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• Verified frog crack growth model combines impact simulation and fracture analysis. • Crack location and angle are more influential than train speed and axle load. • Observed accelerated growth of transverse cracks near the frog nose. • Proposed inspection strategy based on crack type, cumulative tonnage, and headway. Fatigue cracking is one of the notable failure mechanisms of railway turnout frogs due to high contact forces induced by the wheel-rail impact. However, the treatments specific to the frogs of cast high manganese steel to prevent sudden failure are rarely provided and are independent of the crack conditions, which can significantly affect the fatigue crack growth rate. To address this shortcoming, the fatigue crack growth in a cast high manganese steel frog is computationally investigated with varied wheel and crack conditions. The dynamic wheel-frog impact is first simulated to obtain the distribution of contact pressure imposed on the frog, and the propagation of the fatigue crack is then predicted using the finite element formulation in fracture mechanics. The simulation results show that the train speed and axle load can change the maximum contact stress. Nevertheless, when representing the growth rate in terms of the cumulative passing axle load, the effect of axle load and train speed on the crack growth is minimal and moderate, respectively. In contrast, the initial crack conditions, including the location and angle, have an overweighted influence. As a result, an inspection scheduling strategy for identified cracks with different conditions is proposed to consider both safety and operational efficiency. [ABSTRACT FROM AUTHOR]

• Three dynamic indicators for predicting plastic flow in railway systems based on the mechanics of wheel-rail contact, Tresca's yielding criterion and shakedown theory. • A dynamic method that is simple to model and fast to compute for predicting plastic flow in railway systems. • Key parameters affecting plastic flow and rolling contact fatigue. • A dynamic approach for the impact of plastic flow on rolling contact fatigue damage. • Effect of different degrees of plastic flow on rolling contact fatigue. 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. [ABSTRACT FROM AUTHOR]

• Typical factors affecting the wheel-rail dynamic response are comprehensively considered to reveal the short-term load characteristics of frog under complex conditions. Meanwhile, based on the ellipsoidal Gaussian extrapolation theory, long-term wheel-rail load characteristics are obtained. • Combined with the strain energy fatigue parameter theory, a prediction method for the fatigue life of nose rail under complex conditions based on load spectrum preparation was proposed. • The location between the 30 mm and 35 mm sections of the nose rail has the shortest rolling contact fatigue crack initiation life and should be focused on during damage inspection. The rail profile irregular variation and wheel-rail relationships complexity at the gap in the frog enhance the wheel-rail impact forces, frequently resulting in rolling fatigue damage under complex cyclic loads. Therefore, it is particularly important to study the transient rolling contact load characteristics of fixed frog and to compile load spectrum considering various complex conditions for analyzing the fatigue damage of frog and extending the service life of structure. In this paper, a 3D transient FE model of wheelset and fixed frog is established, revealing rolling contact behavior of wheel-rail in frog area from both macro and mesoscopic perspectives. In order to investigate long-term load characteristics of wheel and rail under complex service conditions, the changes of line conditions, load conditions, rail wear state and other influencing factors in actual operation are taken into account. Based on elliptic Gaussian kernel density theory, a method for compiling the load spectrum of fixed frog nose rail is proposed, and the FP method is used for fatigue crack initiation life prediction of nose rail in fixed frog. The results show that the force state is more severe when passing through the frog in straight reverse direction, and resonance is prone to occur in the third and fifth vertical bending modes of the frog, as well as the fourth and sixth vertical bending modes of the stock rail. The increase in factors such as speed, axle load, wheelset lateral displacement towards frog side and wing rail wear will exacerbate wheel-rail impact and shorten frog service life. Different factors have an impact on the overall amplitude, oscillation center range, and maximum frequency load of the wheel-rail force in the long-term load spectrum of the frog. The fatigue crack initiation area of nose rail is mainly in 30 mm–35 mm sections, which is consistent with the on-site flaw detection results, verifying the accuracy of the calculation method developed in this paper. [ABSTRACT FROM AUTHOR]

