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The rail profile milling process allows considerable thickness to be removed in a single pass. However, the residual waviness formation law after milling and its subsequent effect on rail performance remains uncertain. In this paper, the wavelength and wave height of the residual waviness are identified as the key characteristics. The relationship between milling speed and residual waviness is determined, and a numerical model of the residual waviness formed on the surface after milling is established based on the commonly used three milling speeds of 300, 600, and 1000 m/h, and its accuracy is verified using the parameters of the residual waviness detected by the milling experiments. A three-dimensional finite element analysis model of wheel-rail contact was employed to analyze the contact stresses and low fatigue cycles at a wheel load of 11.5 tons with no residual waviness on the rail profile surface and with three types of residual waviness, respectively. The results show that the residual waviness changes the wheel-rail contact position and the morphology of the contact area, reduces the maximum contact stress and increases the strain fatigue cycles. The application of elevated milling speeds reduces the wheel-rail contact stresses after milling, thereby increasing the low fatigue cycles. [ABSTRACT FROM AUTHOR]

Fine particle peening (FPP) technology offers an effective method to achieve outstanding surface integrity and fatigue performance in aviation gears. However, the lack of sufficient research on the correlation between process parameters, surface integrity parameters, and fatigue life undermines the full potential of FPP in strengthening aviation gears. Therefore, we have developed an elastic–plastic contact fatigue life model to predict the fatigue life of AISI 9310 gear steel after different strengthening processes. This model can consider surface integrity parameters such as surface micro‐topography, residual stress gradient, and hardness gradient. To validate the model, we conducted rolling contact fatigue tests and compared the results with the predictions from our model. The influence of process parameters on the rolling contact fatigue of AISI 9310 gear steel was further investigated. A process window for FPP was established, and an optimization method was proposed in order to provide guidance for selecting process parameters for FPP on high‐performance aviation gears. HIGHLIGHTS: 1. The rolling contact fatigue life of aviation gear after strengthening is predicted. 2. The simulation results are in good agreement with the rolling contact fatigue tests. 3. A process window for aviation gear steel after FPP is established. [ABSTRACT FROM AUTHOR]

The iron roughneck is an automated piece of equipment utilized for the connection and removal of drilling tools. This paper presents the design of an integrated iron roughneck, providing a detailed introduction to its clamp body structure, along with an analysis of its structural characteristics and performance requirements. The study delves into the integration mode and working characteristics of the clamping mechanism and spin buckle mechanism for the integrated upper clamp body structure of the iron roughneck. Additionally, this paper conducts an in-depth theoretical study on the spin buckle mechanism. Firstly, it analyzes the actual working condition of the spin buckle roller from two perspectives, namely contact theory and rolling friction theory, determining the structural form of the spin buckle roller. Secondly, it investigates the relative displacement between the spin buckle mechanism and the drilling tool, proposing a design method for the floating device mounted on the spin buckle roller and establishing the kinematic equation of the spin buckle roller under the influence of the floating device. Furthermore, the kinematic equations of the spin buckle roller under the influence of the floating device are established. Finally, a dynamics simulation experiment is performed to simulate the working process of the spin buckle mechanism under actual working conditions, analyzing the dynamics and kinematics of the spin buckle mechanism and obtaining the relevant parameter curves of the spin buckle mechanism and drilling tools. Through data comparison and analysis, the correctness of the theoretical analysis results and the rationality of the performance and structure of the spin buckle mechanism are verified. [ABSTRACT FROM AUTHOR]

Rolling element bearings are essential components in modern mechanical equipment, providing crucial support for rotating parts. Hybrid ceramic ball bearings, consisting of steel rings and ceramic balls, have gained popularity in high-speed machinery to enhance performance. These bearings offer advantages such as longer fatigue life, improved performance, and higher speeds. Extensive research by scholars has been conducted to promote the wider adoption of hybrid ceramic ball bearings. This paper compiles relevant studies on hybrid ceramic bearings, organizing literature related to their lifetime, arranging literature pertaining to their performance analysis from the perspective of analytical methods, and collating literature on their lubrication techniques from the angle of lubrication methods. This paper covers research on lifetime modeling, fatigue spalling, wear, mechanical and tribological properties, dynamic performance, thermal analysis, temperature considerations, and lubrication techniques of hybrid ceramic ball bearings. The aim is to provide readers and researchers with a comprehensive overview of these innovative bearings. [ABSTRACT FROM AUTHOR]

