a basis for such a model, this study presents experimental results concerning single grain crushing behaviour of two types of rail sand under dry and wet contact conditions. Firstly, initial breakage behaviour is investigated with focus on the particle fragments' size and spread as only fragments within the running band are available to influence the AC during roll-over. Secondly, single grain crushing tests are conducted under realistic wheel–rail load showing the formation of solidified clusters of sand fragments, as well as their size and thickness. This information is important for understanding mechanisms and for future physics-based modelling of the sanding process in wheel–rail contacts. [ABSTRACT FROM AUTHOR]

Wheeled omnidirectional mobile robots have been developed for industrial and service applications. Conventional research on Omni wheel robots has mainly been directed toward point-symmetric wheel arrangements. However, more flexible asymmetric arrangements may be beneficial to prevent tipping over or to make the robot more compact. Asymmetry can also be the result of a motor/wheel failure in a robot with a redundant configuration; in this case, it may be possible to continue operations, but with an asymmetrical arrangement. For controlling such asymmetric arrangements, it is necessary to consider the moment of propulsive force generated by the wheels. Since it is difficult to measure the propulsive force accurately, in this work we model propulsive forces as being proportional to the ground speed of the wheels. Under this assumption, we estimated the robot's behavior in an asymmetric wheel configuration by considering the balance of the velocity moment, which is the moment of the wheel's ground speed. By verifying the robot's behavior with various wheel configurations, we confirmed experimentally that the sum of the velocity moments affects the straightness of the robot and allows us to improve the design of asymmetric wheel arrangements and control during wheel failures. [ABSTRACT FROM AUTHOR]

Numerical analyses of the roller-raceway contact have been carried out in a spherical roller bearing using frictional contact models of different complexity. The models used in the study include an implementation of Kalker's exact contact theory named CECT (Conformal Exact Contact Theory) and detailed Finite Element models. The adequacy of the more simplified contact solutions is assessed by contrasting them with the solutions obtained with themore comprehensive models. Additionally, the use of the exact contact theory, well known in the wheel-rail application, is demonstrated in contact mechanics analyses in rolling bearings, describing relevant details of its implementation for this application. Situations with different normal loads and friction levels have been analysed, and two distinct steady equilibrium configurations of the roller have been identified. [ABSTRACT FROM AUTHOR]

Featured Application: This study proposes a heat generation model for selecting an energy-efficient design for a rolling bearing cage. Several aspects must be considered in the design of rolling bearing cages. One of the most important considerations relates to studying and developing a stationary approach for solving problems of heat and mass transfer during convection. In this context, this paper proposes, among other achievements, the development and validation of a model of heat generation that is used, as the basis for an energy-efficient cage design in the context of the roller bearings of axle boxes for rail transport. The forces of interaction of the cage with the bearing parts are determined. The energy-efficient design of the cage is performed with modified friction surfaces in the form of convex contours of the pockets and micro-hollows on the surfaces of the pockets and support rings. On the basis of a flat model, of the interaction between the cage and the bearing parts, the pressure forces on the driving and driven rolling elements in the zone of radial loading are determined. The frictional moment of the bearing has been determined based on the integral design of the cage without taking into account lubrication during the interaction of the cage with the jumpers and with the sides of the basing ring. The calculation of the temperature gradient with standard and improved designs of bearing cages has been performed while taking air blowing into account; results showed a decrease in the average level and growth rate of the bearings' temperature gradient with an energy-efficient cage design. Based on the obtained results, and on the developed heat generation model, a systematic approach for energy-efficient design of rolling bearing cages is proposed. The proposed approach, as well as the respective developed models, were validated by obtaining and analyzing the experimental results. [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]

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]

Intelligent fault diagnosis gives timely information about the condition of mechanical components. Since rolling element bearings are often used as rotating equipment parts, it is crucial to identify and detect bearing faults. When there are several defects in components or machines, early fault detection becomes necessary to avoid catastrophic failure. This work suggests a novel approach to reliably identifying compound faults in bearings when the availability of experimental data is limited. Vibration signals are recorded from single ball bearings consisting of compound faults, i.e., faults in the inner race, outer race, and rolling elements with a variation in rotational speed. The measured vibration signals are pre-processed using the Hilbert–Huang transform, and, afterward, a Kurtogram is generated. The multiscale-SinGAN model is adapted to generate additional Kurtogram images to effectively train machine-learning models. To identify the relevant features, metaheuristic optimization algorithms such as teaching–learning-based optimization, and Heat Transfer Search are applied to feature vectors. Finally, selected features are fed into three machine-learning models for compound fault identifications. The results demonstrate that extreme learning machines can detect compound faults with 100% Ten-fold cross-validation accuracy. In contrast, the minimum ten-fold cross-validation accuracy of 98.96% is observed with support vector machines. [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.

