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Computer modeling of processes of wear and accumulation of rolling contact fatigue damage in railway wheels using combined criterion
Abstract
An algorithm for computer modeling of the processes of wear and accumulation of the rolling contact fatigue (RCF) damage in railway vehicle wheels is introduced. The combined criterion of contact fatigue is obtained on the basis of the specific strain energy and of the criterion theories of strength. The proposed criterion is tested on the Hertzian problem with full sliding. RCF curve for wheel steel with a hardness 295 HB using proposed criterion is constructed by processing the results of the RCF tests of the wheel steel specimens. The example of modeling of the processes of wear and accumulation of RCF damage in the car wheel using combined criterion is given.
... Several researchers presented different methods to estimate the fatigue fracture plane [8][9][10][11]. Sakalo et al. [12] presented an algorithm for computer modeling of the processes of wear and accumulation of the rolling contact fatigue (RCF) damage in railway vehicle wheels. Seo et al. [13] evaluated residual stress of railway wheels' web plate by heat treatment due to the manufacturing process and changes of residual stress by braking using finite element (FE) analysis. ...
... (12) is obtained [57]. In order to obtain an accurate model for the cyclic loads state with variable range, Wheeler correction factor, is presented which is shown in Eq. (12) [58]: (12) According to Eq. (13), the value of this correction factor is strictly dependent on the radius of the plastic zone created at the crack tip. In this respect, the radius of the plastic zone at each loading is calculated according to the length of the various cracks, and the radius of the residual plastic zone after each loading, and is also n, the exponent obtained by experimental tests and laboratory observations. ...
In this paper, fatigue life and crack growth retardation of railway wheel specimens due to spectrum loading have been investigated. For this purpose, numerical and experimental methods are used to investigate the behavior of crack growth in the wheel specimens. The crack propagation is examined by using the stress intensity factor (SIF) values achieved from boundary element (BE) analyses. The non-linear Kujawski-Ellyin (KE) model has been adopted for the crack propagation under small-scale yielding (SSY) conditions. The periodic overloads have remained constant and the effect of overload ratio (OLR) and occurrence ratios (OCR) on the fatigue life has been investigated.
... However, the differences are less than 10%. UM is also validated for reliability by different previous studies (Qi et al., 2023;Kisilowski, 2021;Lu et al., 2020;Sakalo et al., 2019;Olshevskiy et al., 2015;Wang et al., 2021b;Xiao et al., 2017). ...
Train wheel wear significantly impacts wheel-rail interaction forces and is an unavoidable issue in the railway industry. This study focuses on regular wear, specifically changes in wheel profiles such as tread wear, flange height, and flange thickness. Effective wheel wear management is crucial for maintaining the reliability, safety, and efficiency of rail systems. However, regular measurement of wheel profiles is often limited by constraints such as dense traffic, budget, time, and remote assets, which reduces the effectiveness of traditional maintenance approaches. This study proposes a hybrid learning strategy combining supervised and reinforcement learning techniques to optimize train wheel wear management under these constraints and achieve predictive maintenance. The supervised learning model, developed from validated simulations, predicts wear progression, while reinforcement learning improves maintenance decision-making using basic operational data without regular measurements. Various machine-learning techniques are explored and fine-tuned to identify the best models for preventing faulty wheels without the need for frequent inspections. By integrating these two learning approaches, the framework enhances the accuracy of wear predictions and optimizes maintenance schedules, reducing the risk of over-maintenance or unexpected failures. This integrated model addresses challenges such as system complexity, limited data, and cost-effectiveness in the industry. In terms of supervised learning, the R² for tread wear prediction improves from 0.94 to 0.95 compared to previous studies, and the model, when integrated with reinforcement learning, significantly reduces defects based on wear and irregular wheel dimensions. This research is the first to integrate supervised and reinforcement learning specifically for train wheel wear management under limited measurement data constraints, offering a breakthrough compared to traditional methods that rely on regular inspections. The study provides significant benefits for the railway industry, including reduced maintenance costs, improved maintenance efficiency, lower defect rates, reduced possession and inspection time, and enhanced passenger comfort and safety.