• First S-N curve of surface initiated damage under rolling contact fatigue. • Uniquely conservative mechanical fatigue failure definition used for surface damage. • RCF and torsional fatigue S-N curves have similar fatigue strength exponent. • Study unveils that torsion tests can predict RCF surface damage results 10x faster. • Different operating regimes identified based on RCF surface damage severity. This paper presents fundamental findings on equivalence of rolling contact fatigue (RCF) driven surface damage and torsional fatigue modes of failure. Fatigue experiments were conducted for both modes of failure using AISI 4130 case carburized steel specimens. A Thrust Bearing Surface Pitting Rig (TBSPR) was designed and developed to perform RCF tests on flat test specimens using thrust ball bearings. The experiments were conducted in boundary lubrication regime, simulating the contact conditions in tribological machine components. The current investigation presents a novel approach where the effect of contact pressure and number of fatigue cycles on the initiation of surface damage was characterized by surface profilometry of the wear track after each test to generate a stress-life (S-N) map. The S-N map provides unique insights to early detection of RCF driven fatigue damage. The S-N map was utilized to generate the surface damage S-N curve. Torsional fatigue experiments were conducted on the same material, and the S-N curves of both failure modes were compared. The comparison shows key similarities between the two S-N curves, as they differ by a simple scaling factor. This investigation demonstrates that RCF driven surface damage characteristics can be predicted by conducting much simpler, and faster, torsion fatigue tests. This paper also presents a novel methodology to determine contact pressures to avoid incipient micropitting/microdenting damage. [Display omitted] [ABSTRACT FROM AUTHOR]

• The model can account for the non-linear lifting of the flange groove and the effects of wheelset traverse and side roll. • The wheel tread and flange are alternately loaded with two wheel load transition areas in the frog area. • Wear in the flange bearing area is significantly higher than in the tread bearing area, with an increase of 59.7%. • RCF damage dominates in the wing rail and the two wheelload transition areas. • Reducing the speed to 15 km/h significantly improves the service performance of the fixed frog. The tram No. 3 turnout fixed frog uses a variation in the depth of the flange groove so that the wheel rolls over the frog area in a continuous flange bearing. This method of travelling over the turnout requires the wheel load to transition back and forth between the tread and the flange, resulting in wheel-rail impact, which in turn affects service life. In order to investigate its service characteristics, this paper has established a transient wheel-rail rolling contact finite element model for the No. 3 turnout fixed frog. The macroscopic dynamic response and microscopic wheel-rail contact solution as the tram passes through the turnout at different axle weights and speeds are analysed in detail, and the changing patterns of wear and fatigue damage are investigated. The research shows that rail wear is particularly severe in the wheel flange bearing area, approximately 1.6 times greater than in the tread bearing area. In addition, when tram speeds are reduced to 15 km/h, there is a significant reduction in wheel-rail impact and wear, thereby improving ride smoothness and safety. The results of this study are of great significance to the operation and maintenance of the No.3 fixed frog turnout. [ABSTRACT FROM AUTHOR]

[Display omitted] Material microstructure plays a key role in crack initiation under rolling contact fatigue. When studying microstructure with crystal plasticity finite element method (CPFE), mesh sensitivity study is of great importance, as the surface-near region is under high uniaxial stresses. In this paper, a new structured mesh strategy is purposed and compared with the classical unstructured mesh strategy. Modelling tests on a bi-grain and a polycrystal model show the calculation of geometrically necessary dislocation (GND) density, recently proposed as a suitable fatigue damage indicator, is highly dependent on mesh morphology, when GND hotspots tend to appear near distorted elements even in homogeneous materials. With uniform mesh size and shape, structured mesh elements can provide physically more acceptable GND calculations, which is particularly important in loading scenarios with complex stresses, such as rolling contact fatigue. Computational efficiency is also improved compared to unstructured models because a smaller number of elements are required in a structured mesh model and pre-processing of the mesh is not required. [ABSTRACT FROM AUTHOR]