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]

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]

The application of polymer-based composite materials as bearing liner materials in eco-friendly water lubrication has received considerable attention owing to their superior tribological behaviors, corrosion resistance, and high damping characteristics, and their design flexibility can improve the bearing performances in response to the distribution of lubricant film pressure based on the regulation of elastic constants. However, the low viscosity and high density of water essentially cause thin-filmed lubrication accompanied by a low load-carrying capacity. Particularly, a high rotational speed enhancing the wedge effect induces turbulence and considerable inertial effect. Moreover, substantial elastic deformation of the composite bearing liners alters the formation of the lubricant film. In this study, we analyze a water-lubricated composite journal bearing system incorporating the turbulence, inertial effect, and elastic deformation of the bearing liner. Reynolds equation was modified considering the turbulence and inertial effect. The elastic deformation of the composite bearing liner was determined by solving the constitutive equation. The Reynolds equation and the constitutive equation were solved via the finite differencemethod and finite elementmethod, respectively. In addition, the analytical relation for the elastic deformation was derived that suitably eliminated the requirement of solving the constitutive equation. With the introduction of the primary parameters, Sommerfeld number, Reynolds number, and deformation coefficient, the relation of the normalized minimum film thickness with respect to the parameters was modeled based on the Gaussian regression model. Accordingly, we proposed the new optimal maximumload-carrying capacity boundaries that narrowed down the operating region compared to conventional boundaries. [ABSTRACT FROM AUTHOR]

Hot ring rolling is a method of forming ring products with large diameters in relation to the cross-sectional dimensions. This process is a complex incremental metal forming process. It is characterized by high dynamics and continuous change of shape of the rolled ring. Important process parameters are the rotational speed (and the peripheral speed dependent thereon) and the infeed speed of the main roll. In industry, the goal is to be as effi cient as possible, so it makes sense to use the highest possible speeds in the process. An important issue is to determine the ratio of the peripheral speed of the main roll to the infeed of that roll. If the ratio of these speeds is too low, the ring is distorted due to the occurrence of slippage between the tools and the ring being shaped. The objective of the research presented in this study was to determine the limiting ratio of infeed speed to peripheral speed of the main roll. Based on the tests conducted, a range of values for the ratio of the two speeds of the main roll at which the process can be performed properly was determined. [ABSTRACT FROM AUTHOR]

In response to the problems of low accuracy and poor noise immunity of the traditional fault diagnosis method for rolling bearing fault diagnosis due to the complex and variable operating conditions of rolling bearings and the large noise interference during bearing signal acquisition, a rolling bearing fault diagnosis model based on VMD–RP–CSRN is proposed. Firstly, the initial feature extraction of the bearing signal is carried out by variational modal decomposition (VMD), which is then converted into a two-dimensional image with fault features by recurrent plot (RP) coding, and then the feature images are input to a channel split residual network (CSRN) for feature extraction and fault classification. In order to verify the accuracy and noise immunity of the proposed method for the diagnosis of bearing faults under complex working conditions, experiments on the selection of parameters in the CSRN model were conducted on the bearing dataset of Jiangnan University, and experiments on the diagnosis of bearing faults under complex working conditions and noise immunity of CSRN were carried out and compared with other commonly used methods. The proposed bearing fault diagnosis method based on VMD–RP–CSRN combines VMD and RP to retain the fault features in the original signal to the maximum extent and stress the hidden features in the signal. The proposed channel split operation realizes the extraction of hidden features by selecting the main operating channel of the three-channel feature image, and makes more fault features participate in the feature extraction of the diagnosis model. The experimental results demonstrate that the proposed method is at least 1.2% better than the comparison method, and has better noise immunity. In addition, experiments on the fault diagnosis capability of the model with different data set sizes and the diagnosis of variable speed bearing data by the model show that the proposed method has better generalization performance and diagnosis capability. [ABSTRACT FROM AUTHOR]

The rolling element bearing is a fundamental component of any rotating machinery. During operation, wear debris and lubricant impurities create dents and bumps on the bearing raceway surfaces. Such localized defects produce transient vibration impulses at one of the bearing characteristic frequencies. Having a combination of multiple types of point defects on the raceway results in superimposed vibration patterns, which reduce the ability to recognize these defects' effects. In this paper, a 6-DOF dynamic model is developed to accurately investigate the vibration characteristic of a ball bearing with a multipoint defect comprising a dent and bump on its raceway surface. The model considers the effects of time-varying contact force produced due to defects, lubricant film damping, bearing preload, and the inertia effect of rolling elements. The simulation results reveal the vibration behavior of multipoint defect bearings. In addition, bearing vibration response is affected by the number of defects, the angle between them, and the type and size of each defect. Furthermore, it is challenging to predict bearing defects parameters such as the numbers, types, sizes, and angles between adjacent defects from acceleration signal analysis without jerk signal analysis. The validation of the model is proved using signals from the Case Western University test setup. [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]

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]

In the course of the electrification of powertrains, rolling element bearings are increasingly subject to electrical damage. In contrast to mechanically generated pittings, voltage-induced surface damage is a continuous process. Though several approaches for the description of the damage state of a bearing are known, a generally accepted quantification for the bearing damage has not been established yet. This paper investigates surface properties, which can be used as a metric damage scale for the quantification of the electric bearing damage progression. For this purpose, the requirements for suitable surface properties are defined. Afterwards, thrust ball bearings are installed on a test rig, with constantly loaded mechanically and periodically damaged electrically in multiple phases. After each phase, the bearings are disassembled, the bearing surfaces are graded and measured for 45 different standardized surface properties. These properties are evaluated with the defined requirements. For the ones meeting the requirements, critical levels are presented, which allow for a quantified distinction between grey frosting and corrugation surfaces. These values are compared with measurements presented in the literature showing that the identified surface properties are suitable for the quantification of electrical bearing damages. [ABSTRACT FROM AUTHOR]