As public attention is increasingly drawn toward more sustainable transportation methods, the popularity of electric vehicles (EVs) as part of the solution is rapidly expanding. Operating conditions within EVs can be severe compared to standard combustion powertrains, and the risk of electrical arcing across mechanical surfaces from electric leakage currents incites additional concern. This study employed a series of electro-tribological tests utilizing various moving patterns to improve understanding of the driving conditions for electrically induced bearing damage (EIBD). Rolling ball-on-disk tests were performed with different polyurea-thickened greases. Rotational tests were initially run at various speeds and test durations, but electrical damage was limited. However, electrical damage was unmistakable when a reciprocating motion was used at different track lengths and speeds. These results suggest that the conditions associated with the track length, such as the number of directional changes and speed-dependent film thickness, play a considerable role in forming electrical damage. This work provides critical insights into the mechanisms of EIBD in EVs and other electrical systems. It highlights the importance of understanding the operational conditions that contribute to EIBD, which can lead to improved designs and maintenance practices, ultimately enhancing the efficiency and lifespan of these systems. [ABSTRACT FROM AUTHOR]

Wheel squeal is generally attributed to the lateral wheel vibration induced by lateral creepage. It should be noted, however, longitudinal creepage also exists at wheel/rail interface. Given the significance of longitudinal creepage in vehicle dynamics, a test rig that can introduce various longitudinal creepages by changing the teeth number of synchronous pulley is developed in this research, and measurement results show that squeal spectrum has three dominant peaks, whose sound pressure levels decrease with longitudinal creepage. In order to investigate the reason why longitudinal creepage can mitigate wheel squeal, a model of a wheel/rail system is developed in this research to analyse this phenomenon using complex eigenvalue method, and the results show the inner wheel tends to generate unstable vibration at three different vibration modes, correlating well with the dominant peaks of sound spectrum. Further analyses can illustrate the reason why longitudinal creepage can mitigate wheel squeal: the absolute value of effective damping ratio of each mode decreases with longitudinal creepage, so structural damping and frictional damping are less likely to be overcome by negative damping. [ABSTRACT FROM AUTHOR]

In experiments of aviation motor bearings, when the deep-groove ball bearings are subjected to an overturning moment at high speed, it often happens that the rivet on the cage breaks and the debris invades the raceway, resulting in bearing failure. To address the problem of early failure of deep-groove ball bearing cages and rivets in aviation motors, the causes of early failure were analyzed from the aspect of cage design in this study. The influence of the raceway and cage structure parameters on the dynamic contact characteristics of the rolling element and cage under the action of overturning torque were analyzed, the weak link of the cage was determined, and the cage design parameters were optimized. The results show that with an increase in the cage width and pocket radius, the impact force between the ball and cage first decreases and then increases, and the tilt angle of the cage gradually decreases. A larger channel radius and smaller clearance can slow down the interaction between the cage and the rolling element and make the cage run more smoothly. Increasing the thickness of the cage can ensure that the rivet part of the cage is at a low stress level, and the risk of premature fatigue failure at the rivet part can be reduced by maintaining a small gap–fit relationship between the rivet and rivet holes. The research results indicate that the working condition adaptability of the bearing cage for aviation motors can be improved, and the design method for this type of bearing can be enhanced. [ABSTRACT FROM AUTHOR]

This paper addresses the issue of the frequent collision and grinding of rolling elements in cageless bearings during operation by proposing a method to calculate the total circumferential clearance. The calculation is based on the maximum orbital speed difference in the bearing rolling elements to determine the minimum clearance needed to prevent collision. The study analyzes the impact of the rolling element diameter, bearing pitch diameter, contact angle, and number of rolling elements on the total circumferential clearance. The discussion then focuses on optimizing the number of rolling elements in cageless bearings. The optimization results demonstrate that the proposed calculation reduces collisions between rolling elements and bearing stress. Additionally, a total circumferential clearance test was conducted on a logarithmic spiral bearing, showing significant improvements in wear, average temperature, and temperature rise when designed according to the method presented in this article. These findings offer valuable insights into the design of cageless bearings. [ABSTRACT FROM AUTHOR]

