Rolling Contact Fatigue Damage Research Articles

Influence of wheel and rail profile shape on the initiation of rolling contact fatigue cracks at high axle loads

ABSTRACTThe influence of wheel and rail profile shape features on the initiation of rolling contact fatigue (RCF) cracks is evaluated based on the results of multi-body vehicle dynamics simulations. The damage index and surface fatigue index are used as two damage parameters to assess the influence of the different features. The damage parameters showed good agreement to one another and to in-field observations. The wheel and rail profile shape features showed a correlation to the predicted RCF damage. The RCF damage proved to be most sensitive to the position of hollow wear and thus bogie tracking. RCF initiation and crack growth can be reduced by eliminating unwanted shape features through maintenance and design and by improving bogie tracking.

The role of lanthanum oxide on wear and contact fatigue damage resistance of laser cladding Fe-based alloy coating under oil lubrication condition

This study explores the role of lanthanum oxide on the wear and contact fatigue damage resistance of laser cladding Fe-based alloy coating on the wheel and rail materials under oil lubrication condition using a rolling–sliding wear machine. The laser cladding Fe-based alloy coating on the wheel/rail materials significantly improves the wear and rolling contact fatigue damage resistance of rollers. La as a surface active element is easy to distribute mostly over the grain boundary and then the use of lanthanum oxide is beneficial for refining the grain and microstructure of cladding coating. An optimum amount of 1.2% La2O3 content is given for achieving outstanding wear and contact fatigue damage resistance of laser cladding Fe-based alloy coating.

Lateral heat conduction based eddy current thermography for detection of parallel cracks and rail tread oblique cracks

Rail tread oblique crack, initiated by rolling contact fatigue (RCF) damage, is one of the most significant phenomena and has serious influence on rail industry. Electromagnetic non-destructive testing (EM NDT) methods are usually used in rail regular inspection. However, the conventional EM NDT methods based on eddy current field distribution are difficult to detect the cracks parallel to the inductive coil (parallel cracks) and natural oblique cracks. This paper studied lateral heat conduction (LHC) induced by eddy current for detection of these defects. The proposed method was verified through both numerical and experimental studies as well as the investigation of characteristic of LHC. Due to significant temperature gradient in the direction of lateral heat conduction, the spatial derivative and gradient were proposed to improve the defect detectability on the thermograms. Finally, the test of natural oblique cracks on a rail was conducted to validate the proposed methods.

The Progression of Surface Rolling Contact Fatigue Damage of Rolling Bearings with Artificial Dents

The mechanism of surface rolling contact fatigue (SRCF) in rolling bearings is investigated by means of dedicated experiments and numerical simulations of the damage progression. Pre-indented inner ring raceways in roller and ball bearings were extensively endurance tested. It is observed that spalls originated from indentations in ball bearings develop initially at the trailing edge of a pre-indented raceway with a typical V-shaped spall. In this location, the raceway material first detaches at the edge of the dent, forming a V-shaped damaged area, before growing at fast rate along the raceway. Roller bearings, however, follow the well-known behavior of slowly growing the spall directly across the raceway, before continuing along the rolling path. An existing physically based rolling contact fatigue model able to predict (1) material particle detachment by surface rolling contact fatigue and (2) the effect of the elastohydrodynamic lubrication (EHL) in such a process is adapted and used to simulate the surface damage growth in the two rolling bearing configurations. It is found that the model is able to describe well the experimental results, shedding some light on the developing mechanism of the two SRCF configurations. The difference between ball and roller bearing damage inception and progression is explained and discussed in detail.

Study of ball bearing fatigue damage using vibration analysis: application to thrust ball bearings

This paper presents a study based on the damage due to the fatigue life of thrust ball bearings using vibratory analysis. The main contribution of this work lies in establishing a relation between modal damping and the rolling contact fatigue damage of the thrust ball bearing. Time domain signals and frequency spectra are extracted from both static and dynamic experiments. The first part of this research consists in measuring the damping of damaged thrust ball bearings using impact hammer characterization tests. In a second part, indented components representing spalled bearings are studied to determine the evolution of damping values in real-time vibration spectra using the random decrement method. Dynamic results, in good agreement with static tests, show that damping varies depending on the component's damage state. Therefore, the method detailed in this work will offer a possible technique to estimate the thrust ball bearing fatigue damage variation in presence of spalling.