The research on wheel–rail relationship includes the basic theoretical models and corresponding numerical methods of wheel–rail in rolling contact, geometric parameter matching and material matching of them, friction and wear, wheel–rail rolling contact fatigue, wheel–rail adhesion and noise. They are also key theoretical and technical problems of the high-speed train/track coupling system. The basic theoretical models of wheel–rail in rolling contact and the corresponding numerical methods are the basis and one of the basic means for solving other wheel–rail relationship problems. The other is the experimental means. Moreover, the modeling and analysis of coupling behavior of the train and track can only be realized by means of the wheel–rail rolling contact mechanics model and its corresponding numerical method. This paper mainly discusses some research work and achievements on high-speed wheel–rail relationship problems since China opened a high-speed railway system on a large scale. The discussions in this paper include the classic wheel–rail rolling contact theoretical models (analytical forms) and the modern wheel–rail rolling contact theories (numerical methods), their advantages and disadvantages, their application and future development direction of them. The reviewed research progress on the other wheel–rail relationships mainly expounds the thorny problems of the wheel–rail relationship encountered in the operation of China's high-speed railway, how to adopt new theoretical analysis methods, test means and take effective measures to solve these problems. It also includes research results of similar important reference values performed by international peer experts in related fields. Challenging and unsolved problems in high-speed wheel–rail relationship research are also reviewed in the full text. [ABSTRACT FROM AUTHOR]

Majority of the rolling contacts applied in complex interacting machine elements for example bearings and gears perform under Mixed Lubricating (ML) conditions, where the lubricant film can’t fully separate the asperities of the two contacting surfaces. Highly loaded, interacting asperity surrounded with lubricant film, leads to the development of surface originated defects such as scuffing, micropitting, and wear in the ML region. This region exists amid Elastohydrodynamic Lubrication and Boundary Lubrication which needs consolidated knowledge of fluid film and direct contact of asperities, this makes the problem more difficult to solve numerically. Numerous authors have used the Reynolds equation or its modified versions to solve the lubrication problem numerically. However, still, some uncertainty is there to model mixed lubrication operating conditions, with traditional Reynold’s equation, because the assumptions commonly made in Elastohydrodynamic lubrication are not valid within the context of mixed lubrication regime. In this paper previously, used models for mixed lubrication have been examined, and various development in related fields are discussed. Therefore, this review will provide an integrated, synthesized overview of the topic and in turn will lead to benefits for wide-ranging academic, industrial and research communities.

• High cyclic tensile stress is the reason for the RCF damages in LPQ prepared hardened spots. • LPQT can prepare discrete hardened spots surrounded by transitional zone. • The transitional zone helps to alleviate the RCF damages in the hardened spot by decreasing the cyclic tensile stress. • RCF and wear resistances of the LPQT treated rail steel can be balanced by decreasing the transitional zone's thickness. Surface layer with heterogeneous microstructures (SLHM), characterized by hardened spots discretely embedded in a soft substrate, can be prepared by laminar plasma quenching (LPQ) to improve the wear resistance of the railway rail. However, severe rolling contact fatigue (RCF) cracks and spalling would occur in the hardened spots that only consist of quenched microstructure. This study analyzed the RCF damage mechanism of the LPQ prepared hardened spots by contact simulation. To improve the RCF resistance while maintaining the high wear resistance of the treated rail, a novel SLHM, whose discrete hardened spots are surrounded by transitional zone with the hardness lower than that of the quenched zone but higher than that of the substrate, was proposed and prepared by laminar plasma quenching-tempering (LPQT). Then, twin-disc tests and contact simulations were conducted to investigate the wear and RCF resistances of the LPQT treated rail steel. Results showed that the cause of the severe RCF cracks and spalling at the entry side of the LPQ prepared hardened spots was that the cyclic tensile stress at the entry side was always higher than that at the exit side under the cyclic rolling contact loading. The high tensile stress at the entry side of the LPQ prepared hardened spots resulted from the elastic deformation induced by tensile plastic deformation of the neighboring substrate. When the thickness of the transitional zone was about 0.1 mm, the generation of severe RCF cracks and spalling was significantly inhibited in the LPQT prepared hardened spots because the transitional zone decreases the cyclic tensile stress at the entry side of the quenched zone. Besides, the wear loss of such LPQT treated rail steel was only increased by 18.1 % compared with that of the LPQ treated rail steel, indicating that the wear resistance of the LPQT treated rail steel was not significantly reduced. These findings are promising for designing the microstructure of the surface layer to obtain wear-resistant rail with high RCF resistance. [ABSTRACT FROM AUTHOR]