Based on the cohesive zone model (CZM), a finite element model of the film–substrate bearing system in the rolling–sliding contact state is established. Through analyzing the normal and tangential bearing states of the film–substrate system, the effects of the sliding–rolling ratio and the film–substrate adhesion strength on the interfacial stress and the interfacial energy release rate of the film–substrate system are studied. The results show that there is an almost symmetric stress distribution at both sides of the contact zone in rolling contact. In rolling–sliding contact, obvious shear flow along the rolling–sliding direction occurs at the front edge of the contact zone, which results in a significant increase in the shear stress at the interface at the front edge of the contact zone, increasing the risk of interface damage and delamination failure. Meanwhile, the shear flow causes a normal tensile stress concentration along the film surface behind the contact zone, which very easily causes the emergence and expansion of the film surface cracks. In addition, there is a clear positive correlation between the adhesion strength and the load-bearing capacity of the film–substrate interface. The tangential delamination damage mainly occurs at the interface regardless of the rolling or rolling–sliding contact state. [ABSTRACT FROM AUTHOR]

Squeeze film dampers are used to reduce vibration in aircraft jet engines supported by rolling element bearings. The underlying physics of the squeeze film dampers has been studied extensively over the past 50 years. However, the research on the SFDs is still ongoing due to the complexity of modeling of several effects such as fluid inertia and the modeling of the piston rings, which are often used to seal SFDs. In this work, a special experimental setup has been designed to validate the numerical models of SFDs. This experimental setup can be used with various SFD geometries (including piston ring seals) and simulate almost all conditions that may occur in an aircraft jet engine. This work also focuses on the inertia forces of the fluid. The hydrodynamic pressure distribution of a detailed 3D-CFD model is compared with the solution of the Reynolds equation including inertia effects. Finally, the simulation results are compared with experimental data and good agreement is observed. [ABSTRACT FROM AUTHOR]

Bogie hunting instability is one of the common faults in railway vehicles. It not only affects ride comfort but also threatens operational safety. Due to the lower operating speed of metro vehicles, their bogie hunting stability is often overlooked. However, as wheel tread wear increases, metro vehicles with high conicity wheel–rail contact can also experience bogie hunting instability. In order to enhance the operational safety of metro vehicles, this paper conducts field tests and simulation calculations to study the bogie hunting instability behavior of metro vehicles and proposes corresponding solutions from the perspective of wheel–rail contact relationships. Acceleration and displacement sensors are installed on metro vehicles to collect data, which are processed in real time in 2 s intervals. The lateral acceleration of the frame is analyzed to determine if bogie hunting instability has occurred. Based on calculated safety indicators, it is determined whether deceleration is necessary to ensure the safety of vehicle operation. For metro vehicles in the later stages of wheel wear (after 300,000 km), the stability of their bogies should be monitored in real time. To improve the stability of metro vehicle bogies while ensuring the longevity of wheelsets, metro vehicle wheel treads should be reprofiled regularly, with a recommended reprofiling interval of 350,000 km. [ABSTRACT FROM AUTHOR]

The cable saddle structure is the main support component for long-span bridges to transmit cable force, which is of great significance for the structural force system. Nowadays, the main cable saddle structures used in long-span bridges are mainly traditional anti-slip saddles and innovative rolling saddles. To clarify the characteristics of the saddles in long-span bridges, the design principles, mechanical properties, and casting process of these two types of saddle structures were researched. A rolling saddle in a bridge project was taken as an example and its mechanical situation in the roller area was investigated. The results showed that the stress concentration phenomenon is prone to occurring in the rolling saddle because of the line contact in the contact area and the rolling saddle is mainly subjected to vertical force. Thus, attention should be paid to the von Mises stress in the contact area between the saddle base and the roller shaft, the lower surfaces of both ends of the roller shaft, and the top surface of the tower, to avoid material damage. Furthermore, the casting process of the anti-slip saddle structure is mature, but also faced with problems due to the welding of thick plates, and urgently needs to be improved and upgraded. The rolling saddle is used with the all-welded casting process, but its technology is relatively immature and the requirements for the roller shaft material performance are strict. The research results can provide a reference for the selection and design of the saddle structure in long-span bridges. [ABSTRACT FROM AUTHOR]