Abstract Due to the improvement of the wear property, rolling contact fatigue including shattered rim and shelling are the main failure causes of the high-speed railway wheels. In this paper, shattered rim and shelling occurred on the service wheels of the China Railway High-speed (CRH) trains were systematically investigated. The recorded data of the last ten years CRH operation indicated that all shattered rims and shelling were detected with serving >106 km (corresponding to the fatigue life 107–109 cycles) which is very-high-cycle fatigue (VHCF). The crack initiation region of shattered rim located at the depth of 10–25 mm from the tread, while that of shelling located at the depth <10 mm from the tread. The VHCF features under rolling contact loading were observed on the opening crack surfaces, i.e., similar VHCF features in uniaxial loading including the defect, fish-eye, and crack propagation region and unique VHCF features of the three dimensional crack surface feature, beach bands uniformly distributed in the crack propagation region, absence of fine granular area (FGA). The VHCF model considering the stress distribution, defect size and hardness were applied to discuss the failure mechanism of the shattered rim and shelling. Highlights • The shattered rim and shelling are caused by very-high-cycle fatigue (VHCF) under rolling contact loading. • Unique features were presented in the crack initiation region of VHCF under rolling contact loading. • The multi-axial stress distribution, the large defect, the hardness distribution are responsible for the VHCF behavior. [ABSTRACT FROM AUTHOR]

• A first study of the effect of full creepage on RCF crack growth behaviour. • Predicted crack growth directions show a good agreement with field observation. • Lateral and spin creepages can significantly affect K II and K III evolutions. • Increase in spin creepage is more detrimental to RCF crack driving force. In heavy-haul railway systems, the experience of high traction force of rails in curved tracks significantly accelerates the rolling contact fatigue crack growth. The overall level of traction force and its detailed distribution within a contact patch can be determined by the extent of wheel slips in different directions, also referred to as creepage. However, few studies have focused on quantifying the influence of creepage on rolling contact fatigue crack growth behaviour. In this paper, a numerical method is proposed to investigate the non-proportional mixed-mode rolling contact fatigue crack growth behaviour in the presence of severe longitudinal, lateral and spin creepages. To partially validate the proposed numerical method, the predicted crack growth directions on the rail surface are compared with the cracking patterns obtained from field observations. A parametric study is also conducted to further quantify the influence of different creepage combinations on the evolution of stress intensity factors at the crack front. Results show that both lateral and spin creepages can significantly affect the phase and maximum magnitude of K II and K III during one complete loading cycle. Moreover, the increase of spin creepage is found to have a more detrimental effect on overall RCF crack driving force than the increase of the other two creepage components. [ABSTRACT FROM AUTHOR]

Railway crossing usually bears enormous impact force and rolling contact stress during service, resulting in various surface defects or even failure of the wing rail. Laser cladding (LC) maraging-steel coatings on the rail surface shows great potential for hardfacing or repairing the wing rail effectively. However, the performance of as-deposited coatings can hardly meet our expectations because the in-situ aging heat treatment (IAHT) effect during LC is too weak to trigger the precipitation effectively. In this paper, the LC technology assisted with in-situ induction heating (LC-IH) was proposed to prepare high-performance 18Ni300 coatings on the surface of bainitic wing rail, so as to make the precipitation much more sufficient. As a result, the bending strength and impact toughness of bainitic wing rail deposited with 18Ni300 coating by LC-IH are enhanced by 4.2% and 20.0%. Meanwhile, the wear resistance of the LC-IHed rail is enhanced to 3.3 times and 1.3 times as much as those of the untreated rail and LCed rail, respectively, while its plastic deformation and fatigue crack propagation depths are greatly decreased. The main mechanism is that the cumulative IAHT time during LC-IH process was prolonged by 15.8 times as much as that during LC process, making the nanoprecipitates precipitate much more effectively. Therefore, the LC-IH technology can prepare high-performance coatings in-situ without bulk heat treatment in the furnace, showing strong industrial potentials in the future. [ABSTRACT FROM AUTHOR]

• A two-stage simulation strategy was proposed to investigate the mechanisms of RCF cracks on the rail, consisting of a dynamic FEM for wheel and rail interaction and a coupled static FEM/BEM for crack growth. • The critical wheel positions for crack propagation during wheel approaching to and departing from the crack were determined and correlated with the different cracking mechanisms. • The orientation of the crack in rail played an essential role in crack growth behaviors. 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. [ABSTRACT FROM AUTHOR]