• Increasing turbine rotor sizes have made main bearing reliability a major concern in modern turbines. • Industry and academia have played critical roles in improving the performance and service life of turbine main bearings. • Scholarly contributions have predominantly focused on the fields of bearing geometry and profile optimization. • Tapered roller bearings have received the most research attention compare to spherical roller bearings. • The authors recommend increased exploration of evolutionary bearing geometry optimization techniques. The growing demand for renewable energy has made wind turbines increasingly large and complex. Demand for efficient main bearings optimized to endure dynamic and unpredictable stresses while allowing turbine motion rises even more. Over the years, rolling element bearings have advanced to meet this demand, driven by innovations from industry and academia. This study examined industry-related and academic contributions to the advancement of wind turbine main bearings. Spherical and tapered roller bearings are identified as the basic wind turbine rotor bearings. From the works reviewed, it was found that industry-related contributions on these bearings center on bearing configuration improvements, cage improvements, the development of improved coats, and the design of novel evolutionary variants of the bearings. The SKF was identified as having contributed more to the development of wind turbine rotor bearings with the patenting of two novel bearings: the CARB toroidal bearing and the Nautilus. Scholarly contributions have majored in bearing geometry and profile optimization. Tapered roller bearings were found to have received more research attention than spherical roller bearings. Also, few innovative studies on CARB toroidal bearing, asymmetrical spherical roller bearing, and the Nautilus have been reported. Exclusively theoretical analyses have been mostly used in performance optimizations of the bearings. Only in a few studies did experimental investigations validate theoretical findings, creating potential avenues for experimental studies. Insights from the review indicate that tapered roller bearings or plain bearings could be viable substitute for spherical main shaft bearings, considering their persistent reliability challenges. The authors recommend more exploration of evolutionary bearing optimization techniques, more investigations on bearing lubricants, housing material, cage material, and coating material designs, and increased industry-academic engagement to pave the way for more main bearing innovation. [ABSTRACT FROM AUTHOR]

• Verified frog crack growth model combines impact simulation and fracture analysis. • Crack location and angle are more influential than train speed and axle load. • Observed accelerated growth of transverse cracks near the frog nose. • Proposed inspection strategy based on crack type, cumulative tonnage, and headway. Fatigue cracking is one of the notable failure mechanisms of railway turnout frogs due to high contact forces induced by the wheel-rail impact. However, the treatments specific to the frogs of cast high manganese steel to prevent sudden failure are rarely provided and are independent of the crack conditions, which can significantly affect the fatigue crack growth rate. To address this shortcoming, the fatigue crack growth in a cast high manganese steel frog is computationally investigated with varied wheel and crack conditions. The dynamic wheel-frog impact is first simulated to obtain the distribution of contact pressure imposed on the frog, and the propagation of the fatigue crack is then predicted using the finite element formulation in fracture mechanics. The simulation results show that the train speed and axle load can change the maximum contact stress. Nevertheless, when representing the growth rate in terms of the cumulative passing axle load, the effect of axle load and train speed on the crack growth is minimal and moderate, respectively. In contrast, the initial crack conditions, including the location and angle, have an overweighted influence. As a result, an inspection scheduling strategy for identified cracks with different conditions is proposed to consider both safety and operational efficiency. [ABSTRACT FROM AUTHOR]

• Three dynamic indicators for predicting plastic flow in railway systems based on the mechanics of wheel-rail contact, Tresca's yielding criterion and shakedown theory. • A dynamic method that is simple to model and fast to compute for predicting plastic flow in railway systems. • Key parameters affecting plastic flow and rolling contact fatigue. • A dynamic approach for the impact of plastic flow on rolling contact fatigue damage. • Effect of different degrees of plastic flow on rolling contact fatigue. To analyze the plastic flow of wheels and its impact on rolling contact fatigue (RCF), this article proposes a multibody dynamics approach that is simple to model and fast to compute, based on the mechanics of wheel-rail contact and Tresca yield criterion. This method is used to study the plastic flow of the wheels and is validated by comparing it with plastic flow analysis based on the shakedown theory. The study shows that the dynamics indicators of maximum shear stress, adhesion saturation and stress ratio effectively reflect the plastic deformation of the wheel. Additionally, increasing wheel speed and curve radius, and decreasing wheel-rail friction coefficient, can effectively reduce the area and severity of plastic deformation in the wheel. Ignoring the impact of temperature effects on RCF, it is found that the more severe the plastic flow, the greater the likelihood of RCF. That is, alleviating the plastic flow of the wheel can reduce RCF damage in wheels. This approach to managing the health of wheels provides a comprehensive understanding of the interplay between operational parameters and the mechanical behavior of wheel materials, guiding maintenance strategies and operational decisions to enhance safety and extend the lifespan of railway components. [ABSTRACT FROM AUTHOR]

• The hardness of the soft zone is much lower relative to the hardened surface of the raceway. • A hierarchical finite element modeling method of the main bearing is proposed. • The principle of selecting the optimum hardened depth is given. • The effect of the soft zone on the contact characteristics and fatigue life of the raceway is investigated. • This analyzing method can quickly and efficiently clarify the contact state in the soft zone during the rolling process. A hierarchical finite element modeling method is proposed to study the problem of fatigue spalling easily due to low hardness in the soft zone for the main bearing of a tunnel boring machine. Quasi-static analyses of the main bearing are performed based on the global symmetric model and verified by relative displacement tests of the rings. The invariant contact pressure is replaced by the rolling contact of the rollers in the local sub-model. The contact load is used as an input to solve the stress field, and then the effects of soft zone and hardened depth on the contact characteristics and fatigue lifetime of the sub-model are investigated. The results show there are stress peaks at the junction of the hardened and soft zones. The effect of hardened depth on the stress distribution and fatigue lifetime is relatively small. However, the optimum hardened depth is influenced by the contact load and the permissible stress of the material. The minimum lifetime of the raceway during rolling occurs in the soft zone. This paper achieves a fast and effective rolling contact fatigue analysis of the main bearing, which provides a theoretical basis for optimizing the main bearing design. [ABSTRACT FROM AUTHOR]