... Several researchers presented different methods to estimate the fatigue fracture plane [8][9][10][11]. Sakalo et al. [12] presented an algorithm for computer modeling of the processes of wear and accumulation of the rolling contact fatigue (RCF) damage in railway vehicle wheels. Seo et al. [13] evaluated residual stress of railway wheels' web plate by heat treatment due to the manufacturing process and changes of residual stress by braking using finite element (FE) analysis. ...
In this paper, the fatigue life of pearlitic Grade 900A steel used in railway applications is investigated. To predict the fatigue life of pearlitic Grade 900A steel based on the number of cycles of the particular stress level in the load block, occurrence ratio and overload ratio, a feed-forward neural network is designed. The results of this artificial neural network are compared to the surface fitting method. Then sensitivity analysis is applied to the obtained artificial neural network values to measure the effect of each input parameter on the fatigue life. Finally, the genetic algorithm is applied to find the maximum fatigue life based on the input values.
... Therefore, in the past decades, reliability engineering has been recognized as a tool for developing and producing a product with the desired reliability and optimal design, and several tests have been developed in this field [8][9][10][11]. Sakalo et al. [12] presented an algorithm for computer modeling of the processes of wear and accumulation of the rolling contact fatigue (RCF) damage in the railway wheels. Seo et al. [13] evaluated residual stress of railway wheels' web plate by heat treatment due to the manufacturing process and changes of residual stress by braking using finite element analysis. ...
In this paper, the fatigue behavior of railway wheel specimens subjected to cyclic loading have been investigated via experimental tests and numerical analysis. The material behaviour of the wheel specimen has been modelled by means of the Ramberg‐Osgood equation. The non‐linear Kujawski‐Ellyin (KE) model has been adopted for the fatigue crack propagation under small‐scale yielding (SSY) conditions. The formulation of the rigid-insert crack closure (RICC) model has been applied to a specimen of railway wheel that has the same conditions as a real instance. The results indicate that the fatigue life of specimens decreases with any increase in load level.
... Both the experience 15,16 and laboratory experiments 17,18 showed the detrimental effect of such environmental factor on the fatigue life. The damage in condition of elastic shakedown (e.g., with no cyclic plastic strain) is usually approached in terms of multiaxial fatigue 19,20 or crack propagation. 21,22 The former approach considers fatigue strength an intrinsic material property, neglecting the effect of pre-existing cracks or defects; the latter presumes the pre-existence of a crack, which can propagate or not under the applied load. ...
A Failure Assessment Diagram (FAD), developed for rolling contact, was specifically formulated for railway wheel steels. The FAD allows combining a multiaxial fatigue criterion with the linear elastic fracture mechanics concept; in particular, it was used to assess the fatigue failure in wet contact, related to the pressurization of the fluid entrapped in surface cracks. The approach was applied to the results of previous bi‐disc tests carried out on three railway wheel steels, subjected first to a dry rolling‐sliding contact step, then to a wet contact step. The crack size distribution after the dry contact step was evaluated by a statistical approach; subsequently, the stress intensity factor during the wet contact step was estimated by finite elements. The results of the FAD agreed with the damage observed on the cross section of the specimens at the end of the tests. Furthermore, the FAD was used to determine the maximum allowable crack to prevent rolling contact fatigue, this way showing its potential as a damage tolerant approach.
... The surface and subsurface cracks can form RCF pittings and spalls [1,2], respectively. In the past few decades, many RCF models including empirical [3][4][5][6], numerical [7][8][9][10][11] and deterministic stress-based models [12] have been presented. Fatigue models for analyzing RCF are classified in two main groups: The first group predicts crack initiation utilizing the S-N and ε − N methods, and the other group predicts crack propagation based on fracture mechanics [13]. ...