• FASTSIM algorithm implementation in Abaqus to consider slipping and adhesion zones of the wheel/rail contact patch. • XFEM rolling contact fatigue (RCF) analysis of a 60E1 rail profile considering creepages. • Validation of the developed rail model with data available in the literature. • Sensitivity analysis to determine the influence of contact conditions on the fatigue life of rails. 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

• Welding residual stress distributions in rail head and web are different; • Residual stress affects the rail subsurface crack propagation path, life and rate; • The shear stress in different directions made the crack propagation paths different. To accurately evaluate the influence of welding residual stress on the fatigue crack propagation behavior of rail, the distribution of residual stress of welded rail was predicted, the subsurface fatigue crack propagation type, path, rate and lifetime of the rail and the welded rail with residual stress were calculated and compared. The results showed that the subsurface crack propagated with II + III mixed-mode and the slip propagation of mode II was dominant for both the cases of residual stress existing and not, while the crack propagation path, rate and lifetime were quite different for the two cases. For horizontal circular cracks, when there was no welding residual stress, the crack propagation path was mainly transverse under wheel-rail contact load, the propagation rate was relatively small, and the propagation lifetime was longer. When there was welding residual stress, the crack propagated longitudinally, the crack propagation rate increased significantly, and the fatigue lifetime was shorter. [ABSTRACT FROM AUTHOR]

• A unique pin-loaded SENT specimen was fabricated using electron-beam welding for fracture testing of thin-walled pipe. • The η CMOD -factor, or crack mouth Eta-factor, significantly differed from literature solutions for pin-loaded SENT specimens. • The experimental J-error was estimated to be < 5% for the present analysis η CMOD and 10–30% for literature values of η CMOD. • The crack growth correction is best derived using the Eta-factor computed at the pin, even when J is calculated using η CMOD. • Friction at the pin-specimen contact reduces the stress intensity geometry factor, F , and η CMOD and increases experimental J-error. There is considerable interest in the fracture community for representative measurements of the resistance of pipe structures to fatigue crack propagation and fracture. However, to date there has been a lack of standard test methods available for the accurate fracture testing of radially propagating longitudinal flaws in thin-walled piping. A pin-loaded single edge-notched tensile (SENT) specimen was developed, denoted the CSR SENT specimen. This test geometry has been shown to reproduce the plastic constraint for longitudinal cracks in thin-walled piping, resulting in transferable fracture test data to that application beyond the conventional limits of single-parameter J-dominated fracture mechanics. The CSR SENT was simulated with finite element analysis (FEA) to yield the parameters necessary for the experimental determination of the J-integral using standard fracture test methods. The FEA results showed that the stress intensity geometry factor, F , for the CSR SENT matched literature solutions for most crack lengths, but that the CMOD-Eta factor – η CMOD , used to calculate the plastic component of the J-integral from the applied load and crack mouth opening displacement (CMOD) – differed from literature solutions and is specimen size-dependent. The error associated with the calculation of the J-integral is estimated to be < 5% with the obtained η CMOD , while the use of literature solutions for η CMOD result in significant non-conservative overestimates of the experimental J-integral. It is recommended that fracture testing be limited to a specific specimen geometry associated with a FEA-derived η CMOD solution. The crack growth correction to the J-integral measurement was also obtained, and is recommended to be derived from the η pin (also referred to as η LLD, derived from the load-displacement of the pin boundary), which can be used alongside the η CMOD for experimental calculation of the J-integral in standard single-specimen fracture testing. Friction at the pin-specimen interface results in significant non-conservative bias error in the J-integral, and a rolling pin-clevis contact is recommended with a pin diameter twice that of the specimen width to mitigate pin contact plasticity and damage. [ABSTRACT FROM AUTHOR]

