Rolling Contact Research Articles

Fatigue Crack Propagation Analysis of Rail Surface Under Mixed Initial Crack Patterns

Prolonged rolling contact fatigue between wheels and rails results in the formation of surface cracks on the rail and accurately analyzing the crack expansion behavior is essential to ensuring the safe operation of the train. Drawing upon the principles of fracture mechanics and finite element theory, this study establishes a finite element model of wheel–rail rolling contact that incorporates the presence of cracks. The method utilizes an interaction integral to calculate the stress intensity factors at the leading edge of the crack; then, the Paris formula is used to solve the crack spreading rate. It systematically examines the effects of the initial crack angle, the coefficient of friction of wheels to rails, and crack size on the behavior of fatigue crack propagation. The results indicate that the cracks primarily extend in the depth direction of the rail, transforming the semi-circular surface cracks into elliptical cracks with the major axis oriented along the rail’s width. Crack propagation is primarily driven by model II and III composite crack propagation, with their expansion rates influenced by operating conditions. In contrast, mode-I expansion is less sensitive to these conditions. Under single-variable loading conditions, a smaller initial crack angle results in a faster crack growth rate. Increasing crack length accelerates crack growth, while a higher friction coefficient inhibits it.

Rolling contact fatigue failure mechanism with the multi-scale analysis of BG801 high temperature bearing steel

Rolling contact fatigue failure mechanism with the multi-scale analysis of BG801 high temperature bearing steel

Microstructure evolution and fatigue crack initiation life prediction of actual failed bearings under GRCF conditions

During the operation of bearings under alternating stress, contact fatigue failure often occurs, primarily due to non-metallic inclusions in bearing steel (GCr15). Based on actual fatigue-failed bearings, this study used Aspex scanning electron microscopy to analyze the inclusion distribution in bearing steels produced by two processes: electroslag remelting and vacuum refining. FIB-TEM technology was employed to characterize the microstructural evolution characteristics at the fatigue failure source area. Finally, considering the depth, area, and matrix hardness of the inclusions, a fatigue life prediction model based on gigacycle rolling contact fatigue (GRCF) was proposed. The prediction results closely matched the fatigue data of actual failed bearings.

Friction Modifier Performance in Twin-Disk Tests Using Disks of the Same Microstructure and Hardness

Friction management in the wheel-rail interface has received great attention from railway engineering in recent years, mainly due to the possibility of reducing wheel and rail wear. The addition of greases, lubricants and friction modifiers on the track has increased in the main railroads of the world. However, studies demonstrating the effect of applying friction modifiers are mainly carried out by manufacturers. To evaluate the action of the friction modifier, laboratory tests are less expensive tools and can give an indication of the benefit of the application. Thus, in this work, dry and wet twin-disk tests were carried out using disks with the same microstructure and hardness, evaluating only the action of the friction modifier. It was noted that the retentivity of the friction modifier had increased with the distance covered in the test. These results would contribute to increase the distance between applicators on the railway track and promoting a lower volume of product per distance traveled. The addition of a friction modifier also reduced the traction coefficient throughout the test, which contributed to lower wear of the disk. The friction modifier induced rolling contact fatigue cracks with greater depth and length due to hydro pressurization action. However, the addition was still beneficial because the wet condition keeping the friction at smaller values, the crack propagation takes longer to occur.

A novel multi-fidelity Gaussian process regression approach for defect characterization in motion-induced eddy current testing