In this paper, the rolling contact fatigue crack growth in the presence of multiple cracks and their interactions is studied. The proposed formulation is based on linear elastic fracture mechanics and singular integral equations. The body under the rolling contact is modeled by a half-plane weakened by a set of surface, subsurface and surface–subsurface cracks. Rolling contact is simulated by translational motion of an elliptically distributed force along the half-plane boundary. Several parameters, such as the distance between cracks, the value of initial crack lengths, the value of the friction coefficient, and the initial angle between cracks and the boundary of the half-plane are studied. Results obtained from this investigation are in good agreement in a special case with those reported in the literature. It is observed that in the system of two parallel surface and subsurface cracks with equal lengths, changing the distance between the cracks changes the growth paths, and when this distance increases to a critical value, the cracks grow independently. In addition, in the case of two parallel surface cracks when the left crack is shorter, the cracks have a stronger tendency to join together, which leads to pitting phenomena on the contact surface. Furthermore, in the system of two parallel subsurface cracks, it is seen that fast fracture occurs sooner when the initial angle of the cracks increases. In the system of parallel surface and subsurface cracks, the dominant failure mode is spalling.
Correlation analysis allows you to establish the presence of a linear relationship be-tween a change in one of the characteristics of a system and a change in another characteris-tic of the same system. Correlation studies are especially important for data analysis when the sample is limited. For railway metal products, the ability to predict fatigue crack growth characteristics and fatigue failure prediction is important because it is related to safety is-sues. Conducting long-term tests under multi-cyclic loading conditions is laborious and ex-pensive, and their implementation is not always possible in production conditionsAt the same time, the chemical composition and service mechanical properties of a batch of wheels are always known. The purpose of the work is to establish the influence of the main chemical components of carbon steel and mechanical characteristics determined during tensile, hard-ness, and impact tests on crack growth rates under cyclic loading conditions based on corre-lation analysis. According to the results of the analysis of the coefficients of the pairwise lin-ear correlation between the content of the main chemical elements in the steel and the fatigue crack growth indicators, a very high negative relationship Kth (the maximum value of the stress intensity coefficient, at which the crack does not develop during a given number of cy-cles) and Kfc (the stress intensity factor at which the specimen collapses, this value is achieved at maximum compression of plastic deformation and fracture by normal separation) with a change in carbon content, and for n (tangent of the slope of the straight line on the lin-ear, linear section of the kinetic diagram of fatigue fracture, which characterizes the rate of increase in the crack growth rate) – a high negative correlation with the change in the man-ganese content, K* (stress intensity coefficient at a crack growth rate of 10-7 m/cycle) – with the change in the vanadium content, but at the same time, a very high positive relationship was established between K* and the content of silicon and sulfur, with n – the content of phosphorus. The value of the Pearson coefficient was established at the level of 0.99 for such pairs of characteristics: Kth and elongation, Kth and impact strength, Kfc and shrinkage, K* and hardness, K* and ultimate strength) Criterion n is the least sensitive to changes in other mechanical properties, it is shown that only elongation and impact strength have a high cor-relation with this characteristic. Further research is needed to establish the relationship with the change in impurity elements and to establish functional patterns of the influence of char-acteristics on fatigue crack growth rates.
A review of modern simulation systems (technologies and programs) for rolling stock management, designed to train students of transport universities and employees of Russian Railways, was carried out. A cross-platform simulator has been developed based on the use of an application creation platform and interactive content. The 2D RailWay Simulator cross-platform simulator is designed to optimize the educational process, which allows you to assess the level of training of students both in preparation for the exam and as the final certification of students by profession as an assistant driver of an electric locomotive. The simulator can be adapted when studying the controls of the electric locomotive in the discipline “Rolling stock of railways” for the specialty 23.05.03 Rolling stock of railways of all forms of training. The simulator creates the effect of presence in a real locomotive by displaying the track situation of locomotive cabins and control panels, as well as safety devices and auto-driving systems based on 3D graphics. This complex is developed on the basis of updated design documentation and original algorithms for rolling stock management. The functionality of the cross-platform application is based on a special modeling environment and a system of mathematical models of devices used on locomotives and motor car rolling stock. A methodology for training students on a cross-platform simulator has been developed.KeywordsRailway simulatorEducational standardEducational processCompetenceApprobationSimulatorSpecialty
This study presents the results of modelling the rolling contact of the elastic sphere and the elastic half-space in the presence of a thin intermediate viscoelastic layer which properties are described by an elastic nonlinear Winkler body in the normal direction and a viscoelastic Maxwell body in the tangential direction. The analytical–numerical approach for the estimation of contact fatigue damage, accumulated in the elastic half-space under rolling friction conditions, is developed. The proposed model can be used, in particular, to study the effect of mechanical properties of the friction modifiers (elastic moduli and relaxation times) and its thickness as well as the relative slippage on the formation of the surface and under surface contact fatigue cracks in rails. The results of the analysis can also be applied for the estimation of efficiency of solid lubricants in rolling contacts under given operating conditions.