10.3390/lubricants11040164 8 Holweger W., Bobbio L., Mo Z., Fliege J., Goerlach B., Simon B. A Validated Computational Study of Lubricants under White Etching Crack Conditions Exposed to Electrical Fields. Lubricants have taken a leading role as drive- train system components in recent years, mainly attributed to their viscosity as a quality criterion. 10.1007/s11426-021-1089-6 4 Holweger W., Bobbio L., Mo Z., Fliege J., Goerlach B., Simon B. A Computational Study on the Role of Lubricants under Boundary Lubrication. [Extracted from the article]

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]

Rolling element bearings typically operate with fluctuating speed, leading to nonstationary vibrations. Moreover, bearings vibration signals are frequently hidden by strong distributions, making it difficult to detect clear bearing fault characteristics for diagnosis. Under this circumstance, the key issue is effectively extracting the transient features from the background interference and highlighting the time-varying fault characteristics. To address this issue, a sparse and low-rank decomposition approach is proposed. In this study, the sparsity of the variable defective characteristics and low-rank of background interference is revealed and exploited for bearing fault detection. Firstly, the time–frequency representation (TFR) of the envelope of measured signal is generated by the time–frequency transform. Then, a sparse and low-rank decomposition model is established based on robust principal component analysis (RPCA) to denoise the measured time–frequency representation and gain the sparse component. Finally, a time–frequency reassignment strategy is utilized to further enhance the capability of detecting the faulty characteristics in the decomposed sparse TFR. The synthetic and actual signals are evaluated to illustrate the reliability and efficacy of the proposed technique. The superiority is also validated by comparisons with STFT, synchrosqueezing transform (SST), ridge extraction method, and scaling-basis chirplet transform (SBCT). • A sparse and low-rank decomposition of time–frequency representation method is proposed for bearing fault diagnosis. • The sparsity of the time-varying fault characteristics and the low-rank property of noise are revealed for the first time. • The strong background interference can be well removed to highlight the fault features. • The effectiveness of the proposed method in simulated signal and actual situation is validated. [ABSTRACT FROM AUTHOR]

Butterfly wings are closely related to the premature failure of rolling element bearings. In this study, butterfly formation is investigated using the developed semi-analytical three-dimensional (3D) contact model incorporating inclusion and material property degradation. The 3D elastic field introduced by inhomogeneous inclusion is solved by using numerical approaches, which include the equivalent inclusion method (EIM) and the conjugate gradient method (CGM). The accumulation of fatigue damage surrounding inclusions is described using continuum damage mechanics. The coupling between the development of the damaged zone and the stress field is considered. The effects of the inclusion properties on the contact status and butterfly formation are discussed in detail. The model provides a potential method for quantifying material defects and fatigue behavior in terms of the deterioration of material properties. [ABSTRACT FROM AUTHOR]

Background: The general counter-roller flow-forming (CRFF) process rarely considers the roller's offset position for the symmetric rollers. However, the rollers' offset position can regulate the tube shape, force, and other features. Studying the novel asymmetric CRFF process, which is the CRFF process with the rollers' offset position, is essential. Methods: The influence of the rollers' offset position, the tube blank thickness, thickness reduction on the material deformation, flow-forming force, final tube middle radius, and thickness in the CRFF process are studied using AA5052 aluminum tube experiments and numerical simulation. Result: The final tubes with three tube blank thicknesses, four thickness reduction, and four rollers' offset positions were obtained by the symmetric and asymmetric CRFF processes. Conclusions: AA5052 aluminum alloy tube can be made by the novel asymmetric CRFF process using a small rollers' offset position (−17.5–0%). Different rollers' positions could change the tube's middle radius. With negative rollers' offset position, the outer roller force is larger than the inner roller force. The force differences increase with the increase of tube blank thickness, the increase of thickness reduction, and the decrease of rollers' offset position. The asymmetric CRFF process helps design and construct large tube flow-forming equipment. [ABSTRACT FROM AUTHOR]

The assembly quality between bearing components will lead to an increase in the load imbalance of each rolling element, which becomes a factor that affects the heat generation of precision bearings. The motion and heat generation of angular contact ball bearing (ACBB) under different assembly states were studied, and the quasi-static model of ACBB with outer ring tilting was established. The contact angle, contact load and motion posture of rolling elements were obtained. Then, the relative imbalance of the outer ring was experimentally simulated based on the outer spacer ring with poor end-parallelism, and the thermal characteristics of the spindle system were monitored. Through theoretical and experimental comparison, the influence of different skew degrees of rings on bearing heat generation and spindle rotation accuracy was discussed. [ABSTRACT FROM AUTHOR]

Wheel wear is one of the most critical factors affecting the vehicle performances and maintenance costs of railway vehicles. However, previous research has to ignore the initial wheel-rail profiles for the evolution of wheel wear. Therefore, this work investigates the relationship between the evolution of wheel wear corresponding to different initial wheel-rail profiles and vehicle dynamics, wheel-rail deterioration. Firstly, the evolution of wheel wear during a long service period is measured from two high-speed railway trains running on two different lines. Contact geometry, e.g., equivalent conicity and contact pair distribution, are extracted. After that, the influence of wheel wear on the vehicle dynamic performance is studied using a multi-body dynamic software. The calculated contact parameters, e.g., pressure, shear traction, and creepage, are used to analyze the distribution of rolling contact fatigue. Based on the experimental and simulation results, the initial wheel and rail profiles significantly affects the wheel wear pattern, the thin rim wheel has uniform wear, and other wheels occurs hollow wear. The hollow wear can lead to gradual deterioration of vehicle dynamics, which conversely aggravates the wheel reprofiling. [ABSTRACT FROM AUTHOR]

