Rolling Contact Fatigue Damage Research Articles

Gearless Track-Friendly Metro with Guided Independently Rotating Wheels

Track–vehicle severe interaction on track with small curve radius results in rail wear and corrugation, and wheel polygonization, which drain considerable resources for rail grinding and wheels re-profiling in metro lines. To reduce the damage caused by track-vehicle severe interaction, the paper analyzes the reasons leading to rail wear and then proposes an architecture of a metro vehicle with independently rotating wheels driven directly by permanent magnet synchronous motors. The architecture is axle guidance, offered by passive linkages, which ensures that all axles are oriented radially, while control strategy was kept as simple as possible, identifying only two basic traction conditions. The concept is first discussed and then validated through a comprehensive set of running dynamics simulation performed with a multibody software to evaluate rail wear and rolling contact fatigue in traction/braking, coasting with different cant deficiency/excess conditions. The multibody dynamics simulation shows that the proposed architecture is virtually capable of avoiding both wear and rolling contact fatigue damages, and achieves the highest possible track friendliness. The concept of the proposed architecture is a track-fiendly metro architecture and could be a good reference for reducing rail-track interaction damages and maintainace cost.

Fatigue life analysis of wheel-rail contacts at railway turnouts using finite element modelling approach.

The article deals with wheel-rail contact analysis at railway turnout using a finite element modelling approach. The focus is understanding the wheel-rail contact problems and finding the means of reducing these problems at railway turnouts. The main aim of the work reported in this article is to analyse fatigue life and simulate the wheel-rail contact problems for a repeated wheel loading cycle by considering the effect of normal and tangential contact force impact under different vehicle loading conditions. The study investigates the impact of tangential contact force generated due to different-angled shapes of the turnout and aims to reveal how it affects the life of contacting surfaces. The obtained results show that the maximum von-Mises equivalent alternating stress, maximal fatigue sensitivity, and maximum hysteresis loop stresses were observed under tangential contact force. These maximum stresses and hysteresis loops are responsible for rolling contact fatigue damage, and excessive deformation of the wheel-rail contact surface. At a constant rotational velocity, the tangential contact force has a significant impact on the fatigue life cycle and wheel-rail material subjected to fatigue damage at lower cycles compared to the normal contact force. The finite element modelling analysis result indicated that the contact damages and structural integrity of the wheel-rail contact surface are highly dependent on contact force type and can be affected by the track geometry parameters.

Rail RCF damage quantification and comparison for different damage models

There are several fatigue-based approaches that estimate the evolution of rolling contact fatigue (RCF) on rails over time and built to be used in tandem with multi-body simulations of vehicle dynamics. However, most of the models are not directly comparable with each other since they are based on different physical models even though they shall predict the same RCF damage at the end. This article studies different approaches to quantifying RCF and puts forward a measure for the degree of agreement between them. The methodological framework studies various steps in the RCF quantification procedure within the context of one another, identifies the ‘primary quantification step’ in each approach and compares results of the fatigue analyses. In addition to this, two quantities—‘similarity’ and ‘correlation’—have been put forward to give an indication of mutual agreement between models. Four widely used surface-based and sub-surface-based fatigue quantification approaches with varying complexities have been studied. Different operational cases corresponding to a metro vehicle operation in Austria have been considered for this study. Results showed that the best possible quantity to compare is the normalized damage increment per loading cycle coming from different approaches. Amongst the methods studied, approaches that included the load distribution step on the contact patch showed higher similarity and correlation in their results. While the different approaches might qualitatively agree on whether contact cases are ‘damaging’ due to RCF, they might not quantitatively correlate with the trends observed for damage increment values.

Novel S-N curve for different hardened layers in point and line contact

Rolling contact fatigue (RCF) regularly causes mechanical components to fail under cyclic loads. Popular surface treatment processes such as case hardening (carburization), nitriding and tempered martensitic reduce the effect of RCF damage. This paper presents multi-stage S-N curve for steels with different surface treatments, under point and line contact conditions using RCF tribometers for the experiments and finite element (FEM) simulation to simulate localised stresses in the contacts. Additionally, S-N tests with 0, 5 and 11% slide to roll ratio (SRR) are presented. This work demonstrates the importance of testing key points at RCF S-N curves to optimize the hardened layers.