This study introduces a novel framework aimed at addressing the challenge of surface defect characterization in lab-scale tests. It utilizes a high-speed rotational disc setup to simulate the dynamics of rolling contact fatigue found in railway inspections through Motion-Induced Eddy Current Testing (MIECT). A key component of our approach was the integration of experimental data and finite element modeling, aimed at interpreting the relationship between defect dimensions, velocity, and their impact on magnetic sensor outputs. Our research focused on two main objectives: developing a forward model to predict the differential peak-to-peak amplitude (ΔVpp) of sensor readings from defect size and velocity, and to perform inverse estimation of defect sizes from ΔVpp across continuous velocity ranges. The key findings reveal that for the forward problem, the Radial Basis Function Multi-Fidelity Scaling (RBF-MFS) method outperforms other multi-fidelity and single-fidelity approaches. Moreover, the proposed Gaussian Process Regression with Multi-Fidelity Scaling and Feature Discretization (GPR-MFS-FD) method outperformed the state-of-the-art multi-fidelity method in the inverse estimation of defect geometries. This innovative method leverages high-fidelity experimental data together with low-fidelity physics simulations via multi-fidelity scaling and feature discretization to effectively manage velocity range inputs, reflecting real-world operational uncertainties in high-speed transport vehicles and infrastructures. Our integrated and novel data-driven approaches advance defect characterization, enhancing MIECT's application in surface defect detection and analysis, with potential extensions to other NDE applications.

Wear of Cylinders in Tractive Rolling Contact and Implications for Modelling Back up Roll Wear in Steel Cold Rolling Mills

Wear of Cylinders in Tractive Rolling Contact and Implications for Modelling Back up Roll Wear in Steel Cold Rolling Mills

Advancing the understanding of short fatigue crack propagation: Leveraging ultrasonic testing device to approach rolling contact fatigue

This paper uses ultrasonic testing devices to approach the rolling contact fatigue (RCF) stress state experienced during rolling on an indented surface, in order to understand the primary cause of failures of rolling element bearings in aeronautics. It relies on testing specimens made of M50-VIM/VAR steel while inducing compressive preload. This leads to a localized multi-axial and non-proportional stress field, induced by an artificial surface defect created via electro-discharge machining (EDM). Observations reveal that the surface crack initiation occurs along the EDM beyond 108 cycles, with no shift observed from surface defects to sub-surface defects, as commonly seen in very high cycle fatigue (VHCF) regime. Our analysis suggests that the stress intensity factor range, ΔK, may govern surface initiation in the VHCF regime, particularly when the formation of fine granular area (FGA) is not feasible. Consequently, under fixed stress conditions, there exists a critical surface defect size below which short crack initiation becomes improbable. These results mirror the behavior usually observed for indentations and thereby connect ultrasonic loading with RCF. Besides, initiations of fatigue butterfly and FGA appear to be associated with VHCF tests, compression, high levels of multi-axial stresses, and the refinement of microstructure at low temperatures. These findings shed light on a potential link between fatigue butterfly and FGAs, attributed to the same underlying cause: cross-slip.

Research on the Wheel Wear and Rolling Contact Fatigue of Metro Vehicle Induced by Rail Corrugation

Rail corrugation is a common characteristic of track wear and exacerbates wheel–rail interaction and accelerates wheel wear and crack propagation. This study focuses on wheel wear and rolling contact fatigue of a metro vehicle under rail corrugation. Firstly, the characteristics of rail corrugation under service conditions are determined by statistical analysis of field data, and rail corrugation is applied to the established vehicle–track coupled dynamics model. Then, the wear index and the work of friction force as indicators of wheel wear are studied. Finally, based on the shakedown map and the criterion of maximum amplitude of shear stress, a simulation analysis of wheel rolling contact fatigue under rail corrugation is carried out. The results show that the increases in superficial fatigue index and accumulated fatigue are respectively 1.52 and 6.16 times in the wavelength range of 30 to 90 mm larger than those in the range of 90 to 210 mm. Furthermore, the cracks more easily occur 2 to 4 mm from the outer surface of wheel and expand along the wheel tread.