This work is devoted to researching the influence of assembly stresses in a rail joint on its stress condition. A finite element model is prepared, consisting of a rail part and a fish plate, fastened with bolts. The model fully takes into account the geometry of the joint assemblies, its rigidity characteristics and the contact interaction between the rail and the fish plate. The rail rests on elastic supports that simulate the rigidity of the rail base, which includes rubber plates, sleepers, and ballast. For the solution, the finite element method and the DSMFem software package are used, which allows introducing logical contact finite elements in the contact area of the rail and the fish plate. The results of calculating contact pressures and stresses in the rail in the process of their assembling into a single rail length are presented. Comparing the calculation results with the approximate data obtained by the known methods is carried out.
The contact fatigue phenomenon in conditions of cyclic sliding or rolling is studied based on the model of contact fatigue damage accumulation in the subsurface layers of the material. It is assumed that the rate of the damage accumulation depends on the principal shear stress amplitudes. The results of numerical modelling show that the contact fatigue fracture process in the conditions of a constant load, acting on the sliding or rolling body, consists of the following stages: the incubation period, the running-in period with the alternating detachment of material’s fragments of certain thickness (the mechanism of delamination) and the surface wear, and then the steady-state stage, characterizing by the surface wear with a constant rate. The influence of the sliding friction coefficient, the relative slippage and the strength properties of contacting bodies on the evolution of the accumulated damage in the surface layers and on the fatigue wear kinetics in sliding and rolling contacts has been analyzed.
The contact problem for a rolling elastic sphere and an elastic half-space covered with a viscoelastic layer (third body) is considered. The layer properties in normal and tangential directions are described by the Maxwell model. Based on the macroscopic approach of the contact fatigue damage accumulation the rate of damage accumulation in an elastic half-space is assumed depending on the amplitude values of the principal shear stresses or the equivalent von Mises stress. The influence of the relative longitudinal slippage, the sliding friction coefficient and the properties of the intermediate layer on the internal stresses and at the depth of contact fatigue cracks initiation is studied. The results indicate that the maximum damage can occur both on the surface of the elastic half-space and at a certain depth. The increase of the friction coefficient or relative longitudinal slippage leads to reaching the maximum value of the principal shear stress amplitude on the surface of the half-space, which results in contact fatigue surface fracture (wear). The results also demonstrate that the presence of a viscoelastic layer leads to a decrease of the principal shear stress amplitude within the elastic half-space.
Fatigue wear and damage accumulation take place in the wheel and rail interaction, rolling bearings and so on. In this study the three-dimensional contact problem for a cyclic rolling of an elastic sphere over an elastic half-space is considered which allows us to study the effect of relative slip velocity on the damage accumulation and kinetics of fatigue wear. The contact region consists of a stick and slip subregions, which configuration is unknown in advance. The relation between normal and shear stresses in the slip subregions is described by the Coulomb law. It is assumed that the rolling body and the base have the same elastic properties, and the Hertz solution is used to calculate the normal stress distribution in contact region. Determination of the shear stress is based on the variational method. The results show that the wear process consists of the incubation stage and then the detachment of the layers of definite thickness takes place. The thickness of the detached layers decreases with time. The influence of the relative slip velocity, sliding friction coefficient in contact region and parameters of the damage accumulation function on the fatigue wear process was also studied. The developed model can be used to predict the fatigue wear features in rolling contact of elastic bodies.