Effects of solid friction modifier on friction and rolling contact fatigue damage of wheel-rail surfaces

In railway network, friction is an important factor to consider in terms of the service behaviors of wheel-rail system. The objective of this study was to investigate the effect of a solid friction modifier (FM) in a railway environment. This was achieved by studying the friction, wear, and rolling contact fatigue (RCF) damage on the wheel-rail materials at different slip ratios. The results showed that when a solid FM was applied, the friction coefficient decreased. After the solid FM was separated from the wheel-rail interface, the friction coefficient gradually increased to its original level. With the application of the solid FM, the wear rates of the wheel-rail decreased. In addition, the thickness and hardness of the plastic deformation layers of the wheel-rail materials were reduced. The worn surfaces of the wheel-rail were dominated by pits and RCF cracks. Without the FM, RCF cracks ranged from 84 to 120 µm, and subsurface cracks were generated. However, with the FM, RCF cracks ranged from 17 to 97 µm and no subsurface cracks were generated. These findings indicate possible methods of improving the performance of railway rolling stock by managing friction, and reducing wear and permanent RCF damage affecting both the wheels and rails.

Physics-based data-driven interpretation and prediction of rolling contact fatigue damage on high-speed train wheels

Rolling contact fatigue (RCF) of high-speed train wheels is detrimental to reliability and entails huge maintenance costs. Accurate prediction of RCF damage is important for train operators, however, physics-based methods are not suitable for practical applications. Based on accumulated RCF data, this paper develops a physics-based data-driven method for the interpretation and prediction of RCF damage risk. First, based on RCF mechanism, it is found that many relevant parameters can be used for RCF prediction. Then, eight predictors are extracted from RCF-related data through dimensionality reduction methods, including linear discriminant analysis and kernel Fisher discriminant analysis. It shows that greater wheel out-of-roundness or smaller wheel diameters leads to higher RCF risks; previously defective wheels are more likely to reencounter RCF damage; the RCF risk varies in different seasons; the effect of wear on RCF damage is significantly nonlinear. Afterwards, a predictive model is established based on logistic regression. Validation results yield an average accuracy of 75% and also demonstrate its easy interpretability, fast computational speed and stable performance. Further, test result shows an accuracy of 85% to distinguish high-risk wheelsets prior to RCF inspections. The proposed method can be applied to the risk-based maintenance of high-speed train wheels.

Railway wheel tread damage and axle bending stress – Instrumented wheelset measurements and numerical simulations

ABSTRACT A combination of instrumented wheelset measurements and numerical simulations of axle bending stresses is used to investigate the consequences of evolving rolling contact fatigue (RCF) damage on a passenger train wheelset. In a field test campaign, stresses have been monitored using a wheelset with four strain gauges mounted on the axle, while the evolution of wheel tread damage (out-of-roundness) has been measured on regular occasions. The strain signals are post-processed in real time and stress variations are computed. Based on a convolution integral approach, the measured wheel out-of-roundness has been used as input to numerical simulations of vertical dynamic wheelset–track interaction and axle stresses. Simulated and measured axle stresses are compared for cases involving combinations of low or high levels of rail roughness and the measured levels of RCF damage. The study enhances the understanding of how wheel tread damage and track quality influence axle stress amplitudes.

Comparison of rolling contact fatigue damage between railway wheels and twin-disc test specimens

Management of wheel-rail contact is of great importance for railways. It is essential to understand the tribology of railway materials to maximize productivity and reduce maintenance. Many studies on wear and rolling contact fatigue (RCF) were performed, ranging from field and full-scale experiments to small-scale tests, such as twin-disc. However, comparison between results found in these distinct approaches are few. Thus, RCF damage was compared between twin-disc specimens and wheels removed from field operation. Some aspects of RCF were remarkably similar, such as plastically deformed layer thickness, microhardness, crack angle and material delamination. However, cracks depth and length were 10–15 times larger in wheels. Finally, laboratory tests hardly simulate RCF in advanced stages and relevant environmental effects.

Effects of dent size on the evolution process of rolling contact fatigue damage on defective rail

Defects such as dents on the rail surface might induce severe rolling contact fatigue (RCF) and then threaten the running safety of railway vehicles. This study aims to explore the initiation and propagation of RCF cracks around dents with different sizes through observing both surfaces and cross-sections of the defective rail. The experiments are conducted on a wheel/rail twin-disc machine. Results indicate that the microstructure evolution process around the dent can be divided into three main stages, namely crack initiation, crack propagation and dent removal. Dents in different sizes act very similarly in each stage, including the position, the crack growth path and the final appearance after the dent has been fully worn off. However, dents in different sizes cause different lifetimes of crack initiation and different lasting times of dents at each stage. For the lager dent, cracks initiate later but propagate for a longer time period, so the dent size plays an important role in the RCF evolution process.