A simple dynamic system with dry friction is studied theoretically and numerically. Models of systems including dry friction are not easily obtained, as defining the relationship between the friction force and the relative velocity presents a significant challenge. It is known that friction forces exhibit notable discontinuities when there is a change in the direction of motion. Additionally, when the relative motion ceases, the friction force can assume any value within a certain range. In the literature, numerous models of dry friction are presented, and most of them assume a biunivocal dependency of the friction force with respect to relative velocity. The dynamic system considered here is a tilted rod with spherical ends, initially at rest. Dry friction forces are evident at the contact point with the horizontal plane. The ball–plane contact highlights the rolling friction or/and sliding friction. The problem is theoretically solved after adopting one of the two cases of friction: rolling friction or sliding friction. The nonlinear differential equations of motion have been derived, along with expressions for the magnitude of the normal reaction and the friction force. The results of the model are displayed graphically for three different sets of values for the coefficient of friction. It is revealed that there is a critical value of the coefficient of friction that determines the transition from rolling to sliding regimes. To validate the theoretical model, dynamic simulation software was utilised. The excellent match between the theoretical predictions and the results from the numerical simulation confirms the accuracy of the proposed analytical solution. [ABSTRACT FROM AUTHOR]

An express method for assessing the effectiveness of lubricating compositions with nano-additives of various chemical compositions is proposed, and a joint analysis of experimental data on the changes in the value of wear and the level of damage to the surface layers of metallic friction pairs was performed. The variation in the current relative hardness of the sample's surface, the variation in the current relative material damage level, the current value of wear, and the current level of the coefficient of friction were chosen as the key parameters to conduct a performance assessment. The level of material damage in the contact zone was determined using the parameters of the statistical law of hardness value scattering. Based on an analysis of data in the literature, it was observed that the structural changes occurring in metallic materials during long-term, cyclic, static, and frictional loading are correlated with changes in the statistical characteristics of the hardness scattering results. An experimental substantiation of the proposed method was carried out for steel-sliding friction pairs using lubricating compositions based on Greaseline Lithium BIO Rail 000 oil manufactured by AIMOL with nano-additives of copper, magnesium and aluminum alloys, graphite, and two grades of medium-carbon steel. According to the system of indicators presented in this research, the greatest efficiency (in terms of increasing the wear resistance of friction steel pairs) was achieved with lubricating compositions including nano-powder additives made of steel, which have lower hardness. For the friction experiments, where the determining factor was abrasive wear, such lubricants ensured minimal damage and wear to the friction surface, while the value of the friction coefficient was maintained at a level that is optimal for wheel–rail friction pairs. [ABSTRACT FROM AUTHOR]

This article presents a vibration model of neighboring rolling parts that takes into account non-smooth symmetric collisions. This model was used to examine the motion state of the rolling element and the collision force between nearby rolling elements. It also determined the motion posture and overall collision form of the rolling element after setting the functional slot. Afterwards, the level of disorderly movement and the structure of the moving object were examined and confirmed through the use of a phase diagram of the motion system in relation to zero symmetry, the Lyapunov exponent, and a platform for measuring irregular vibrations in the bearing. This work aims to clarify the factors that contribute to the persistent chaotic state of rolling elements in bearing vibration. [ABSTRACT FROM AUTHOR]

In the analysis of tribological contacts, the focus is often on a singular question or result. However, this entails the potential risk that the overall picture and the relationships could be oversimplified or even that wrong conclusions could be drawn. In this article, a comprehensive consideration of test results including component and lubricant analyses is demonstrated by using the example of rolling contact. For this purpose, thrust cylindrical roller bearings of type 81212 with unadditized base oils were tested in the mixed-friction area. Our study shows that by using an adapted and innovative surface analysis, a deeper dive into the tribo-film is feasible even without highly sophisticated analytical equipment. The characterization of the layers was performed by the three less time-consuming spatially resolved analysis methods of µXRF, ATR FTIR microscopy and Raman spectroscopy adapted by Schaeffler. This represents a bridge between industry and research. The investigations show that especially undocumented and uncontrolled contamination of the test equipment could lead to surprising findings, which would result in the wrong conclusions. Simple substances, like hydrocarbons, are demanding test specimens. [ABSTRACT FROM AUTHOR]