Improvement of vehicle–turnout interaction by optimising the shape of crossing nose

Proper rail geometry in the crossing part is essential for reducing damage on the nose rail. To improve the dynamic behaviour of turnout crossings, a numerical optimisation approach to minimise rolling contact fatigue (RCF) damage and wear in the crossing panel by varying the nose rail shape is presented in the paper. The rail geometry is parameterised by defining several control cross-sections along the crossing. The dynamic vehicle–turnout interaction as a function of crossing geometry is analysed using the VI-Rail package. In formulation of the optimisation problem a combined weighted objective function is used consisting of the normal contact pressure and the energy dissipation along the crossing responsible for RCF and wear, respectively. The multi-objective optimisation problem is solved by adapting the multipoint approximation method and a number of compromised solutions have been found for various sets of weight coefficients. Dynamic behaviour of the crossing has been significantly improved after optimisations. Comparing with the reference design, the heights of the nose rail are notably increased in the beginning of the crossing; the nominal thicknesses of the nose rail are also changed. All the optimum designs work well under different track conditions.

Occurrence of High Pressure Spike in Unidirectional Start–Stop–Start Point Contacts

The transient film thickness and pressure distributions in point elastohydrodynamic lubrication (EHL) contacts during start–stop–start motion are discussed based on experimental and numerical analyses. When the machine element starts to move after the stopping, where the oil is entrapped between two surfaces, the pressure at the exit area increases very much. The pressure increase depends markedly on the overall film thickness before the stopping of the motion, but is hardly controlled by the acceleration after the stopping. It can be considered that this phenomenon affects the rolling contact fatigue damage.

Multiphysics computational analysis of white-etch cracking failure mode in wind turbine gearbox bearings

Wind energy is currently one of the most promising and the fastest-growing installed alternative-energy production technologies. It is anticipated that by 2030, at least 20% of the US energy needs will be provided by this form of energy. The economics of wind energy require that wind turbines (convertors of wind energy into electrical energy) be able to operate for at least 20 years, with only regular maintenance. Unfortunately, many wind turbines require major repairs after only 3–5 years in service, mainly due to the failure of their gear boxes. It is this lack of gear box reliability which is currently compromising wind energy economics. In the present work, a multiphysics computational methodology has been developed and used to analyze the problem of white-etch cracking, one of the key processes responsible for the premature failure of gearbox roller bearings. The multiphysics methodology includes: (a) quantum-mechanical calculations of the hydrogen dissolution and the accompanying grain boundary embrittlement phenomena; (b) atomistic-level kinetic Monte Carlo analysis of hydrogen diffusion from the crack wake into the adjacent unfractured material; (c) cohesive zone type modeling of the intergranular fracture processes; and (d) a conventional displacement-based finite element analysis of the kinematic and structural response of the bearing under service loading conditions. The results obtained clearly revealed the operation of the white-etch cracking phenomena and their possible interaction with the conventional rolling-contact fatigue damage processes.

Subsurface Rolling Contact Fatigue Damage Distribution of Backup Roll After Periodic Dressing

In this paper, subsurface rolling contact fatigue damage distribution of backup rolls after used one time and periodic dressing are theoretically analyzed. The theoretical model established is verified by experiments test on ring samples and dissection part cut from backup rolls used in production. The results reveal that the subsurface damage of ring samples and dissection parts characterized by hardness test is consistence well with the distribution predicted by theoretical model. The maximum subsurface damage of backup rolls gradually moves toward the surface and the spalling of backup rolls can be prevented if suitable dressing amount be selected.