Experimental study on the wear and damage of wheel-rail steels under alternating temperature conditions

The objective of this study is to investigate the wear and rolling contact fatigue (RCF) damage of wheel and rail materials under alternating temperature conditions. Two series of rolling-sliding tests were performed: (1) at 20 °C for 75,000 cycles, and then continued at −40 °C for 10,000, 30,000, and 75,000 cycles, respectively; (2) at −40 °C for 75,000 cycles, and then continued at 20 °C for 10,000, 30,000, and 75,000 cycles, respectively. The results indicated that the decrease in the temperature would alleviate the wheel wear due to the formation of wear debris layer. Both the rising and dropping of the environmental temperature during the tests could lead to the increase in the rail wear. Besides, the decrease in the temperature could increase the plastic deformation and work hardening of wheel and rail discs. In addition, the crack initiation was correlated with the behaviour of plastic flow on the wheel. At 20 °C, long single cracks initiated and propagated along the highly deformed ferrite boundaries. At −40 °C, white-etching layer (WEL) was observed only on the wheel surface, which was mainly attributed to the severe plastic deformation. Then, the refined ferrites and WELs were the main crack initiation sources on the wheel.

An interdisciplinary framework to predict premature roller element bearing failures in wind turbine gearboxes

Roller element bearings present in the intermediate and high-speed stages of wind turbine gearboxes operate in dynamic working conditions and in some cases may fail within 30% or less of their designed lifetime. Upon investigation, it has been identified that these premature failures happen due to a peculiar failure mode associated with formation of white etching cracks (WEC). This continues to be a great challenge for the wind energy operators as it leads to an increase of maintenance and operation costs in addition to long wind turbine downtime. Therefore, the industry is in dire need of a lifetime prediction methodology that could take in multi-scale inputs ranging from bearing loads at the system level down to the level of bearing material properties at the microscopic level. This work summarizes the overall approach of a project that aims towards an integrated framework which links load data from the bearings and microstructure related non-metallic inclusion statistics from bearing steels, to predict a material based probability of failure. The interlink between both aspects is a numerical rolling contact fatigue (RCF) framework based on finite element analysis, which includes multi-scale data as an input to calculate rolling contact fatigue damage. The outcome will help the wind industry to better predict bearing failures.

Adhesion and damage characteristics of wheel/rail using different mineral particles as adhesion enhancers

Mineral particles are used to improve adhesion between wheel and rail, but they might lead to severe damages of wheel and rail surfaces. To investigate the adhesion enhancement phenomena and damages of both wheel and rail induced by adhesion enhancers, the crushing strengths of four types of mineral particles (zinc oxide, sand, spinel and alumina) were firstly explored on a uniaxial compression tester. Then the adhesion, wear and damage of wheel/rail were studied on a twin-disc machine under the wet condition. The results show that the characteristic crushing strength was 24 MPa for zinc oxide, 40 MPa for sand, 51 MPa for spinel and 73 MPa for alumina, respectively. For particle with the lowest crushing strength (zinc oxide), the adhesion coefficient was the lowest (around 0.20). With the increase in the crushing strength to 40 MPa, the adhesion coefficient was improved to around 0.28. The particles with higher crushing strengths induced larger wheel/rail wear rates and severer rolling contact fatigue (RCF) damages on wheel and rail. The RCF cracks were large in lengths but small in angles, which finally developed into large pieces of material peeling off from the surface. Sand was the most suitable adhesion enhancer considering its good adhesion enhancement and the relatively mild damage on wheel/rail materials.

Rolling contact fatigue deformation mechanisms of nickel-rich nickel-titanium-hafnium alloys

