Rolling Contact Fatigue Research Articles

Eddy Current Sensor Array for Electromagnetic Sensing and Crack Reconstruction with High Lift-Off in Railway Tracks.

A reliable and efficient rail track defect detection system is essential for maintaining rail track integrity and avoiding safety hazards and financial losses. Eddy current (EC) testing is a non-destructive technique that can be employed for this purpose. The trade-off between spatial resolution and lift-off should be carefully considered in practical applications to distinguish closely spaced cracks such as those caused by rolling contact fatigue (RCF). A multi-channel eddy current sensor array has been developed to detect defects on rails. Based on the sensor scanning data, defect reconstruction along the rails is achieved using an inverse algorithm that includes both direct and iterative approaches. In experimental evaluations, the EC system with the developed sensor is used to measure defects on a standard test piece of rail with a probe lift-off of 4-6 mm. The reconstruction results clearly reveal cracks at various depths and spacings on the test piece.

Strain‐Induced Martensitic Transformation and the Mechanism of Wear and Rolling Contact Fatigue of AISI 301LN Metastable Austenitic Stainless Steel

AISI 301LN metastable austenitic stainless steels (MASSs) are known to exhibit high work‐hardening rates attributed to martensite evolution during straining which results in the second‐phase strengthening mechanism. This enhances surface hardness and potentially reduces wear and rolling contact fatigue (RCF). The aim of this study is therefore to evaluate the work hardening, wear, and RCF performance of AISI 301LN metastable austenitic stainless steel as a possible alternative material for rolling and sliding applications by varying the contact conditions such as slip ratio against the standard R350HT rail steel using a twin‐disc simulator. The results show that 301LN MASS has high surface work hardening and increased hardness because of martensitic transformation, while R350HT rail steel has only slightly changed. The formation of a hard martensitic phase is also confirmed by X‐ray diffraction analysis as well as by two other techniques, indicating a secondary hardening effect. Although it shows potential for work hardening, its susceptibility to wear‐related problems may make it less suitable for rolling and sliding applications due to a cracking and spalling mechanism induced by martensite formation. The surface strains required for the observed martensite formation are calculated and found to be very high, approaching 0.4.

Study on rolling contact fatigue crack initiation and propagation in U75V rail treated by laminar plasma

Surface discrete hardening by laminar plasma (HLP) enhances rail wear resistance by rapidly quenching surfaces to form discrete martensitic zones. In comparative field tests on a North China freight railway, HLP-treated U75V rails supported twice the total passing weight before reaching wear limits, compared to untreated rails. However, HLP treatment increases susceptibility to rolling contact fatigue (RCF) cracks, including interface cracks from mechanical differences, impact cracks from wheel-rail contact, deformation cracks from cumulative deformation, and matrix cracks extending from interfaces. The ratchet effect and seesaw mechanism, due to plastic deformation accumulation and quenching area warping, are crucial for crack initiation and propagation. This research advances understanding of HLP-treated rails' tribological behavior, emphasizing the necessity for customized maintenance strategies.

An efficient 3D finite element procedure for simulating wheel–rail cyclic contact and ratcheting

Various models for simulating rail ratcheting behaviour were developed to study rolling contact fatigue (RCF) damage in rails. However, limitations remain in terms of the accuracy of wheel–rail contact modelling and computational efficiency of the cyclic loading simulation. This study developed an efficient 3D finite element (FE) procedure to simulate ratcheting in rails subjected to numerous load cycles. The procedure simulates a wheel rolling repeatedly over a rail section with updated stress–strain states, enabling automatically executed cyclic loading simulation given a predefined number of cycles. To ensure the accuracy of the contact modelling, the effect of meshing schemes on subsurface stress distribution was examined. In addition, the FE contact model with the selected meshing scheme, which balances accuracy and computational efficiency, was verified against the widely accepted CONTACT program. Subsequently, a non-linear kinematic hardening (NLKH) steel material was used in the FE model for ratcheting simulations with up to 100 wheel-loading cycles. The rail surface and subsurface stress states were replicated under partial-slip wheel–rail rolling contact conditions with traction coefficients of 0.10, 0.20 and 0.35, respectively. The ratcheting behaviour was extensively analysed in terms of plastic deformation, contact patch evolution, and ratcheting rates. The simulated plastic deformation was found to alter the contact geometry and thus contact stresses, which in turn affect further accumulation of plastic deformation and subsequent ratcheting strains. These findings highlighted the importance of considering the interplay between the rail ratcheting behaviour of the rail and evolving contact conditions for predicting ratcheting and RCF damage in rails.

