Rolling Contact Fatigue Crack Growth Research Articles

Effect of creepages on stress intensity factors of rolling contact fatigue cracks

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 KII and KIII 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.

On the growth of rolling contact fatigue cracks using weight functions

The present paper discusses the estimation of the stress state of Rolling Contact Fatigue (RCF) cracks according to linear elastic fracture mechanics, by making use of the weight function to obtain the Stress Intensity Factors. The weight functions are considered for both the mode I and mode II Stress Intensity Factor and are based on existing formulations for an inclined edge crack in a finite width plate for which Green’s functions are derived by means of a numerical methods. The Stress Intensity Factors been predicted for a side crack having an inclination angle typical for RCF defects in a plate of finite width supported by an elastic foundation and subjected to a moving wheel load, modelled as a patch load. The Stress Intensity Factors are obtained by superimposing the bending moment due to the moving load, and local stresses due to normal pressure and tangential tractions resulting from the contact with the wheel. These local stresses are determined using theoretical solutions partially available in the literature. The Stress Intensity Factors obtained are compared with the results of numerical models presented in the literature regarding the RCF crack growth.

The crack propagation path for a system of surface and subsurface cracks and their interactions due to rolling contact fatigue

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.

Numerical simulation of rolling contact fatigue crack growth in rails with the rail bending and the frictional contact

Due to the repeated passages of the wheels, the rail is subjected to time-dependent, multiaxial, non-proportional, mixed mode cyclic loading. Under these conditions of loading, the fatigue cracks can appear in the surface or subsurface of the rails. This paper attempts to investigate the multiaxial fatigue crack growth in rails using 3D numerical simulations taking into account the frictional contact between crack faces and the rail bending. Firstly, a quick description is given of the two-scale strategy (global structure and local interface) for the cracked body problem with frictional contact between the crack faces. In this strategy, a stabilized three-field weak formulation is proposed to avoid possible oscillations in the local solution linked to the LBB condition. This formulation is discretized within the framework of the eXtended Finite Element Method (XFEM). Then, the LATIN non-linear solver is used to solve the two-scale problem. Secondly, we focus on the 3D railway track model with an initial crack on the rail surface. The sleepers and the rail fastenings are modelled by introducing constraints on the vertical displacement of some nodes on the rail foot. This 3D cracked rail model is used to simulate the propagation of different types of crack (in curve, in straight line) under the multiaxial wheel-rail contact loading. Finally, a parametric study is investigated in order to clarify the influence of the friction coefficient between crack faces, the position of the crack in relation to the sleepers and the stiffness of the track on the crack growth behavior.

Effect of wear on rolling contact fatigue crack growth in rails

The purpose of this paper is to analyze the influence of the load direction and the phenomenon of wear on rolling contact fatigue crack growth. For this purpose, a UIC60 rail with accurate geometry using FEM is studied. In this regard, a three-dimensional finite element model is provided. The maximum stress caused by wheel/rail contact for a new/worn wheel profiles was obtained using such model. Then, using Franc 3D software, during stress analysis for different situations of wheel, different values of stress intensity factors are obtained. The behavior of crack under fatigue loading was studied using a three-dimensional modeling.

Numerical study on fatigue crack growth in railway wheels under the influence of residual stresses

Accurate prediction of fatigue crack growth on railway wheels and the influence of residual stresses by finite element method (FEM) modeling can affect the maintenance planning. Therefore, investigation of rolling contact fatigue and its effect on rolling members life seem necessary. The objective of this paper is to provide a prediction of rolling contact fatigue crack growth in the rail wheel under the influence of stress field from mechanical loads and heat treatment process of a railway wheel. A 3D nonlinear stress analysis model has been applied to estimate stress fields of the railway mono-block wheel in heat treatment process. Finite element analysis model is presented applying the elastic–plastic finite element analysis for the rail wheel under variable thermal loads. The stress history is then used to calculate stress intensity factors (SIFs) and fatigue life of railway wheel. The effect of several parameters, vertical loads, initial crack length and friction coefficient between the wheel and rail, on the fatigue life in railway wheels is investigated using the suggested 3-D finite element model. Three-dimensional finite element analysis results obtained show good agreement with those achieved in field measurements.

Rolling Contact Fatigue Crack Growth Prediction by the Asperity Point Load Mechanism

The crack path and growth life of surface initiated rolling contact fatigue was investigated numerically based on the asperity point load mechanism. Data for the simulation was captured from a gear contact with surface initiated rolling contact fatigue. The evolvement of contact parameters was derived from an FE contact model where the gear contact had been transferred to an equivalent contact of a cylinder against a plane with an asperity. Crack propagation criteria were evaluated with practically identical crack path predictions. It was noted that the trajectory of largest principal stress in the uncracked material could be used for the path prediction. The mode I fracture mechanism was applicable to the investigated rolling contact fatigue cracks. The simulated path agreed with the spall profile both in the entry details as in the overall shape, which suggested that the point load mechanism was valid not only for initiation but also for rolling contact fatigue crack growth. Different equivalent stress intensity factor ranges were used to estimate the fatigue life, which agreed with the life of the investigated gear wheels.

Rolling contact fatigue crack path prediction by the asperity point load mechanism

The crack path of surface initiated rolling contact fatigue was investigated numerically based on the asperity point load mechanism. Data for the simulation was captured from a gear contact with surface initiated rolling contact fatigue. The evolvement of contact parameters was derived from an FE contact model where the gear contact had been transferred to an equivalent contact of a cylinder against a plane with an asperity. Five crack propagation criteria were evaluated with practically identical crack path predictions. It was noted that the trajectory of largest principal stress in the uncracked material could be used for the path prediction. Different load types were investigated. The simplified versions added some understanding but the full description with cylinder and asperity pressures was required for accurate results. The mode I fracture mechanism was applicable to the investigated rolling contact fatigue cracks. The simulated path agreed with the spall profile both in the entry details as in the overall shape, which suggested that the point load mechanism was valid not only for initiation but also for rolling contact fatigue crack growth.