The deformation mechanisms that dictate the tribological performances of heat treated Ni55Ti45, Ni54Ti45Hf1 and Ni56Ti36Hf8 alloys are revealed through rolling contact fatigue (RCF) testing and transmission electron microscopy (TEM) analyses. Analysis of worn samples that passed a 5×108 cycle RCF runout condition shows that damage is primarily confined to deformation bands that propagate several hundred nanometers – to – several microns beneath the surface. These bands nucleate via localization of dislocation slip within the B2 austenite phase of the alloys. For the Ni55Ti45 and Ni54Ti45Hf1 samples, further damage and eventual spall failures occur by shearing and dissolution of the strengthening Ni4Ti3 nanoprecipitates within the deformation bands, followed by nanocrystallization that sometimes includes stress-induced nucleation of B19′ nanocrystals. Eventually, complete amorphization occurs prior to fracture. The relative 15 – 25% increase in RCF contact stress performance of the Ni56Ti36Hf8 alloy correlates with a more limited depth of damaged material beneath the wear surface; heavily damaged material beneath spall failure sites only extends 1.5 µm into the sample, compared to > 6 µm for Ni55Ti45 and Ni54Ti45Hf1 alloys. This superior RCF damage resistance of the Ni56Ti36Hf8 alloy results from a lower fraction of B2 matrix phase (≤ 13 %) that is highly confined by both cubic Ni-rich NiTiHf and H-phase nanoprecipitates. Specifically, this microstructure limits the widths of deformation bands within the B2 austenite phase to less than the size of the strengthening nanoprecipitates, which in turn inhibits precipitate shearing and dissolution processes that precede nanocrystallization and amorphization.

Monitoring the Damage Evolution in Rolling Contact Fatigue Tests Using Machine Learning and Vibrations

This study shows the application of a system to monitor the state of damage of railway wheel steel specimens during rolling contact fatigue tests. This system can make continuous measurements with an evaluation of damage without stopping the tests and without destructive measurements. Four tests were carried out to train the system by recording torque and vibration data. Both statistical and spectral features were extracted from the sensors signals. A Principal Component Analysis (PCA) was performed to reduce the volume of the initial dataset; then, the data were classified with the k-means algorithm. The results were then converted into probabilities curves. Metallurgical investigations (optical micrographs, wear curves) and hardness tests were carried out to assess the trends of machine learning analysis. The training tests were used to train the proposed algorithm. Three validation tests were performed by using the real-time results of the k-means algorithm as a stop condition. Metallurgical analysis was performed also in this case. The validation tests follow the results of the training test and metallurgical analysis confirms the damage found with the machine learning analysis: when the membership probability of the cluster corresponding to the damage state reaches a value higher than 0.5, the metallurgical analysis clearly shows the cracks on the surface of the specimen due to the rolling contact fatigue (RCF) damage mechanism. These preliminary results are positive, even if reproduced on a limited set of specimens. This approach could be integrated in rolling contact fatigue tests to provide additional information on damage progression.

Effects of Molybdenum Addition on Rolling Contact Fatigue of Locomotive Wheels under Rolling-Sliding Condition.

Rolling contact fatigue (RCF) damages often occur, sometimes even leading to shelling on locomotive wheel treads. In this work, the RCF damage behaviors of two locomotive wheel materials with different molybdenum (Mo) contents were studied, and the influence of depth of wheel material was explored as well. The result indicates that with the increase in the Mo content from 0.01 wt.% (wheel 1, i.e., a standard wheel) to 0.04 wt.% (wheel 2, i.e., an improved wheel), the proeutectoid ferrite content and the interlamellar spacing of pearlite decreased, the depth and length of the RCF cracks increased and the average RCF live of locomotive wheel steel improved by 34.06%. With the increase in the depth of material, the proeutectoid ferrite content and the interlamellar spacing of pearlite increased, the depth of RCF cracks increased, the length of RCF cracks of wheel 1 increased and then decreased whereas that of wheel 2 decreased, the RCF live showed a decrease trend for wheel 1, while the RCF life increased and then decreased for wheel 2. The processes of shelling can be divided into three patterns: cracks propagating back to the surface, crack connection and fragments of surface materials.

Comparison of wear and rolling contact fatigue behaviours of bainitic and pearlitic rails under various rolling-sliding conditions

Rolling-sliding wear experiments were performed to investigate the wear and rolling contact fatigue (RCF) behaviours of a premium pearlitic rail (PH), a carbon-free bainitic rail (BH) and two standard pearlitic rails (U71Mn and U75V). The wear regime and RCF damage evolution of the PH and BH materials in terms of Tγ/A (i.e. creepages and contact pressures) were compared and analyzed. The high-hardness BH steel presented a wear resistance similar to U71Mn and U75V rail materials, whereas lower wear rate was shown by the PH steel. Concerning the RCF performance, the damage of BH steel (comparable to U75V) was more severe than that of PH steel (comparable to U71Mn). Finally, with the increase in creepages and pressures, the wear and RCF damage of both PH and BH steels increased. These information could provide a guide in choosing rail materials and in development of bainitic rails.