The article describes a developed laboratory setup for studying vibrations in the “wheel-railway track” system. With its use, the rigidity of the ballast layer and the vibration damping coefficient is determined. A dry friction model can be applied in the experiment, where railway ballast is a free-flowing medium. In the calculations, it is replaced by a model of a viscous friction medium, so this model provides equivalent energy dissipation in the ballast layer. Identification of the vibration damping coefficient was carried out by comparing the oscillation waveforms obtained experimentally and using a computer model of the setup. The suggested scheme of a laboratory setup for determining the elastic and dissipative characteristics of the ballast layer provides conditions for applying a load to the ballast layer close to real (full-scale) conditions. The obtained values of the vibration damping coefficient and the stiffness of the ballast layer fall into the corresponding ranges given in the literature for various states of the ballast layer.
Railway transportation system is one of the main needs of the population living in industrialized countries. Many studies have been conducted by engineers due to the importance of railway wheels and railways as a major part of the train. But due to progress in railway technology, in recent years a new type of train wheel known as rim-wheels is presented that their fracture is investigated in this study. The goal of the present study is to calculate stress intensity factors numerically using the boundary element method in railway wheels based on experimental data of material behavior. For this purpose, a series of experiments were performed to determine the behavior of the railway wheel material as well as the data required for numerical analysis. The innovation of this research is that the stress intensity factor is calculated resulting from residual stress of press-fit and heat-treatment processes. Then, the stress intensity factors resulting from the two processes are superimposed in pure mode I, mode II, and mode III loading due to the same crack geometries. Also, the study includes a survey on the effect of crack length on crack propagation as one of its main effective factors. Besides, fatigue crack growth path is calculated and its propagation is also estimated and the effect of different parameters is studied on fatigue crack growth and path.
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.
Rolling contact fatigue of an urban railway wheel was analysed during its rolling FEM analysis was performed using 3D modelling of rail and wheel, in which the slope of the rail and nonlinear isotropic and kinematic hardening behavior of the rail and the wheel were considered. The maximum von Mises stress and contact pressure between the rail and wheel were determined under an axial load of 85 kN. The contact pressure distributions calculated using elastic Hertz theory and three-dimensional elastic-plastic stress analysis are compared. The maximum contact pressure of the wheel from the elasticplastic FE method is slightly lower than the value from Hertz contact theory with elastic deformation. The rolling contact fatigue (RCF) of the wheel due to rolling contact was determined tobe infinite by Dang Van criterion.
Computer models of freight cars with three-piece and Y25 bogies are considered and compared. Efficient numeric methods for
simulation of vehicle models in the presence of frictional contacts are discussed. Some simulation results on derailment safety
analysis and influence of track gauge value on freight-car dynamics are presented. Methods of stress loading and durability
analysis based on computer simulation and some results are presented. A tribodynamic model of railway vehicle-track interaction
and results of computation of wheel and rail profile wear are discussed.
This article investigates the variables that influence the fatigue limit of bearing steels. The experimental evaluation of the fatigue limit of rolling element bearings is a difficult, time consuming and an expensive process. Hence, an analytical method is desirable. Modern bearing steels have a complex microstructure with various non-metallic inclusions, which act as local stress risers and may cause the matrix to accumulate micro-plastic strain. This eventually results in the nucleation of fatigue micro-cracks and ultimately bearing failure. Therefore, one interpretation of the fatigue limit is as a macro-scale stress below which no local yielding occurs. Such a fatigue limit will be dependent upon the mechanical properties of both the matrix and the inclusions as well as the inclusion geometry and distribution. A finite element analysis (FEA) based study was conducted to determine the critical factors that have the largest impact on the fatigue limit of bearing steels during rolling contact fatigue. The effects considered include static vs rolling contact, inclusion geometry (size, shape, orientation, and distribution), the temperature dependence of the mechanical properties of both the matrix and the inclusion (elastic modulus, thermal expansion coefficient, and yield strength), and the possibility of an inclusion becoming debonded from the matrix. The results of this study showed that a static contact model instead of rolling contact model is sufficient to capture the fatigue limit in the case of hard, stiff inclusions. The stress concentration due to debonded inclusions was much more dramatic than any of the other terms considered followed by the change in the elastic modulus due to temperature. The effect of the geometry (size, shape, and orientation) of an individual stiff inclusion on the fatigue limit was found to be relatively minor.