A study of rolling contact fatigue crack growth in U75V and U71Mn rails

Rolling contact fatigue (RCF) failure is a permanent and quite severe problem and hence of major concern to the modern railway industry. The selection of rail material should be based on a well-founded understanding of RCF. An analysis of the chemical composition, mechanical performance and microstructure was performed on U75V and U71Mn rail samples with oblique cracks taken from Guangzhou–Shenzhen railway. The results indicate that the strength character of U75V rail is superior to U71Mn rail. The crack propagation angle to the surface of U71Mn rail is smaller than that of U75V rail. A mixture of intergranular and transgranular fracture was found dominant in the process of fatigue crack propagation of U71Mn rail; in comparison, the dominant fracture mode of U75V rail is transgranular and the crack is easier to propagate at a relatively higher rate. The analysis shows that U71Mn rail is more suitable for the high-speed railway.

Very early stage rolling contact fatigue crack growth in pearlitic rail steels

Abstract This paper reports on metallurgical characterisation of small cracks in pearlitic steels, using observations from both twin disc tests and rails removed from service, plus methods to determine three-dimensional (3D) aspects of such cracks. Tests to varying fractions of rolling contact fatigue (RCF) life have been assessed, based on twin disc tests where “average 100% RCF life” has been defined by eddy current detection of cracks between 200 and 800 μm in depth. Contact surface features and microstructural alterations have been mapped against near-surface strain and compared with worn rail examinations. Initial crack growth along favourably aligned and strained, prior-austenite (PA) grain boundaries, particularly if the boundary contains pro-eutectoid (PE) ferrite, was found to be restricted or halted at the PA grain limit or where the boundary altered to be less-favourably aligned. For samples with up to 55% RCF life, initial crack propagation length was still less than the average PA grain size. 3D aspects of this early growth and the deformed PA grain shapes were found to be linked to ratcheting flakes and flake cracks on test disc and rail contact surfaces. The results have shown how initial RCF crack propagation is very microstructurally influenced.

Rail rolling contact fatigue dependence on friction, predicted using fracture mechanics with a three-dimensional boundary element model

Rolling contact fatigue crack growth continues to affect many railways worldwide. It is most often controlled through rail grinding in a preventive maintenance strategy, but to plan the required frequency and depth of grinding, prediction of crack growth rates has a vital role. This paper presents crack growth rate results from a new three-dimensional rail model containing an inclined surface breaking rolling contact fatigue crack. The calculations are based on a shear mode of crack growth, driven by the Hertzian contact pressure on the railhead and moderated by friction between the crack faces (“crack face friction”). The results from the model show good correlation with those from the previously published work in the area, with particularly good agreement at higher levels of surface friction coefficient. Applying the new model to a range of surface and crack face friction coefficients predicted that crack growth rate will rise with reduced internal crack face friction at all crack sizes. For small cracks (2 and 5 mm radius) rates were predicted to rise with increased surface traction, but this trend was reversed at larger crack sizes (10 and 19 mm radius). Identical trends were found when the modelling was repeated using the previously developed half-space based “2.5d” model, indicating that although this older model cannot represent the rail geometry its high speed means it remains a useful tool for investigating the effects of contact parameters on rail rolling contact fatigue. The next study in this area could therefore consider if there is a uniform or crack size related ratio for mapping 2.5d results to three-dimensional rail geometry to produce closer agreement in crack growth rates as well as trends. For the three-dimensional model, consideration of alternative crack morphologies and movement of the contact running band away from the rail centreline would provide additional data on the effect of rail grinding and re-profiling on rolling contact fatigue.

Computer simulation of strain accumulation and hardening for pearlitic rail steel undergoing repeated contact

This paper presents a validated model of plastic strain accumulation in railway rail steel under repeated wheel-rail contact. Such contacts subject the rails to severe stresses, taking the material local to the contact beyond yield, and leading to the incremental accumulation of plastic deformation (ratheting) as wheels pass. This process is at the root of several rail wear and rolling contact fatigue crack growth mechanisms. Existing plasticity models are inadequate for modelling the strain accumulation taking place in this material, which is under high hydrostatic compression (of the order of 1 GPa) and is severely anisotropic. The model described here is based on a ratcheting law derived from small-scale twin-disc rolling-sliding contact experiments and simulates tens of thousands of ratcheting cycles and the corresponding strain hardening in a few minutes on a personal computer. Results indicate that, to model these processes successfully, and to represent correctly the high levels of ductility seen in rail steels under compressive load, stress-strain data generated under high hydrostatic compression are required.

A Predictive Rolling Contact Fatigue Crack Growth Model: Onset of Branching, Direction, and Growth—Role of Dry and Lubricated Conditions on Crack Patterns

Complex crack networks are initiated in rails under Rolling Contact Fatigue. This paper attempts to model the RCF crack propagation with a particular emphasis on the branching conditions and the parameters that play a role on them. The numerical tool proposed rests on the combination of the author’s RCF model, Hourlier and Pineau’s criterion for the branch prediction and experimental data and the corresponding models for fatigue crack extension that are derived from a Joint European project. Parametric studies on the influence of (i) residual stresses, (ii) both interfacial crack and wheel/rail contact frictional effects, (iii) neighboring crack are conducted to reach a better understanding of the RC crack propagation behavior and more particularly the branch conditions, i.e., the length of the primary crack prior to branch formation and the branch direction.