Capacity assessment of railway axle journal bearing addressing a localized rolling contact fatigue failure mechanism

Abstract A framework for assessing the capacity of railway axle journal bearings is presented after elaborating on the locale rolling contact fatigue (RCF) failure mechanism. Three phases are conducted, including the determination of bearing service loads, finite element analysis (FEA) on the localized RCF stresses of bearing components, and the life-related capacity assessment on the bearings and bearing components. Results prove that wheel-track (WT) contact forces inspected by an instrumented wheel set can be transferred into bearing service loads. Two-step FEA from the global wheel set to the local bearings is used to obtain localized RCF stresses at dangerous locations around the bearing contact regions. After determining the locations, a life-related capacity assessment is performed by evaluating equivalent RCF stresses and lives at the locations to determine the weakest bearing component. Typical practice is given in agreement with FEA. This method deals with the FEA of bearing structures, material cyclic stress-strain curves, and probabilistic RCF life curves. Therefore, this work greatly enhances the development of rail-bearing materials, innovative structures, and capacity assessment.

Comparative analysis of rolling contact fatigue life in a wind turbine pitch bearing with different modeling approaches

The load calculation for wind turbines usually does not take pitch bearings into account, and the pitch-bearing internal load distribution is calculated in a decoupled process. In the current study, a coupled wind turbine load simulation considering the pitch bearings is proposed. Internal pitch-bearing load distribution and roller contact fatigue life are compared to a decoupled approach using a high-fidelity finite-element model. Internal pitch-bearing load distribution can be an essential variable in almost all major pitch-bearing failures. Furthermore, rolling contact fatigue is one of the major types of pitch-bearing failure that can represent the bearing service life. The results show that the flexibility of the surroundings has an effect on the contact forces. As a result, the finite element model-based life calculation of the NREL 5 MW turbine predicts a longer rolling contact fatigue life for the bearing than the multi-body system-based one. For the IWT7.5, sample load cases indicate that this behavior is different, leading to the conclusion that the life of the bearing is significantly affected by the stiffness of the bearing and its surrounding components.

Investigation of plastic flow of rail vehicle wheels and its effects on rolling contact fatigue based on a dynamic method

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

The effect of fine particle peening on aviation gear performance, part II: Rolling contact fatigue

AbstractFine 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.

Relating rolling contact fatigue (RCF) life to the microstructure evolution in aerospace grade bearing steels: A comparison of Cronidur-30 with AISI 440C

This article presents an extensive analysis of the microstructural evolution under various heat treatment conditions, mechanical properties (hardness), and rolling contact fatigue (RCF) life assessment and sub-surface crack analysis are studied on high nitrogen bearing steel Cronidur-30(Cr-30). An optimum solutionising temperature range has been identified which ensures desirable hardness as well as low retained austenite content. The microstructure consists of primary M2 (C, N) and secondary M23C6 carbides. Sizes of carbides in Cr-30 are significantly smaller than in AISI 440C and this plays a critical role in enhancing the RCF life of Cr-30. A larger area fraction of fine carbides results in branches and subsequent sub-branches of cracks in Cr-30 steel. However, the AISI 440C sample exhibits extensively interconnected cracks due to the presence of larger carbides. The tempering response of Cronidur-30 exhibited a peak hardness of 61 HRC at both lower (150 °C) and higher (475 °C) temperatures. Higher temperature tempering showed L1 life improvement of over 0.5 fold compared to lower temperature tempering.

Crystal plasticity modeling of grain boundary softening and fatigue in U75V pearlite steel under low strain conditions: A study of cyclic rolling contact fatigue

Grain boundaries (GBs) exhibit fatigue-induced softening under low strain conditions, making them the weakest and most vulnerable regions within the material. This phenomenon significantly influences plastic deformation, plastic strengthening, and the initiation and propagation of microcracks, leading to material fatigue failure. This investigation presents a comprehensive model for the rolling contact fatigue (RCF) damage mechanism of U75V railway steel. Leveraging data from Electron Backscatter Diffraction (EBSD) and employing the Crystal Plasticity Finite Element Method (CPFEM), intragranular mechanical responses are elucidated. A modified bilinear Traction Separation Law (TSL) Cohesive Zone Model (CZM) is developed to capture the impact of GBs fatigue. Integrating this CZM with CPFEM, mechanical properties, scalar stiffness degradation (SDEG), fatigue damage factors, and crack evolution patterns are analyzed to explore the effects of grain morphology, orientation, GB angle, and area on GB fatigue damage and crack initiation. Results indicate a significant increase in GBs damage with increasing GBs angle or decreasing GBs area, highlighting the potential for reducing RCF damage through deliberate grain morphology design. Additionally, GBs are found to impede crack propagation, suggesting that grain refinement can mitigate crack propagation rates. This study enhances our understanding of intergranular fracture, mechanical responses, and microstructure evolution in U75V rail steel under cyclic rolling contact loading, offering novel methodologies for investigating metallic materials' deformation behavior concerning GB fatigue.