Comparison on the wear properties and rolling contact fatigue damage behaviors of rails by laser cladding and laser-induction hybrid cladding

In this paper, the wear properties and rolling contact fatigue (RCF) damage behaviors of the rails with Ni-based coatings deposited by laser cladding (LC) and laser-induction hybrid cladding (LIHC) are studied comparatively by roll–sliding contact tests. The results indicate that the RCF damage characteristics of the rail rollers by both LC and LIHC are almost same at the maximum contact stress σmax ≤ 800 MPa, while the wear rate of rail roller by LC is slightly lower. However, when the maximum contact stress increases to σmax ≥ 1230 MPa, the coatings and heating affected zone (HAZ) at the contact edge of the rail roller by LC spall and fracture severely, leading to much higher wear rate and much poorer smoothness than that by LIHC. Thus, compared with LC technology, LIHC technology can reduce the wear rate and contact fatigue damage extent of rails at higher contact stress, and thereby maintain the surface profile and smoothness better.

Geospatial and temporal data mining to combine railway low adhesion and rail defect data

Rolling contact fatigue (RCF) damage to rails and low adhesion at the rail–wheel interface remain significant problems in maintaining railway performance, fully utilising network capacity and reducing running costs. A novel approach has been developed to understand these problems through analysis of data on RCF and low-adhesion incidents from the UK rail network. This augments understanding of specific mechanisms such as the roles of rail plasticity in crack initiation and environmental moisture levels in low adhesion, which have not given sufficient information to prevent these problems to date. A moving-window filtering technique and temporal and geospatial approaches were used to identify correlations between sites of low rail–wheel adhesion subject to transient sliding contact, crack initiation and underbridge locations where vertical and lateral track stiffness typically change rapidly. The analysis showed that a high density of otherwise unexpected RCF defects occurred close to underbridges and that there was a strong correlation between momentary slides during braking and RCF sites. The temporal analysis indicated that, although concentrated in the autumn period, 55–60% of transient low-adhesion incidents occur outside that period, with the highest risk in the very early morning.

Effects of axle load transfer on wheel rolling contact fatigue of high-power AC locomotives with oblique traction rods

Severe wheel rolling contact fatigue (RCF) has been observed on two types of high-power AC locomotives with CO-CO axle arrangement and running in complicated environments in China. This RCF occurs as continuous lateral surface cracks in the zone approximately centered at the nominal rolling circle of wheels and can propagate downward up to 14.5 mm deep. To figure out the causes, field observations, monitoring tests and numerical simulations have been conducted in the past years together with systematic comparisons between two types of locomotives. Statistics have shown an interesting phenomenon, among others, that wheels on axles 3 and 4 are most susceptible to RCF cracks on Type B locomotives, but not so on Type A. It has been found that complicated running environments such as sharp curves and large slopes are the root causes of RCF. The axle load transfer among axles, which is aggravated by oblique traction rods, and inappropriate electrical compensation, and the curving behavior determine the axle preference of RCF on Type B locomotives. This explains the phenomenon that similar RCF damage has not been reported on Type B locomotives running in mild environments. At the end, the electrical compensation is optimized numerically with a purpose of easing RCF damage of Type B locomotives.

Study on the residual stress distribution of railway rails

Rolling contact fatigue damage of rails is significantly influenced by residual stresses. A three-dimensional elastic-plastic finite element model of wheel–rail contact was established in the present study, and the influence of initial stresses resulting from rail manufacturing process on the residual stress distribution of rails was analyzed. The repeated rolling passes were simulated and the stable residual stress distribution of rails was obtained. The influence of factors, such as wheel load, friction coefficient, and longitudinal creep rate, on the residual stress distribution of rails was investigated. It is found that within the limited special scale affected by the wheel–rail contact, the difference between the longitudinal residual stress with initial stresses applied and that without initial stresses applied becomes quite small once enough rolling passes have occurred (i.e., 10 rolling passes). When the initial stresses are applied, the longitudinal residual compressive stress on wheel–rail contact center of the rail is approximately 500 MPa. The residual compressive stress decreases with the increasing depth and changes from compression to tension at the depth of 6 mm beneath wheel–rail contact center of the rail. The wheel load mainly affects the residual stress distribution along the depth direction beneath rail surface. The friction coefficient mainly affects the residual stress distribution on the rail surface. The longitudinal creep rate has a great influence on the longitudinal residual stresses at the surface and along the depth of the rail.