An algorithm for computer modelling of the process of accumulation of rolling contact fatigue (RCF) damage in railway vehicle wheels is introduced. The amplitude of maximum shear stress is adopted as a criterion for fatigue failure during rolling. RCF curves for wheel steels with a hardness 255–330 HB are obtained by processing the results of the RCF tests of the wheel steel specimens. Effect of the wheel steel hardness on accumulation of the RCF damage is investigated.
The paper presents the results of experimental and numerical investigations on regular wear of wheel profiles. Experimental tests were performed on a full-scale roller rig and allowed to measure the evolution of wheel profiles as well as contact forces and several quantities describing the motion of the wheelset. As to the numerical investigations, a wear prediction model was developed, based on the interfacing of a multi-body simulation code for rail vehicle dynamics, of a local contact analysis model and of a material wear model that assumes a proportionality relationship between wear and frictional power. The validation of this model by comparisons with the measurement performed on the roller rig is still in progress. Some preliminary results are shown in this paper.
The fatigue life of wheel treads has a strong bearing on the economy and safety of rail transportation. An understanding of fatigue mechanisms and a prediction of lifetimes are of interest to both manufacturers and operators. The issue addressed in this paper is how to design a suitable mathematical model for fatigue life prediction for railway wheels. In the past, several models have been developed for the analysis of multiaxial fatigue in general and for the study of rolling contact fatigue in particular [1]. However, due to the complexity of the problem, there is still no "standard model" available for prediction of the lifetime of a railway wheel subject to high cycle rolling contact fatigue. The aim of the model to be presented and discussed in the following is that it should serve as a fast and sufficiently accurate tool in the practical study of rolling contact fatigue. To this end, a semi-analytical approach and an equivalent stress criterion are employed. The problem of how to select an appropriate equivalent stress criterion is treated in some detail. Some calculated results are compared to statistical data obtained for passenger trains from workshops doing wheel reprofiling. Finally, the influence of some parameters on the predicted damage and lifetime is studied.
The wear of a wide range of material combinations has been studied in unlubricated conditions. Loads of 50 g to 10 Kg and speeds of 2 to 660 cm/s have been used. A representative selection of the results is given. As a broad classification two contrasting mechanisms of wear have been observed. In nearly all experiments, and for all types of wear mechanism, once equilibrium surface conditions are established the wear rate is independent of the apparent area of contact. The wear rate is accurately proportional to the load for only a limited number of combinations but there are many other examples for which the relation between wear rate and load shows only a small deviation from direct proportionality. It is suggested that with the same surface conditions the wear rate is proportional to the load; in practice this simple relation is modified because the surface conditions depend on the load. These rules of wear may be derived, on a priori grounds, from the experimental results, or from more detailed theoretical calculations.
An algorithm “Fastsim” for the simplified theory of rolling contact is described which is 15-25 times as fast as the existing programs Simrol (Kalker), and 3 times as fast as Rolcon (Knothe). The relative total force computed with Fastsim differs at most 0.2 from that calculated with Simrol, Simcona (Goree & Law), Rolcon, and the “exact” program Duvorol (Kalker). Descriptions and lists of an Algol 60, and HP 67 program version are available upon request: the Fortran IV version is given in the paper.
Recently, various methods have been proposed to assess the risk of rolling contact fatigue failure and in particular, the Dang Van multiaxial fatigue criterion has been suggested in a simple approximate formulation by Ekberg, Kabo and Andersson. In a recent note by Ciavarella and Maitournam, it was found that the approximation is only valid in a restricted range of cases. Here, a much larger range of conditions including elliptical contact and partial slip conditions are considered and analytical formulae are also derived. The Ekberg, Kabo and Andersson calculation is shown to be a good approximation only for nearly circular contacts, high Poisson's ratio and high Dang Van constant. The Dang Van fatigue limits are very high, particularly for line contact: however, under those conditions ratcheting deformations also are likely to occur unless perhaps for very hard materials showing cyclic yield limit much higher than fatigue limit (these materials in turn could then show very low wear and be prone to fatigue crack propagation). Classical findings about the RCF fatigue suggest nearly twice higher fatigue limit in point contact with respect to line contact conditions, and this is apparently in contradiction to the Dang Van criterion. A possible qualitative explanation is that in point contact above elastic shakedown there is a regime of cyclic plasticity, rather than the direct transition to ratcheting regime as in line contact. However, the Dang Van criterion has been found to be possibly too conservative under RCF also by other authors recently, and further investigations are required.