Track Deterioration Model—State of the Art and Research Potentials

Track deterioration models (TDMs) help to allocate maintenance work (direct costs) to vehicle runs. Furthermore, these models demonstrate the impact of rolling stock properties on infrastructure. This paper review provides an overview of the state of the art in railway track deterioration modelling and outlines the research potential in this domain. The main focus lies on ballast degradation, rail surface wear and fatigue, and their description in an empiric analytic wear formula. The basis for discussion is the wear formula of the Graz University of Technology. While the TDM demonstrates effectiveness, enhancements are sought, particularly with regard to adjusting the track parameters that vary across railway networks. Further exploration aims to refine the description of rail surface wear and rolling contact fatigue (RCF), incorporating factors such as traction energy and short-wave effects and adapting mathematical functions such as the t-Gamma function. This review underscores the need for ongoing research to develop TDMs that are both simple and detailed enough to encourage track-friendly rolling stock design.

Surface integrity and rolling contact fatigue behavior of 18CrNiMo7-6 steel subjected to ultrasonic surface rolling process

In this study, the effect of ultrasonic surface rolling process (USRP) on the surface integrity and rolling contact fatigue (RCF) behavior of 18CrNiMo7-6 steel have been conducted. The different static loads and ultrasonic amplitudes on surface morphology, surface roughness, microstructure, microhardness, and residual stress were examined. Results revealed that USRP treatment resulted in a remarkably smooth surface with the surface roughness value Ra of 0.035 μm. Moreover, USRP treatment induced the formation of nanocrystalline and ultrafine crystalline structures on the surface layer. Additionally, the sample surface was subjected to a significant layer of residual compressive stress, reaching a maximum value of approximately −1243 MPa and extending to a depth of around 1500 μm. The surface microhardness had been increased to 808 HV0.2. The comprehensive integration of grain refinement, the increase of surface microhardness, and the induction of residual compressive stress led to an improvement in RCF life.

The effect of retained austenite on rolling/sliding contact fatigue of high carbon steel

Rolling contact fatigue (RCF) is significantly influenced by retained austenite (RA). To study the impact of the RA on fatigue life and pit formation, a high carbon steel was tested with three different RA levels ranging from 5 % to 23 % (volume fraction). The variations of the RA with respect to the number of cycles and along the depth were inspected by X-ray diffraction (XRD) technique. The microstructures before and after RCF were characterized by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The majority of RA was transformed into martensite at an early stage (before 3 × 104 cycles) in both surface and subsurface. And the remaining small fraction of RA was transformed during the rest of the testing life, with a final content lower than 5 %. As the depth increased, the rate of RA transformation decreased. The specimen with the highest RA level of 23 % showed the shortest life. The longest RCF life was seen in the specimen with a medium RA level of 15 % due to the formation of the well-developed hardened layer, which helps resisting the pit formation. Based on these observations, it was suggested that a medium level of RA is beneficial for the improvement of the RCF life of the present high carbon steel. The combined effect of the hardness and the RA acts together on resistance to pit formation.

Effect of surface rolling process on rolling contact fatigue behavior and failure mechanism of powder metallurgy steel

The effect of surface rolling process on the surface microstructure and rolling contact fatigue of the Fe-2Cu-0.6 C powder metallurgy steel was investigated in the present investigation. Results indicated that a densified and hardened layer with a densification depth of 330 μm and a surface hardness of 330 HV0.1 was generated in the surface layer after rolling process. Ferrite grain and pearlite lamellae became typical fibrous structures on the top surface. The microstructure of pearlite was presented by two typical features. One was that the discrete cementite plates were severely curled and wavy. The other one was that the cementite plates remained parallel to each other, but were a reticular structure at a macroscopic level. The rolling contact fatigue (RCF) test showed that the RCF life of the rolled sample was superior. The L10, L50, L63.2 life increased by 182%, 105%, 92%, respectively. Surface initiated spalling was the main fatigue failure mode. Subsurface equivalent contact stress and local equivalent stress were calculated. The results showed that surface cracks were due to the repetitive tensile stress, which caused pits. Subsurface cracks nucleated and propagated in the region where the local equivalent stress was higher than the matrix yield strength, which caused spalling as connecting with surface cracks. The surface densified layer plays an important role in improving the rolling fatigue resistance of the material.

