Rolling Contact Fatigue Cracks Research Articles

Characterization of Angular RCF Cracks in a Railway Using Modified Topology of WPT-Based Eddy Current Testing

Unavoidably, rolling contact fatigue (RCF) causes natural crack formation in the railhead, leading to rupture. Eddy current testing (ECT) is commonly used to quantify RCF cracks because of its higher sensitivity to a surface flaw, though with limited feature points. This article aims to characterize inclined angular RCF crack parameters in a rail-line material via a modified topology of Wireless Power Transfer (WPT)-based ECT (WPTECT) due to its magnetically coupled resonant for excitation and sensing circuits and utilize multiple resonance responses compared to other ECT. We experimentally designed and evaluated WPTECT and extracted multiple resonances and principal components analysis features to characterize inclined angular RCF cracks. The response minima point feature quantified the crack parameters incomparably; however, the second resonance feature is better than the first resonance. The reconstructed depth, opening width, and angle of the RCF cracks have a maximum correlation, R²-value of 96.4%, 93.1%, and 79.1%, respectively, and RMSE of 0.05mm, 0.08mm, and 6.6⁰, respectively.

Out-of-round railway wheels and polygonisation

Out-of-roundness in railway wheels, in particular polygonal wear resulting in regular, multi-lobed, out-of-round wheels, has become a significant problem in recent years. It is of concern to railway operators due to the increased noise and vibration it can cause. This polygonisation is caused by cyclic wear but the exact mechanism leading to this type of wear is not fully understood. It appears to be the result of dynamic linking between a resonance or other periodic excitation in the coupled vehicle–track system and the existing wear at the wheel. This paper reviews the developing body of research being carried out in many countries by research groups, manufacturers and operators. Some examples of polygonisation on different types of railway vehicles are reported including feight trains, urban transit trains and high-speed trains. The main theories for the formation mechanisms are presented and the current measurement methods, computer simulation techniques and the effects and potential mitigation methods are reviewed. In parallel, the mechanisms and consequences of discrete wheel tread irregularities, such as wheel flats and material fall-out due to rolling contact fatigue cracking, are addressed.

A study on the rolling contact fatigue mechanism of ZC-L cast wheel steel

In this paper, the rolling contact fatigue (RCF) failure mechanism of ZC-L cast steel wheels was analyzed by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscope (TEM). The results show that obvious fatigue flaking is formed on the macroscopic surface of the wheel tread after RCF failure. The RCF cracks are formed at the maximum shear stress region of the sun-surface of the wheel (1–5 mm below the tread). There are a lot of subsurface white etching microstructure (WEM) and obvious casting defects in the subsurface of the wheel tread. The RCF cracks are mainly formed at the interface between the subsurface WEM and the matrix and at the edge of the casting defects. The subsurface WEM is composed of nano-ferrite grains and residual cementite, and its hardness is about 920HV, which is much higher than that of the matrix structure. During the wear process, the plastic deformation of the subsurface WEM and the matrix is not coordinated, resulting in the formation of RCF cracks. As a hard phase, the hardness of casting defects is much higher than that of matrix. In the process of wear, under the action of subsurface stress, the casting defects can cause obvious plastic deformation in the soft orientation region at the edge of the casting defects. When the plastic deformation reaches the plastic limit, the RCF cracks are formed at the edge of the inclusions due to ratchet failure. The stress at the crack tip is caused by the RCF crack propagation at the edge of inclusions will further lead to the refinement of the microstructure at the edge of the RCF crack. Under the action of the subsurface contact stress, the subsurface WEM and casting defects are the main reasons leading to the RCF failure of the ZC-L casting wheel. Improving the microstructure uniformity and reducing casting defects are the main methods to improve the fatigue property of casting wheels.

Wear and rolling contact fatigue competition mechanism of different types of rail steels under various slip ratios

This study aims to explore the wear and rolling contact fatigue (RCF) competition mechanism of the hypoeutectoid, eutectoid rail, and bainitic rail steels under different slip ratios. The results showed a clear competition relationship between wear and RCF of rail steel. With the increase in slip ratio, the wear rate of hypoeutectoid and eutectoid rail steels was increased and then remained stable, and the wear rate of bainitic rail steels was increased. Bainitic rail steels suffered catastrophic wear when the slip ratio exceeded 2%. With the slip ratio increased, the RCF crack propagation rate of the hypoeutectoid rail and eutectoid steels rail increased rapidly at first and then increased slowly. Except for the slip ratio of 5%, the RCF crack propagation rate of the bainitic rail increased with the increase in slip ratio. With the increase in slip ratio, the degree of wear rate increase and crack propagation rate was not consistent, which led to the competition between wear and RCF. The competitive relationship between wear and RCF was reflected in the variation of rail wear form. As the slip ratio increased, the main wear form of the hypoeutectoid and eutectoid rail steels was transformed from adhesive wear to adhesive wear and fatigue wear, whereas for bainitic rail steel, it was changed from adhesive wear to fatigue wear, and finally to adhesive wear. At high slip ratios, the retained austenite of bainite rail steel was seriously broken, so cracks in the bainitic rail steel could easily propagate along the plastic deformation layer.