Rail rolling contact fatigue on a Chinese heavy haul line: Observations, monitoring and simulations

Severe rail rolling contact fatigue (RCF) occurring on curves of a heavy haul line in China was studied by field observations, monitoring tests, failure analyses and numerical simulations. Visual appearance, worn profiles, surface hardness, crack dimensions and so on were measured in field for rails and typical running wheels, meanwhile other related information was also collected. Significant influences of the radius of curvature and loaded/empty trains were figured out. RCF cracks on R600 m curves was found to get initiated in days, propagated downward very quickly in the first 2 months, and then stabilized at a depth of about 2.5 mm until rail replacement owing to further propagation into un-flowed bulk material. Though the failure analyses, crack depths measured by an eddy current detector were verified. Considering measured/collected data, a numerical approach combining a train dynamic model and the damage function model (Tγ) has been developed to predict the rail RCF occurrence, in which the influence of trapped liquids was better modelled by introducing a critical angle of the resultant creep force. Typical simulations showed that numerical predictions could well explain the observed phenomena, providing a useful tool for further studies.

Process of White Etching Cracks Formation in Carburized Bearing Steel under Rolling Contact Fatigue

Process of White Etching Cracks Formation in Carburized Bearing Steel under Rolling Contact Fatigue

Rolling Contact Fatigue Behaviors of 20CrNi2Mo Steel by a New Carbon and Nitrogen Composite Infiltration Process

ABSTRACTIn this paper, a new type of composite infiltration process was adopted for 20CrNi2Mo steel. Rolling contact fatigue (RCF) tests were carried out on the specimens treated with carburizing (C) and composite infiltration with carburizing and nitriding (C‐N). The results showed that after C and C‐N treatments were performed, the surface microhardness was increased by 78% and 114%, respectively, and the maximum CRS were −220 and −530 MPa. Moreover, the residual austenite volume fraction was controlled to approximately 10% for each treated sample. The fatigue limit of the C‐N sample was 11.3% higher than that of the C sample. The fatigue failure mechanisms are caused by the maximum shear stress distribution and surface roughness. The surface layer of the C‐N sample with higher hardness and more compressive residual stress inhibited the initiation of fatigue cracks, and the appropriate residual austenite in the carbon‐nitrogen infiltrated layer inhibited the propagation of fatigue cracks.

A Simplified Non‐Hertzian Wheel‐Rail Adhesion Model Under Interfacial Contaminations Considering Surface Roughness

ABSTRACTThe accuracy and efficiency of the wheel‐rail adhesion model are important to the wheel‐rail rolling contact issues. The purpose of this study is to develop a simplified non‐Hertzian wheel‐rail adhesion model under interfacial contaminations to predict the wheel‐rail adhesion coefficient. Firstly, a non‐Hertzian full elasto‐hydrodynamic lubrication (EHL) model was developed and applied to determine the wheel‐rail contact pressure and film thickness under interfacial contaminations. Then, the empirical formula of central film thickness available to non‐Hertzian wheel‐rail normal contact relating to train speeds, axle loads and material parameters were proposed based on a large number of non‐Hertzian full EHL simulation for smooth surface under interfacial contaminations using linear regression. The empirical non‐Hertzian central film thickness formula and minimum film thickness formula for wheel‐rail contact obtained in this paper show certain differences from the formulas based on Hertzian contact. Using the proposed non‐Hertzian central film thickness formula, a simplified non‐Hertzian wheel‐rail contact adhesion model was developed, and the adhesion coefficient was obtained at different speeds and compared with the field test data. The numerical results showed good agreement with field test data.

A novel prediction method for rolling contact fatigue damage of the pearlite rail materials based on shakedown limits and rough set theory with cloud model