An investigation into Belgrospi-like damage formation on a sharp curved track using finite element method

Belgrospi-like damage is a special type of rolling contact fatigue (RCF) characterized by periodically grouped crack nests with short-pitch corrugation, which has been observed on sharp curved track in China. A 3D finite element model of the elastic–plastic wheel–rail transient rolling contact on a sharp curved track is developed to investigate the dynamic rolling interaction on corrugated rail. The competitive relationship between wear and RCF under cyclic loading is evaluated. Important findings include that the slope of corrugation geometry (CG) causes the center of the upslope the greatest dynamic contact solutions, which have a phase lead with respect to the CG. Under long-term cyclic loading, the rail material failure due to the continuous accumulation of plastic shear strain is RCF.

The role of microstructure on the wear and rolling contact fatigue of railway steels: The performance of bainite

This study aims to describe the wear and rolling contact fatigue (RCF) behavior of microalloyed forged railway wheel steel Class D (7NbMo), with microstructures of upper bainite (UB - 350 HV0.5), lower bainite (LB - 450 HV0.5), and pearlite (PE - 350 HV0.5), against 7C steel with a tempered martensite microstructure (660 HV0.5) in a twin-disc tribometer. The results showed that bainite (LB and UB) exhibited greater wear resistance compared to pearlite (PE). The primary wear mechanism for all three microstructures was the fatigue wear. An analysis of the PE disc revealed continuous (single-layer) RCF cracks, which were relatively large and deep. In contrast, UB and LB cracks were discontinuous (multiple layers), thin, and smaller but more numerous (higher crack density). These characteristics indicated that bainitic microstructures also had greater resistance to RCF than pearlite did. Therefore, the combination of mechanical properties and the morphological arrangement of the microstructure led bainite to develop a shallower depth of deformed layer with a higher capacity for plastic deformation per unit volume. The greater wear and RCF performance of bainite compared to those of pearlite may be associated with how they release the accumulated deformation energy after reaching saturation in relation to volume deformation absorption: regarding bainite, the material releases energy by opening crack surfaces; conversely, regarding pearlite, it is through the detachment of large and wide cracks.

Analysis of the Influence of Contact Stress on the Fatigue of AD180 High-Carbon Semi-Steel Roll

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.

Rolling contact fatigue analysis of the soft zone for the main bearing in a tunnel boring machine

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

Multi-objective optimisation of a metro wheel profile to reduce wheel flange wear and RCF considering the distribution density of wheel−rail contact points

In this study, the problem of severe wheel flange wear and tread rolling contact fatigue (RCF) of metro wheels with two wheel profiles, i.e. the LM-30 profile and the DIN5573-30 profile, is investigated. The contact characteristics of the two profiles are compared to analyse the causes of wheel flange wear and RCF. Indices combining the density distribution of contact points are proposed to evaluate the wheel flange wear and RCF. The optimisation region of the wheel profile is defined by eight arc parameters, which is derived from the tangency of the arcs. A back-propagation neural network is constructed as a surrogate model for the design variables and the objective function. Four intelligent optimisation algorithms are compared and used to solve the optimisation problem. The vehicle—track dynamic model and the wheel wear and RCF prediction model are used to verify the performance of the optimised profile. The results show that the critical speed of the optimised profile is between that of the LM profile and that of the DIN5573 profile, and the curving performance of the optimised profile is significantly improved. At the same time, the optimised wheel profile can reduce wheel flange wear and tread RCF.

Micropitting performance and friction behaviour of DLC coated bearing steel surfaces : On the influence of Glycerol-based lubricants

A better understanding about the rolling contact fatigue and micropitting performance of machine component surfaces lubricated with environmentally friendly lubricants is critical to designing and further formulating new lubricants intended to be used in rolling–sliding contacts such as those found in gear and bearing applications. In this work, the frictional behaviour and rolling contact fatigue (RCF) performance of DLC, Cr/a-WC:H/a-C:H and a-C:Cr coatings under glycerol-based lubrication in rolling sliding contact conditions have been investigated. Traction maps, Stribeck curves, and fatigue plots have been generated by using a micropitting test rig (MPR). The initiation and progression of micropitting was monitored by means of white light optical interferometry and scanning electron microscopy (SEM). Results indicated that glycerol-based lubricants exhibited a significant friction reduction as the hydrodynamic effect is enhanced at higher rolling-speeds. Under boundary lubrication the friction coefficient was significantly higher compared to the values obtained with a commercial mineral-based transmission oil. Compared to uncoated steel surfaces, DLC coatings effectively reduced the volume loss and micropitting progression. Irrespective of the coating thickness, DLC showed an excellent tribological behaviour when the base lubricant favours the onset of mild-wear, over micropitting. When the lubricant formulation favoured the onset of micropitting, the coatings tended to prematurely fail due to debonding from the substrate, and local micro-spallation. The experiments demonstrated that friction reduction does not necessarily correspond with a reduction of micropitting.