Three types of rolling contact fatigue of railway wheels are prevalent for freight cars of the Russian Railways: wheel spalling, shelling and thread checking. Though all these defects and mechanisms of their formation are generally known, however, there are many particularities in the defect's appearance, formation and development that should be studied. Results of theoretic studies and modeling of the defect formation are presented and discussed. As creep and associated forces are considered as one of the most damaging mechanism for the wheel–rail interface, particular attention is given to study the influence of creep velocities and the coefficient of friction on the contact stress distribution.
This study is aimed at the deterioration of rolling contact fatigue (RCF) life of pearlitic rail steel, under rolling-sliding conditions, where the wet phase of the test is preceded by different numbers of dry cycles. It is shown that initial dry cycles above a critical number causes sudden and significant deterioration in RCF life. This effect has been explained using the argument of plastic strain accumulation (ratchetting) in the surface layer during the dry phase when the coefficient of friction is above 0.25. A strong correlation was found between the degree of ratchetting and the deterioration in RCF life. An empirical relationship to estimate this deterioration was concluded.
A re-interpretation of recent RCF experiments by Clayton and Su (C&S) [Wear 200 (1996) 63] under water lubricated rolling/sliding conditions, with careful measurements of ratchetting strains, and their comparisons with experimentally observed lives, seems to confirm the validity of ratchetting failure (RF) mechanism and Kapoor’s “critical ratchet strain” as a material property. However, the complexity of modelling the ratchetting phenomenon and the uncertainties on the material’s critical ratchet strain, suggests that perhaps a more realistic alternative is the use of empirical Wöhler-like life curves similarly to currently used for the contact fatigue evaluation in gears design and standards. In particular, it is found that the “pitting” fatigue limit at 107 cycles suggested by the gears standard is reasonably accurate also for the C&S experiments on various typical rail steels. Since the gears life factor suggested for gears turns out quite conservative at shorter lives, it seems a single new life factor could be suggested, at least for all pearlitic and bainitic steels tested by C&S under water lubrication.
The rolling contact fatigue behavior of steels that are, or could be, used for railroad rails is reviewed. Laboratory tests that reproduce the type of cracks observed in service rails have been employed to study the effects of maximum Hertzian contact pressure and slide/roll ratio on fatigue performance under water lubricated conditions. A comparison has been made of pearlitic and low/medium carbon, carbide free, bainitic steels. The development of ratchetting strains has been investigated and an empirical model produced.
Ratchetting strain measurements of a pearlitic steel in rolling/sliding contact have been made at a number of contact pressures. Ratchetting strain was a non-linear function of contact pressure and the number of contact cycles. The most important feature of the non-linearity is the asymptotic way in which the strain rate gradually decreases to reach near saturation over a significant portion of the total rolling contact fatigue life. The experimental data suggest that two parameters, an initial strain increment and strain rate, are needed to describe ratchetting behavior. A critical strain to crack initiation in likely to be an additional controlling factor for surface-initiated rolling contact fatigue dominated by shear band cracking.
Evolution of the simulation study of a railway wheel profile trough wear
- Chudzikiewicz
New particulars of wear of heavy railway carriage wheels
- Specht
Identification of the wheel-profile wear-coefficients in the framework of the simplified-combined wear hypothesis
- Szabo
On rolling contact fatigue analysis practice in railway industry: models and applications
- Nast
Numerical method for solving the contact problems for the solid bodies using the finite element fragments on the elastic foundation
- Sakalo