Investigation of Quantitative Evaluation of Rolling Contact Fatigue Cracks in Rail Steel by X-Ray Diffraction Line Profile Analysis

Investigation of Quantitative Evaluation of Rolling Contact Fatigue Cracks in Rail Steel by X-Ray Diffraction Line Profile Analysis

Effect of normal load on the wear and rolling contact fatigue behaviour of AAR class B wheel against R350HT rail in a twin disc simulator

The normal load at the wheel-rail contact interface plays a significant role in wear and rolling contact fatigue (RCF) performance of both wheel and rail steels. In recent years, there has been an increase in axle loads due to increased demand for railway services. This study investigated the effect of normal load on the wear and RCF behaviour of the AAR class B wheel versus R350HT rail using a twin disc wear simulator. The mass loss, surface damage and depth of deformation were used to assess wear and RCF, respectively. From the mass loss results, wear maps were obtained to identify different wear regimes being mild, severe and catastrophic at different contact loads and slip ratios. Scanning electron microscopy was also used to assess the surface damage of wheel and rail steels in order to identify the wear regimes with surface cracking and delamination being observed at higher contact loads indicating severe and catastrophic wear. Furthermore, the RCF crack density was found to be higher on specimens evaluated at higher normal loads with more cracks evident and crack branching forming.

Investigation on the interaction between corrosion and wear of U68CuCr rail steel with different corrosion periods

The interaction between corrosion and wear of U68CuCr rail steel was investigated. The samples were alternately subjected to the neutral salt spray tests with different corrosion periods (6, 24 and 48 h) and rolling friction wear test for 4 h. The corrosion and wear rates after the corrosion test and wear test were measured, respectively. The surface morphologies of the rail samples after the corrosion test and wear test, and the subsurface morphologies of the rail samples after the last test were observed. The results show that compared to the samples without corrosion, the damage degree of the corroded samples after wear tests became severer, and the wear mass loss and wear rate increased with the number of corrosion-wear cycle. In addition, rolling contact fatigue cracks initiated and propagated at a high angle and the structure of sample surface became unstable after corrosion, leading to easy spalling during the following wear tests compared to the only wear tests without corrosion. Moreover, the plastic deformation layer was destroyed by corrosion and the area of wear pits increased after the interaction test. Therefore, wear was accelerated by corrosion, and the longer is the corrosion period, the more severe is the wear degree. Additionally, regarding to the effect of wear on corrosion, corrosion was accelerated by wear. This is attributed to the facts that (1) the wear pits and delamination on the worn samples provided favorable locations for the deposition of the salt spray solution during the corrosion, and (2) the subsurface and matrix were corroded along rolling contact fatigue cracks to increase the corrosion rate during the corrosion test after wear. This work provides a foundation to the further investigation on the interaction between corrosion and wear of steels.

Prediction of rolling contact fatigue crack propagation in bearing steels using experimental crack growth data and linear elastic fracture mechanics

Rolling contact fatigue (RCF) is a major life limiting factor for machine elements that employ non-conformal, rolling sliding, lubricated contacts such as rolling bearings and gears. This paper explores the application of linear elastic fracture mechanics (LEFM) principles, as commonly used in structural fatigue, for prediction of RCF crack propagation. A triple-disc contact fatigue machine is used to generate RCF cracks of varying lengths in AISI 52100 bearing steel roller specimens. Crack propagation rates across the surface are measured using optical inspection of test specimens and the final crack geometry is established through specimen sectioning. A numerical finite element model of surface breaking RCF cracks based on LEFM methods is devised to predict the evolution of stress intensity factors (SIFs) during over-rolling of the contact over the experimentally observed crack geometries. The model employs a suitable fracture mechanics mesh to resolve stresses at the crack tip and accounts for Hertzian contact stresses, contact friction and crack face friction. Potential effects of lubricant pressurisation within the crack are not modelled. The predicted SIFs are then related to the experimentally measured crack propagation rates to establish the applicability of the LEFM principles to RCF crack propagation. Results show that LEFM can be used to predict the growth of surface braking RCF cracks. For cracks longer than about 100 μm, a Paris law relationship with the stress intensity exponent of about 4 is derived. Mode II was seen to be the dominant mode of propagation for surface braking RCF cracks. Mode I SIFs are much smaller but can exhibit significant values when the contact is located just ahead of the crack mouth. Decreasing the crack face friction significantly increases mode II stress intensity suggesting that this is one important mechanism by which lubricant entry into the surface braking crack can accelerate its propagation. The findings can help in improving the reliability of mechanical systems by supporting the development of new tools for prediction of remaining useful life of machine components such as bearings and gears.