Due to the long-term service through wheel-rail rolling contact, the train wheelset tread will inevitably suffer from different types of defects, such as wear, cracks, and scratches. The effective detection of wheelset tread defects can provide critical support for the operation and maintenance of trains. In this paper, a new method based on a local inference constraint network is proposed to detect wheelset tread defects, and the main purpose is to address the issue of insufficient feature spaces caused by small samples. First, a generative adversarial network is applied to generate diverse samples with semantic consistency. An attention mechanism module is introduced into the feature extraction network to increase the importance of defect features. Then, the residual spine network for local input decisions is constructed to establish an association between sample features and defect types. Furthermore, the network's activation function is improved to obtain higher learning speed and accuracy with fewer parameters. Finally, the validity and feasibility of the proposed method are verified using experimental data. [ABSTRACT FROM AUTHOR]

In this study, to investigate the problem of contact fatigue and the damage mechanism of an AD180 high-carbon semi-steel roll, rolling contact fatigue tests were conducted using specimens cut from the periphery of a roll ring. These specimens were characterized under different contact stresses using SEM, a profile system, an optical microscope, and a Vickers hardness tester. The results indicates that the main forms of fatigue damage of an AD180 high-carbon semi-steel roll are peeling, pitting corrosion, and plowing. Moreover, the surface of the roll exhibits delamination and plastic deformation characteristics under high contact stress. Meanwhile, the size and depth of peeling, as well as the amount of pitting corrosion, increase with the contact stress. Peeling is mainly caused by a crack that originates at the edge of the specimen surface and propagates along the pearlite structure and the interface between pearlite and cementite. High contact stress can lead to an increase in the crack propagation depth and angle, resulting in the formation of larger peeling. Under cyclic loading, the near-surface microstructure of the specimen hardens due to grain refinement and dislocation strengthening, and the depth of the hardened layer increases with the increase in contact stress. When the contact stress reaches 1400 MPa, the near surface structure of the specimen changes from pearlite to troostite. [ABSTRACT FROM AUTHOR]

The azimuth track is an important component of the radio telescope wheel–rail system. During operation, the azimuth track is inevitably subject to phenomena such as track wear, track fatigue cracks, and impact damage to welded joints, which can affect observation accuracy. The 110 m QiTai radio telescope (QTT) studied in this paper is the world's largest fully steerable radio telescope at present, and its track will bear the largest load ever. Since the welded joint of an azimuth track is the weakest part, an innovative welding method (multi-layer and multi-pass weld) is adopted for the thick welding section. Therefore, it is necessary to study the contact mechanical properties between the wheel and the azimuth track in this welded joint. In this study, tensile tests based on digital image correlation technology (DIC) and Vickers hardness tests are carried out in the metal zone (BM), heat-affected zone (HAZ), modified layer, and weld zone (WZ) of the welded joint, and the measured data are used to fit the elastic–plastic constitutive model for the different zones of the welded joint in the azimuth track. Based on the constitutive model established, a nonlinear finite element model is built and used to simulate the rolling mechanical performance between the wheel and azimuth track. Through the analysis of simulated data, we obtained the stress distribution of the track under different pre-designed loads and identified the locations most susceptible to damage during ordinary working conditions, braking conditions, and start-up conditions. The result can provide a significant theoretical basis for future research and for the monitoring of large track damage. [ABSTRACT FROM AUTHOR]

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

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

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

In the continuous casting process, the rolling die is exposed to non-steady stress conditions that can initiate thermo-mechanical fatigue damage. Understanding the rolling die failure mechanism is essential in metal-forming industries. Thermo-mechanical fatigue damage mechanism (crack growth) is governed by highly localized stresses in the crack tip region. This paper presents analytical models to determine thermo-mechanical fatigue failure mechanism based on the elastoplastic fracture mechanics and continuum damage mechanics. The model includes new proposed analytical equations for low-cyclic fatigue crack propagation. To verify the analytical models, experimental data and finite element simulation are considered. Results show good agreement with experimental data and finite element simulation.

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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