Inspired by the surface structure of lotus leaves, micro–nano hierarchical surface structures have been widely used for designing superhydrophobic surfaces. However, the conventionally designed superhydrophobic surface structures are fragile. In this study, a layer of micron-sized mullite whiskers was grown using molten salt on the surface of BaAl 2 Si 2 O 8 (BAS) glass ceramics. Subsquently, SiO 2 nanoparticles modified with 1H,1H,2H,2H-perfluorodecyltriethoxysilane were sprayed onto the whisker layer to form a superhydrophobic surface. The nanoparticles exhibit superhydrophobicity, which is protected by the whisker layer containing pores and bulges. This prohibits direct contact between the nanoparticles and external objects. Contact and rolling angle tests indicated that the surface contact angle of the micro–nano hierarchical structure is 158° and the rolling angle is less than 10°. The stability of the superhydrophobic surface was tested through ultraviolet light, long-time immersion in solutions with various pH values, water scouring, and sandpaper abrasion. The results showed that the contact angle is greater than 150°. This study is expected to provide a simple and effective method for fabricating superhydrophobic surfaces on ceramics on a large scale. [ABSTRACT FROM AUTHOR]

The study of wear that occurs during operation in the wheel–rail assembly is a difficult process to analyze. The phenomena that accompany the wear process are extremely complex and involve many factors, which vary greatly over different periods of time and at different times of wheel–rail contact. Estimating the behavior of the system and its wear in operation is difficult to obtain. However, for common engineering applications, for which the determining factors, such as road profile, load, skid, speed and weather conditions, are known, useful results can be obtained by laboratory tests or by numerical simulation. The article aims to model the complex phenomena that take place in the rail wheel system, taking into account the impact that most essential operational factors have. For this, the Finite Element Method (FEM) is used, thus, trying to explain the wear mechanisms of the wheel–rail system. The obtained results are verified in the laboratory. The main observation in the paper refers to the fact that in the areas of maximum stress and deformation, cracks appear at the micro scale. FEM proved to be a method that can predict the appearance of these microcracks, the experimental results validating the numerical experiments. The research offers results that can prove to be of great importance in practice, for the analysis and improvement of railway safety. [ABSTRACT FROM AUTHOR]

The formation and propagation of cracks in rolling contact fatigue were observed by synchrotron radiation computed laminography, and the effect of stringer‐type inclusion orientation was examined. For longitudinal inclusions, cracks started forming at their tips. After cracks propagated toward the rolling direction, a longitudinal crack was kinked simultaneously at both its tips, and propagated toward the direction perpendicular to the rolling direction to form lateral cracks. After kinking, horizontal cracks were formed from the deepest point of a lateral crack, leading to flaking. On the other hand, for specimens with lateral inclusions, cracks propagated to the lateral direction without the formation of longitudinal cracks. Since the propagation life of lateral cracks and that of horizontal cracks were unrelated to the inclusion orientation, the rolling contact fatigue life of specimens with longitudinal inclusions was considerably longer than that of specimens with lateral inclusions. [ABSTRACT FROM AUTHOR]

A turbo compressor was investigated to ensure the operational reliability of the charging of fuel cell systems. This study investigated air-lubricated herringbone bearings to support the high-speed rotating shaft. For reliable operation of the rotor bearing system, stable operation in the whole speed range (up to 120 krpm), as well as low lift-off speed, is an important issue. Some publications containing guidelines for an optimized design in terms of stability and lift-off behavior date back to the 1970s, with some simplifying assumptions (such as narrow groove theory and small eccentricity analysis). Many publications have addressed the calculations, as well as the optimization of herringbone-grooved bearings; however, general design guidelines are still missing in the view of the authors. Although the investigations related to bearings for the support of a lightweight rotor for a special compressor of a fuel cell unit, this study could also indicate favorable bearing designs for other high-speed applications. Here, the compressible Reynolds equation was solved in the whole solution domain using a conservative finite difference scheme, and the corresponding bearing characteristics were determined. In a perturbation analysis, the linearized dynamic coefficients of the herringbone bearing are calculated. To compare the suitability and performance of the various herringbone-grooved bearing designs, especially at high speed, the simple model of a Jeffcott rotor airborne with two identical herringbone-grooved journal bearings (HGJBs) was used. The geometrical parameters of the HGJBs were varied, and their effects on bearing characteristics and stability were evaluated. Recommendations concerning favorable geometrical bearing parameters for a sufficiently high stability threshold speed and reasonable low lift-off speed were the result of the parameter study. [ABSTRACT FROM AUTHOR]

When a railway vehicle moves on a curved rail, sliding contact between the rail head side and wheel flange causes wear on the wheel flange. Traditionally, a wheel with thinned flange is machined to get a minimum flange thickness specified for structural safety. This operation reduces the rim thickness and shortens the life of the wheel. In the present study, the thinned flanges were hard-faced by submerged arc welding. A welding wire, which has good weldability to the base material of the wheel and does not generate thermal cracking, was developed. The effects of welding polarity on the microstructure, hardness, friction coefficient, and wear characteristics of the welded wheel were studied. The hardness of the wheel welded with reverse polarity was similar to that of welded with straight polarity. The wear rates of the wheel disc welded with reverse polarity and its counterpart rail disc were 11% and 27% lower than those welded with straight polarity. Delamination wear due to subsurface crack propagation and oxidation wear were mixed. The hardness of the rail before the wear test was in the range of 250–300 HV. After the wear test, it soared to 500 HV. [ABSTRACT FROM AUTHOR]