Nondestructive analysis of rolling contact fatigue cracks using induced scanning thermography.

Rolling contact fatigue (RCF) produced by wheel-rail interaction is now considered to be a critical factor that causes failure. Throughout this work, induced scanning thermography (IST) for detecting RCF defects at different depths is investigated. The original thermal sequences could not utilize the features at the heat dissipation stage; thus, a data reconstruction method, including principal component analysis (PCA) and Tucker factorization, was employed to extract the spatial and time patterns. In addition, detectability was evaluated across a range of speed studies. The Tucker-PCA combination algorithms obtained defects with improved quality, showing a clear boundary over the velocity range of 1-4km/h, which dramatically suppressed background noise. A unique gradient response characteristic in the cooling phase was summarized and utilized through experimental verification in order to recognize defect width.

Wheel wear and rolling contact fatigue evolution under interaction of abrasive block and wheel–rail contact: results from field test

ABSTRACT Wheel transverse wear, irregular wear along the circumference (out-of-roundness), and rolling contact fatigue (RCF) are inevitable problems in the railway industry. One effective countermeasure to solve these problems is to apply a tread abrasive block (tread trimmer) that has the function of cleaning and repairing the wheel treads. In this study, to investigate the effect of abrasive blocks on wheel wear and RCF, five working modes of the abrasive block were designed for an urban express train operating on an urban express line in China. The wheel profiles, wheel out-of-roundness, and abrasive block profiles of the urban express train were monitored. The results show that the low-pressure and intermittent modes of the abrasive block can suppress wheel polygonal wear, eliminate hollow wear with acceptable tread wear, maintain equivalent conicity at a good level, reduce the wear of the abrasive block itself, and remove RCF cracks.

XFEM rolling contact fatigue crack propagation in railways considering creepages on contact shear stresses

In this work the influence of considering wheel-rail contact creepages on fatigue crack growth rates due to Rolling Contact Fatigue(RCF) is studied. For this purpose, the FASTSIM algorithm, which considers the moving complex pressure distribution with slipping and adhesion zones of the wheel-rail contact patch, has been implemented in Abaqus using FORTRAN code subroutines. The developed methodology has been validated with a 60E1 rail profile model which uses XFEM, by comparing the obtained Stress Intensity Factors(SIFs) and sub-surface shear stresses with numerical results available in the literature. Finally, the RCF crack propagation analysis of a 60E1 rail profile with different contact conditions has been performed using the XFEM. The obtained results justify the necessity of considering contact creepages on contact shear stresses for crack growth analysis.

Numerical modeling of rolling contact fatigue cracks in the railhead

Rolling contact fatigue (RCF) crack is one of dominating damages on the rail surface due to repeated wheel and rail contact. RCF defects, including squats and head checks, can potentially cause rail fracture failure if not treated in time. It is critical to accurately predict the pertinent damage for different operational conditions. A two-stage simulation strategy was proposed to investigate the mechanisms of RCF-induced cracks on the rail, consisting of a dynamic FEM for wheel and rail interaction and a coupled static FEM/BEM for crack growth. It was found that there are two critical wheel positions for crack propagation during wheel approaching to and departing from the pre-existed crack. The different cracking mechanisms at these two critical wheel positions are correlated with the local physical phenomena, i.e., the traction at the wheel/rail interface, the relative distance between the contact patch and crack, and the sliding at crack faces. The twisting of the cracks from the transverse plane to the longitudinal plane at the railhead significantly reduces crack growth in mode I, enhances crack propagation in modes II and III, and shifts the dominant crack growth from the crack front center to the crack corners. The increased incline of the crack in the rolling direction promotes the crack to grow downward in opening mode I.