Evaluation and prediction of wheel-rail rolling contact fatigue (RCF) damage can provide important theoretical guarantees for the service safety of wheels and rails and help make maintenance easier to plan. This study aims to develop a novel method for evaluating and predicting RCF damage of the pearlite rail materials with various initial shear yield strengths (ke). Based on the rough set mathematical theory incorporated within the cloud model of the comprehensive evaluation index (P0/ke*μt), a novel evaluation and prediction method for RCF damage states of various pearlite rail materials was constructed using the shakedown limits for pearlite rail materials with various initial shear yield strengths. To develop this novel prediction method, different evaluation indices for RCF damage states were designed. A comprehensive certainty approach was introduced to quantitatively analyze the actual measured values of distinct evaluation indices that corresponds to different RCF damage states, wherein the maximum value rule was applied. Moreover, the prediction results were confirmed after further verifying using the actual measured value of the P0/ke*μt. The results indicated that the predicted results were consistent with the test outcomes. The key feature of this prediction method was that it involved both the intrinsic shear yield strength of evaluated pearlite rail materials and wheel-rail rolling contact variables. On the basis of the two-dimensional classical shakedown map, a three-dimensional shakedown limit diagram for rail materials with varying initial shear yield strengths was further constructed using this novel prediction method. The three-dimensional shakedown limit diagram featured an inclined curved surface. As the initial shear yield strength of the pearlite rail materials increased, the curved surface tilted downward, indicating that an increase in the initial ke value of the pearlite rail materials could result in a lower shakedown limit.

Effects of rail hardness on transverse profile evolution and computed contact conditions in a full-scale wheel-rail test rig evaluation

This paper revisits a comprehensive data set generated in a prior test program using a full-scale wheel-rail test rig. The test program evaluated premium and standard grade rail steels with respect to wear and rolling contact fatigue (RCF). The current work evaluates the evolution of rail profiles throughout the test cases, taking advantage of the database of wheel and rail profiles that were collected. Contact conditions are modelled using the CONTACT library, including recent developments in the handling of conformal geometries and interfacial layers. Observations are made regarding the relative characteristics of rail profiles for each steel type, as they evolve with accumulated wheel passes, on the basis of the computed contact conditions.

Preparation of the sandwiched PS-SiO2-PVAc-SiO2 electrospinning fiber membrane with super-hydrophobic and self-cleaning and its performance in oil-water emulsion separation

Oil-water emulsion separation could improve the efficiency of oil resources and reduce environmental pollution. The efficiency of oil-water separation was directly affected by the surface hydrophobicity of the membrane and its reliability and reusability. Therefore, the construction of a reliable and reusable super-hydrophobic surface was very important. In this research, the EFM with sandwich structure of PS-SiO2-PVAc-SiO2 was easily fabricated by a three times liquid phase induction process and heat treatment. The PS-SiO2-PVAc-SiO2 EFM was first formed by a triple liquid phase induction process, then the EFM was heat-treated, the PVAc, which is a heat-sensitive material, resulting in SiO2 nanoparticles being welded onto PS fibers. The rolling contact angle experiment at an inclination of 8° proved that the PS-SiO2-PVAc-SiO2 EFM has super-hydrophobic properties. Meanwhile, the PS-SiO2-PVAc-SiO2 EFM showed excellent stability and reliability of super-hydrophobic properties after the EFM was washed or taped. In addition, the PS-SiO2-PVAc-SiO2 EFM had self-cleaning function and fine oil-water separation property. The oil-water separation efficiency was over 99.50 % and the flow rate was 68 L/m2h. After 5 times of oil-water separation, the flux and separation efficiency did not decrease significantly, which proved that the PS-SiO2-PVAc-SiO2 EFM could be reusable.

Rolling contact fatigue property of gradient rare earth addition M50 bearing steel with surface nano-grains and its inhibited martensite decay

A gradient nanostructured surface layer of ∼600 μm in thickness was prepared on M50 steel with rare earth additions by a surface mechanical rolling treatment. The initial microstructure was refined into nanosized grains (∼29 nm in diameter) in the top surface layer, causing a significant increase of surface hardness. Meanwhile, the grain size increases, and the microhardness decreases gradually to the matrix values with increasing depth. Rolling contact fatigue tests showed that the fatigue lives are significantly increased by the gradient nanostructured surface layer. Analysis of failure mechanism revealed that both softening in the near surface layer and hardening in the subsurface occur under rolling contact testing. And surface spalling is the predominant failure mode, of which the cracks initiate from primary carbides in the top surface layer owing to surface softening. In gradient nanostructured samples, the nano-grains inhibit carbon migration by impeding dislocation movement in the near surface layer, so that martensite decay is suppressed. Consequently, the crack initiation is inhibited, and the fatigue property is enhanced.