Compared with metal ball bearings, full ceramic ball bearings have more outstanding service performance under extreme working conditions. In order to reveal the lubrication mechanism and improve the operation performance and service life of full ceramic ball bearings, in this paper, the friction, vibration, and temperature rise characteristics of 6208 silicon nitride full ceramic deep groove ball bearing, under the condition of oil lubrication, are studied experimentally. Based on the test results, and through theoretical calculation and simulation analysis, the distribution of the lubricating oil film in bearing contact micro-zone under different working conditions was simulated. After that, the surface of contact micro-zone of full ceramic ball bearing was analyzed. It was found that there is an optimal oil supply for full ceramic ball bearing oil lubrication in service. Under the optimal oil supply lubrication, full film lubrication can be achieved, and the bearing exhibits the best characteristics of friction, vibration, and temperature rise. Compared with the load, the rotational speed of the bearing has a decisive influence on the optimal oil supply. When the rotational speed and load are constant, the minimum oil film thickness and oil film pressure in the contact area of the rolling body decrease with the increase of angle ψ from the minimum stress point of the rolling body. Under the action of high contact stress, thin oil film will be formed in the bearing outer ring raceway. In the field of full ceramic ball bearings, the research content of this paper is innovative. The research results of this paper have an important guiding significance for revealing the oil lubrication mechanism of full ceramic ball bearing and enriching its lubrication theory and methods. [ABSTRACT FROM AUTHOR]

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

The paper considers a rotor system with a nonlinear characteristic. Its equations of motion are a kind of Duffing class equations with multiple degrees of freedom. The paper shows the advantage of using the method of elliptic functions for solving problems of this type. This method enables us to take into account not only vibrations of the rotor installed in elastic nonlinear supports, but also vibrations of the foundation. A comparative analysis of application of the method of elliptic functions proposed by the authors is carried out by comparing the derived equations of motion of the system, as well as by comparing the obtained amplitude-frequency characteristics with the results obtained by the numerical Runge–Kutta–Fehlberg's 4-order method and the approximate analytical Van der Pol method. The regions of resonant frequencies for superharmonic oscillations and bifurcation regimes are determined. It is concluded that the method proposed by the authors is a more accurate and general case than the previously used approximate methods. [ABSTRACT FROM AUTHOR]

In light of the problem of difficult model parameter selection and poor resonance effects in traditional bearing fault detection, this paper proposes a parameter-adaptive stochastic resonance algorithm based on an improved whale optimization algorithm (IWOA), which can effectively detect bearing fault signals of rotating machinery. First, the traditional WOA was improved with respect to initial solution distribution, global search ability and population diversity generalization, effectively improving the global convergence of the WOA. Then, the parameters of the bistable stochastic resonance model were optimized using the improved WOA, and adaptive adjustment of the stochastic resonance parameters was realized. Finally, the Case Western Reserve University bearing data set and the XJTU-SY bearing data set were used as fault data for the actual bearing to be tested for experimental verification. The signal-to-noise ratios of the detected fault frequencies for the above two data sets were −20.5727 and −21.1289, respectively. Among the algorithms compared, the IWOA proposed in this paper had the highest signal-to-noise ratio of the detected fault frequencies. The experimental results show that the proposed method can effectively detect a weak bearing fault signal in enhanced noise. [ABSTRACT FROM AUTHOR]

A train experiences different slip ratios at the wheel/rail contact point as it moves along the rail track, which influences the rolling contact fatigue (RCF) and wear properties of wheel and rail materials. This variation in slip ratios is caused by a change in contact area between the wheel and rail head at curves, as the slip ratio increases compared with when a train is moving on a straight track. When the train is moving on a straight track, the wheel is found to be in contact with the rail head; but that changes when moving around curves, as the wheel flange will now be in contact with the gauge corner of the rail, affecting the severity of wear. Therefore, more research needs to be done to understand the role that slip ratio plays in the wear performance of wheel and rail materials in order to be able to develop models or systems that could be used to predict preventive maintenance. The aim of this work was to investigate the effect of the slip ratio on the wear performance of class B wheels against softer R260 rail steels under rolling and sliding conditions, using a twin-disc setup developed at the University of Pretoria. The results showed that the severity of wear was heavily dependent on the slip ratio - i.e., it increased with the slip ratio, with class B wheels performing better than the softer R260 rail. [ABSTRACT FROM AUTHOR]