Comparison of Rail Head Checks Using Destructive and Non-Destructive Examination Methods

The development of railway transportation requires increased vehicle speeds and axle loads. The enhanced effects from the vehicle side and the new harder steel rails used in tracks lead to increased Rolling Contact Fatigue (RCF) crack initiation and propagation. One of the most frequently occurring RCF defects is the Head Checks (HC) around the rails’ gauge corner. These defects cause severe economic and safety issues. In-use maintenance is based on corrective and preventive approaches, which are neither cost-effective nor reliable. The development of new predictive methods and the improvement of the existing corrective and preventive approaches offer a solution to this issue. In this investigation, an HC-infected rail sample was examined with non-destructive Dye Penetration Testing, Eddy-current Testing, and Visual Microscopic Testing after the sectioning of the sample. In the future, an extensive HC database can be created from the results of the developed evaluation process, which may serve as the base validation tool for newly developed predictive maintenance methods.

A novel SAM/X-FEM coupling approach for the simulation of 3D fatigue crack growth under rolling contact loading

The present work proposes a novel efficient numerical approach for the simulation of three-dimensional propagation of non-planar frictional crack under Rolling Contact Fatigue (RCF). The developed model relies on a global–local strategy involving the Semi-Analytical Method (SAM), dedicated to the resolution of 3D contact problems, and the eXtended-Finite Element Method (X-FEM), dedicated to the solving of 3D crack problems. Similar to a submodeling technique, it consists in performing a local X-FEM analysis of the 3D RCF crack problem by means of boundary conditions extracted from a prior global SAM analysis which solves the contact problem between two semi-infinite bodies without considering the crack. A powerful procedure for the transfer of relevant mechanical quantities between the SAM and X-FEM models is developed. It allows the use of non-matching and non-conforming discretization scheme for the global SAM model and the local X-FEM model, particularly worthwhile for the pre-processing stage. An initial arbitrary stress profile can be considered to investigate the influence of residual stresses on crack behavior. The non-intrusive SAM/X-FEM coupling is integrated into a fully automatic crack propagation algorithm. This provides a powerful and user-friendly tool suitable for industrial applications, which easily handles 3D long non-planar frictional crack growth in the region of interest. After introducing some details concerning the implementation of the model, a validation of the innovative SAM/X-FEM coupling is performed by using results from the literature. Furthermore, a practical example demonstrates the great potential of this novel numerical technique to simulate in a fast, robust and accurate way the 3D complex behavior of fatigue crack under moving contact. • Simulation of the 3D frictional crack propagation under rolling contact conditions. • Non-intrusive global–local approach based on the coupling of SAM and X-FEM. • Field transfer procedure allowing independent meshes for the SAM and X-FEM models. • Fast, efficient and robust resolution coupled with a pre-processing time saving. • Influence of residual stresses on crack behavior highlighted.

Implications of water medium for the evolution of rolling contact fatigue under rail surface defect conditions

With existing rail surface defects, third body mediums play an important role in the evolution of Rolling Contact Fatigue (RCF). This study investigates the effect of water mediums on the evolution process of RCF behavior on defective rails. Conical artificial defects were created using an indentation apparatus and wheel-rail rolling contact tests were conducted on a twin-disc test machine. Results indicate that rolling test preparation procedures can affect the development of RCF behavior of the rail material with surface defect under water condition. The morphology from cross-section views under water condition can be divided into four regions due to various RCF behavior evolution based on relative locations from surface defects. However, in all regions, average crack depths, densities and damage degrees increased first and then decreased with the progress of the tests. Damage in areas with and without pre-existing defects under water and dry conditions were compared and discussed. Results also show that the ratio between the remained defect depth and the RCF crack depth would determine whether the existence of defect influence the RCF behavior on the rail material.

Investigation into the evolution of tribological white etching layers

When wheels and rails are in operation, their complicated and changeable contact conditions contribute to the formation of white etching layers on their contact surface. Martensite white etching layers (M-WELs) can induce the initiation of rolling contact fatigue (RCF) cracks, accelerating wheel/rail failure; Tribological white etching layers (T-WELs) can improve wear resistance. Therefore, to investigate the formation of T-WELs is to provide theoretical bases for developing surface strengthening technology. In order to delve into the mechanism for the formation of T-WELs, this paper conducted dry friction sliding wear experiment on ingot iron (equiaxed ferrite), D1 wheel steel (lamellar eutectoid ferrite) and FCB wheel steel (lath-like bainite-ferrite), and generalized the impacts of ferrite with different morphology and the second phase on the evolution of T-WELs. The result showed that T-WELs formed on the worn surfaces of all of these materials under the condition of sliding wear, and the evolution of T-WELs displayed similarities. Under the impact of dislocation slip mechanism, size reduction and dimension reduction were realized and finally ultrafine ferrite grains formed. But the second phase would increase the critical shear stress value of the transformation of ultrafine ferrite grains, hindering the formation of T-WELs and eventually affecting the size of ultrafine ferrite grains inside T-WELs.