Peridynamic analysis of rolling contact fatigue crack propagation in rail welding joints with pore defects

Pore defects are prevalent in rail welding joints and significantly contribute to the propagation of fatigue cracks. This study develops a peridynamic (PD) model that incorporates the characteristics of pore defects to analyze their impact on rolling contact fatigue behavior. Initially, compact tension (CT) fatigue tests were performed to derive and validate the bond fatigue failure model specific to rail weld materials. Subsequently, pore defects were modeled as holes in the CT specimens, with experimental results being compared to PD simulation outcomes for validation. Finally, a wheel-rail contact PD model was constructed to investigate the mechanisms of fatigue crack propagation in rail welding joints affected by pore defects.

A new insight into the macroscopical cause of wheel rolling contact fatigue on Y25 wagons – axle box longitudinal guidance deviation

Wheel rolling contact fatigue (RCF) is a tricky issue for the railway industry. It is recently reported that the wheel RCF on Y25 bogies is more severe compared to other bogies with similar primary suspension structures. The axle box longitudinal guidance deviation (ALGD) could be a reason for the wheel RCF according to field observations. In this paper, a Y25 wagon dynamics model is firstly established and validated. The ALGD is modelled using non-linear force elements. The wheel damage function is used for RCF evaluation. Then, effects of ALGDs on force balances of wheelsets are preliminarily analysed in a quasi-static state. Four different scenarios for ALGDs are simulated and corresponding wear numbers are calculated. It proves that the wheelset lateral displacement, wheel‒rail contact forces, and RCF index will dramatically increase with the ALGD value. Potential wheel‒rail contact zones for the bogies with ALGDs are basically consisted with the recorded wheel RCF zones. Finally, maintenance suggestions are proposed according to the wheelbase deviation. The ALGD threshold should be 1.0 and 2.75 mm for the prevention on wheel RCF and wear, respectively. The results of this paper may provide a new insight into the macroscopical cause of wheel RCF on Y25 bogies.

Finite element analyses of rail head cracks: Predicting direction and rate of rolling contact fatigue crack growth

A numerical framework in 3D for predicting crack growth direction and rate in a rail head is presented. An inclined semi-circular surface-breaking gauge corner crack with frictionless crack faces is incorporated into a 60E1 rail model. The investigated load scenarios are wheel–rail contact, rail bending, thermal loading, and combinations of these. The crack growth direction is predicted using an accumulative vector crack tip displacement criterion, and Paris-type equations are employed to estimate crack growth rates. Results are evaluated along the crack front for varying crack radii and crack plane inclinations. Under the combined load cases and in the presence of tractive forces, the crack is generally predicted to go deeper into the rail than under pure contact. Crack growth rates for the combined load cases are higher than (but still close to) that for pure contact. A tractive force will increase growth rates for smaller cracks, whereas a steeper (45°) inclination will decrease the growth rate under the studied conditions as compared to a shallower (25°) inclination. Results should be of use for rail maintenance planning where deeper cracks require more machining efforts.

Hybrid finite element modeling of subsurface-originated spalling in flexible bearings with hoop stresses

The flexible bearing in a harmonic reducer undergoes structural deformation after being mounted on the cam, causing the bearing to operate under a complex stress state. A hybrid finite element model is developed to investigate crack initiation and propagation in flexible bearings with hoop stress under rolling contact fatigue loading. The model is coupled with continuum damage mechanics, and the damage evolution equation takes the maximum shear stress amplitude as the damage-causing stress since the hoop stress inevitably affects the fatigue life. The model is verified by comparison with the fatigue life of the inner ring without hoop stress. The crack initiation and spalling formation mechanisms in the inner ring assembled with the cam are analyzed in detail. Moreover, the effects of contact load and equivalent interference on the inner ring’s spalling morphology and fatigue life are studied.