This paper aims to propose a new and fast method to estimate the multiaxial non-proportional elastic–plastic stress and strain time histories developed in rails due to rolling contact and evaluate its accuracy for fatigue analysis. The method has the pseudo-elastic stress time history as input, which is obtained by a coupled analytical and numerical method. Therefore, a method originally proposed for notch-root elastic–plastic stress–strain analysis was extended to the Rolling Contact Problem (RCF). The problem is solved incrementally and is established considering a set of equations composed by constitutive and multiaxial notch correction equations. Additionally, a kinematic cyclic plasticity model was included. An equivalent model based on the Finite Element Method was used for comparison purposes. The comparison was made in terms of multiaxial fatigue damage parameters in critical planes, according to fatigue analysis models developed by Matake and Brown & Miller. The more relevant advantage of the method over the non-linear FEM analysis is the possibility to readily obtain long elastic–plastic stress and strain histories and to perform material parameter and load case studies. The method proposed agrees with the equivalent FEM and proved to be a powerful tool for fast wheel-rail failure analysis, especially in RCF problems. [ABSTRACT FROM AUTHOR]

• FASTSIM algorithm implementation in Abaqus to consider slipping and adhesion zones of the wheel/rail contact patch. • XFEM rolling contact fatigue (RCF) analysis of a 60E1 rail profile considering creepages. • Validation of the developed rail model with data available in the literature. • Sensitivity analysis to determine the influence of contact conditions on the fatigue life of rails. 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. [ABSTRACT FROM AUTHOR]

• The wear performance of the defected rail materials under various slip ratios and contact stresses was investigated. • The surface damage of the defected rail materials under various slip ratios and contact stresses was studied. • The effect of slip ratio and contact stress on crack propagation mechanisms near the dent was discussed. The defects on rail surface may have negative effects on the rolling contact fatigue (RCF) performance of the rail materials. This investigation researched on the RCF behaviors of the defected rail materials under various slip ratios and contact stresses. The results show that both the wear loss and the average crack length increase if the slip ratio or the contact stress increases. Moreover, the surface damage characteristics change from simple adhesion spots to significant fatigue crack grouping when slip ratio and contact stress rise. Finally, the experimental results also highlight that the slip ratio provides the deformation area for crack initiation whereas the contact stress accelerates the crack propagation by emphasizing the geometric effects. [ABSTRACT FROM AUTHOR]

• Cause for welded slide plate failure was investigated and analyzed. • Optimization scheme for welded slide plate failure was proposed. • Fatigue performance of old and new product was compared by fatigue simulation. • Strength performance of old and new product was compared by laboratory test. The wheel-rail contact relationship in turnout is more complicated than that in regular track, which will increase the dynamic wheel-rail interaction. The slide plate, being important component of turnout, is prone to produce fatigue damage under the cyclic action of wheel-rail contact force. In this paper, an investigation and analysis has been done on the fatigue damage of welded slide plate, tongue depressor fracture and weld separation. The structural optimization schemes are proposed for various failure modes. The fatigue performance of slide plate for two schemes is evaluated and compared by simulation. The strength performance of slide plate for two schemes is compared by laboratory test. In simulation, two models were established to analyse the wheel-rail dynamic interaction of vehicle-track system and stress characteristics of slide plate, respectively. The fatigue life of the slide plate for two schemes were evaluated and compared, based on the fatigue damage theories. During the test, the ultimate strength of tongue depressor and bond strength between the slide platform and the base plate for two schemes, were tested and compared. The simulation and test results showed that the fatigue and strength performance of slide plate have increased reasonably after optimization. It can provide reference for design of slide plate. [ABSTRACT FROM AUTHOR]

• Residual stress affects crack tip displacements of rail cracks. • CTSD amplitude increases with increasing wheel-rail friction coefficient. • Oblique crack propagates as the combined type of II/III dominated by type II. Fatigue crack is one of the main damages that reduce rail service life and raise rail maintenance costs. In this paper, a three-dimensional elastic–plastic finite element model of wheel-rail contact is established, in which a three-dimensional oblique crack is inserted in the rail. Taking crack tip displacements as fracture parameters, the effect of residual stress on fatigue crack propagation of rails is quantitatively analyzed, and the fatigue crack propagation mechanism of rails under the combined action of wheel load and residual stress are studied. Results show that crack tip displacements under the action of wheel load are quite different from that under the combined action of wheel load and residual stress. For the oblique crack with crack tip entering the residual tensile stress zone, crack tip sliding displacement amplitude increases with the increase of wheel-rail friction coefficient. Under the combined action of wheel load and residual stress, the oblique crack propagates as the combined type of II/III dominated by type II. [ABSTRACT FROM AUTHOR]