Rolling contact fatigue crack propagation on contact surface and subsurface in mixed mode I+II+III fracture

Rolling contact fatigue (RCF) is the critical damage from rolling bearings constraining the service, performance, and reliability, which is directly caused by fatigue crack propagation. The crack paths on both the contact surface and subsurface were observed after the bearing fatigue test. The three-dimensional geometry of the RCF crack was characterized and reconstructed based on experimental statistics. Finite element analysis was performed to obtain the mixed mode stress intensity factors (SIFs) along the crack fronts, and the crack propagation behavior was numerically studied. Results indicated that the propagation of cracks on the contact surface and subsurface causes the gradual formation of micropits and the sudden spalling of material respectively. Initial micro-cracks with an inclination angle of 15–30° have the highest growth rate, which should be prevented during the bearing raceway manufacturing process. The propagation paths of the RCF cracks can be more accurately predicted by considering the superposition of fracture mode I + II + III in three-dimensional, and mechanisms of crack propagation on contact surface and subsurface were revealed respectively.

Crack path investigations in a pearlitic rail steel after pre-deformation under cyclic Mode-II loading

The crack path under cyclic Mode-II loading in undeformed and pre-deformed pearlitic rail steel R260 is investigated. To produce large-scale specimens with pre-deformed microstructures two methods are applied. Firstly, cylinder bars are processed using an axial-torsion machine resulting in a moderate deformation. Secondly, a new high pressure torsion (HPT) setup is developed to achieve a more strongly deformed microstructure. In the fatigue tests, a distinctive change in the crack path is observed. In the undeformed and moderate deformed specimens, the cracks bifurcate and turn into a Mode-I dominated mixed-mode. In the HPT material, the cracks grow in Mode-II without mixed-mode propagation. For rolling contact fatigue cracks in rails these experimental results indicate a strong connection between the propagation mode and the anisotropy of the highly deformed pearlitic microstructure. This microstructure is characteristic near the wheel-rail contact surface. In future, these findings are important to improve numerical-based crack growth prediction models.

Differential ECT Probe Design and Investigation for Detection of Rolling Contact Fatigue Cracks With Different Orientations

Eddy current testing(ECT) is widely applied to detect surface defects on metallic materials. In ECT for cracks on complex curved surfaces, immunity to lift-off and the detection ability of the eddy current probe are critical challenges. In this study, we designed and developed a novel differential transformer ECT probe using AD698 signal conditioning to detect cracks with different orientations in rail treads. It adopts flexible printed circuit board (FPCB) technology for complex curved surfaces. The new ECT probe consists of four-square driver coils and two 8-shaped pick-up coils with antiserial connections that can sense opposite magnetic field changes in different directions. The proposed probe can solve the detection ability and lift-off problem of crack with different orientation on complex curved surfaces. The theoretical analysis which is based on transformer principles, is described in this paper. The detection ability of the new probe at different frequencies was evaluated by numerical simulation. Upon completion, the numerical simulations analyzed the effects of crack with different orientation and lift-off on the detection ability of the proposed probe. The experimental system was built to verify the detection ability of different crack with different orientations and immunity to lift-off by the proposed probe. The results of the simulation and experiment indicated that the proposed probe has a good ability to detect crack with different orientation whereas its performance decreases as crack orientation increasing. The proposed probe can also substantially suppress lift-off noise.

Analysis of the RCF crack detection phenomenon based on induction thermography.

Eddy current pulsed thermography (ECPT) is used to detect rolling contact fatigue (RCF) cracks on the rail. It is observed that some of the cracks disappear in the thermal image with the increase of heating time. Based on the finite element method, with double cracks as the basic unit, three different crack models are established, and the mutual disturbance relationship between the double cracks is discussed based on the eddy current distribution and thermal diffusion process. The simulation and experimental results show that different crack models are affected by thermal diffusion in different heating stages to different degrees, and the time of the crack thermal image disappearance is obtained. According to the above conclusions, the RCF cracks are extracted and classified based on the influence of thermal diffusion. The possibility of rail condition assessment and maintenance based on the disappearance time is explained.