In order to study the spatial-temporal distribution characteristics of electromagnetic rail gun temperature, based on moving grid processing method and mod function method, a 3-D geometric model of electromagnetic rail gun under single launch mode, a 2-D geometric model of electromagnetic rail gun under continuous-fire mode, and the corresponding transient electromagnetic field-temperature field coupling model are established by using the finite element analysis software COMSOL Multiphysics, and the temperature spatial-temporal distribution characteristics in the rail-armature contact area, cross section of rail, and along the rail axis is simulated under single launch and continuous launch. The results show that, under the conditions of single launch and natural cooling, the high temperature area in the rail-armature contact surface is located at the rear of the armature due to the skin effect. The temperature distribution along the axial inner side of rail tends to be higher near the tail and lower near the muzzle, it increases with time, but the peak temperature does not exceed the melting point of copper. Under the continuous launch and natural cooling, after five launches, the peak temperature of the rail increases to 709 °C, which is close to the melting point of copper. Continued launching will cause rapid accumulation of heat in the rail and a rapid increase of peak temperature, resulting in shortened life of the launcher and even launch failure. Therefore, without active cooling measures, the electromagnetic rail gun cannot be used in actual combat. The results of the study are an important guide for the design and thermal management of the cooling system of electromagnetic rail gun. [ABSTRACT FROM AUTHOR]

In this study we analyzed the rolling contact fatigue behavior of two types of coatings made by thermal coating, by the method of atmospheric plasma spraying (APS) from two commercially available powders: Ni5Al5Mo and Al2O3 - 13 TiO2. The contact fatigue behavior was studied on an installation specially designed. The specimens were tested for 54 hours (at 1380 rpm), at a load of 944 N. For both types of coatings, the appearance of a wear path was observed, much more obvious in the case of the Ni matrix layer, also confirmed by profilometry. The mechanism of the wear phenomenon was predominantly of plastic deformation type (the material was pushed towards the edges of the wear path) in the case of NiAlMo coating. In the case of ceramic coating, the wear path width was very small (300-450 µm), with very few changes at the surface level of the coating, which recommends this type of material for applications that require wear resistance to rolling. [ABSTRACT FROM AUTHOR]

In this paper, a comparative study of the very‐high‐cycle fatigue (VHCF) behavior of railway wheel steel under axial loading and rolling contact loading was conducted. Fatigue tests were performed with an ultrasonic fatigue test machine under axial loading, and the fracture surfaces from the fatigue tests and shattered rims taken from the failed railway wheels were observed. The wheel steel under axial loading presents a VHCF behavior with Mode I crack, and that under rolling contact loading is a VHCF behavior with mix Mode II–III crack. For the VHCF behavior with Mode I crack, surface and interior crack initiation occurred with equal probability at both low and high stress levels and produced a dual linear S–N curve since the value of fatigue limits for the surface and interior crack initiation are close. For the VHCF behavior with mix Mode II–III crack, cracks were initiated from the interior Al2O3 inclusion, and the fatigue life was beyond 107 cycles. Fatigue bands were observed on the fracture surface under rolling contact loading. The ferrite nanograins formed due to the stress state of shear plastic strain with a large compressive stress. The formed nanograins were softer than the matrix caused by the redistribution of the carbon. Highlight: The VHCF under rolling contact loading is a failure mode of mix Mode II–III crack.The NG massively formed in the VHCF with mix Mode II–III crack.The shear plastic strain with a large compressive stress will help NG formation. [ABSTRACT FROM AUTHOR]

In this study, the behavior of greases during oscillating bearing operation with a small oscillation angle and high frequency was investigated. This mode of operation entails demands on the lubrication system that differ significantly from those for continuously rotating bearings. In order to determine the variables influencing the suitability of a lubricating grease for small angle oscillating operation, the grease samples were examined with particular regard to their rheological properties. The focus of this investigation was to find a relationship between the rheological parameters and the real behavior in the bearing. Therefore, rheological and physical parameters, which influence the long-term structural changes and lubrication conditions, were identified. For this purpose, the viscosity was measured over a wide shear-rate range. The storage and loss modulus, the work of deformation, and the adhesion force jump are also determined. Afterward, rotational transient flow measurements were performed. These allowed us to analyze the development of the shear stress over time, at a constant shear rate, and to examine the internal friction behavior by evaluating the energy density. Subsequently, grease-lubricated four-point bearings were used in component tests, while the frictional torque was measured. These bearings operated in oscillating motion. Moreover, the yield point of mechanically aged greases was measured and compared with that of fresh greases to examine the influence of the oscillating operation on the lubricant condition. Finally, correlations between grease composition, rheological measurements, and component tests were investigated. Thereby, parameters influencing the frictional behavior of greases in rolling bearings during oscillating operation at small swivel angles were identified. [ABSTRACT FROM AUTHOR]

During measurements, the crankshafts of marine engines are usually supported on a set of rigid prisms. Such prisms maintain a constant height position, cause different values of reaction forces and, consequently, may cause elastic deformations of the crankshafts. Thus, the measurements of the dimensions and geometry of the crankshaft may be distorted. This article proposes a measuring system developed to support the crankshaft with a set of flexible supports. These supports implemented the given reaction forces, which ensured the elimination of the crankshaft deformations, regardless of the possible deviations, i.e., in the coaxiality of the main crankshaft journals. The values of these forces were calculated using the finite element method (FEM). These calculations showed that in order to eliminate the crankshaft deformations, the values of the reaction forces must change not only on individual supports, but also with the change of the shaft rotation angle during the measurement. The numerical experiments showed that the application of flexible supports results in uniform contact reaction forces on adjacent main journal supports. This uniformity occurs regardless of the quality of the crankshaft geometry. Thus, the necessity to use a set of flexible supports for measuring marine engine crankshafts was confirmed. The research also showed that the values of the reaction forces ensuring the elimination of shaft deflections under the assumption of nodal support can be treated as corresponding to the resultant reaction forces realized by the prismatic heads. [ABSTRACT FROM AUTHOR]