Wheel damage on the Swedish iron ore line investigated via multibody simulation

The Swedish iron ore company LKAB uses freight wagons with three-piece bogies to transport iron ore from its mines in Kiruna and Malmberget to the ports at Luleå and Narvik. A simulation model of the freight wagon is built using the multibody simulation code GENSYS. The objective is to investigate possible sources of rolling contact fatigue (RCF) of the wheels given the high level of observed damage. A parameter study is performed on the effects of vertical track stiffness and viscous damping that occur as a result of seasonal variations of the track condition. Another parameter study is carried out on the influence of the wheel/rail friction coefficient as in winter time the climate is very dry along most parts of the Malmbanan line. The impact of track gauge, track quality and cant deficiency on RCF is also studied. Comparing the calculated and observed RCF locations on wheels, attempts are made to find a relation between wear number and RCF damage. To detect the surface-initiated fatigue a so-called shakedown map is used. It is shown that RCF occurs on the tread of the inner wheels while negotiating curves with below an approximately 450 m radius. It is also shown that cant deficiency can be helpful for the vehicles to negotiate curves and to reduce the risk of RCF, however, on the other hand it may increase the track forces and in severe cases result in flange climbing. Lateral track irregularities and a large track gauge result in small contact areas and can lead to a higher risk of RCF. In cold dry climate conditions, as the water content in air drops significantly, the wheel/rail friction coefficient increases and when the material in the wheel begins to behave in a brittle manner, the risk of RCF is significantly increased, especially when the wear rate is not high enough to remove the initiated cracks.

The Influence of Wheel/Rail Contact Conditions on the Microstructure and Hardness of Railway Wheels

The susceptibility of railway wheels to wear and rolling contact fatigue damage is influenced by the properties of the wheel material. These are influenced by the steel composition, wheel manufacturing process, and thermal and mechanical loading during operation. The in-service properties therefore vary with depth below the surface and with position across the wheel tread. This paper discusses the stress history at the wheel/rail contact (derived from dynamic simulations) and observed variations in hardness and microstructure. It is shown that the hardness of an “in-service” wheel rim varies significantly, with three distinct effects. The underlying hardness trend with depth can be related to microstructural changes during manufacturing (proeutectoid ferrite fraction and pearlite lamellae spacing). The near-surface layer exhibits plastic flow and microstructural shear, especially in regions which experience high tangential forces when curving, with consequentially higher hardness values. Between 1 mm and 7 mm depth, the wheel/rail contacts cause stresses exceeding the material yield stress, leading to work hardening, without a macroscopic change in microstructure. These changes in material properties through the depth of the wheel rim would tend to increase the likelihood of crack initiation on wheels toward the end of their life. This correlates with observations from several train fleets.

3D characterisation of RCF crack networks

Rolling contact fatigue (RCF) damage is becoming more frequent with increased traffic and loading conditions in the railway industry. Defects which are characterized by a two-lobe darkened surface and a V-shaped surface-breaking crack are often so-called squats. The origination and propagation of squats in railway rails is the topic of many recent studies; the associated crack networks develop with complicated geometry near the surface of rails that is difficult to characterise using most non-destructive methods. The cracks can be examined with repeated metallographic sectioning, but the process is time-consuming and destructive. In order to reduce time, as well as information and material loss, high-resolution and high-energy X-ray imaging of railway rails was done in the current study. Combining the exposures from a range of angles using image analysis, a 3D representation of the complex crack network is achieved. The latter was complemented with metallographic sectioning to determine the accuracy of prediction of the geometrical reconstruction.

A Parametric Investigation of Surface Initiated Rolling Contact Fatigue Using the Asperity Point Load Mechanism

Rolling contact fatigue (RCF) will eventually become an issue for machine elementsthat are repeatedly over-rolled with high contact loads and small relative sliding motion. Thedamage consists of cracks and craters in the contact surfaces. Asperities on the contact surfacesact as local stress raisers and provide tensile surface stresses which can explain both initiationand propagation of surface initiated RCF damage. A parametric study was performed to inves-tigate the contribution of surface roughness, friction and a residual surface stress to the RCFdamage process. The effects on initiation, crack path and fatigue life at both early and devel-oped damage were examined for a gear application. Both a one-parameter-at-a-time approachand a 2-level full factorial design were carried out. Surface roughness and local friction prop-erties were found to control crack initiation, whereas the simulated crack path was primarilyaffected by the residual surface stress, especially for developed damage. Reduced surface rough-ness, improved lubrication and a compressive residual surface stress all contributed to increasethe simulated fatigue life. The asperity point load model could predict effects on RCF that areobserved with experiments. The results further support the asperity point load mechanism asthe source behind surface initiated RCF.

Research on the Approach for the Assessment of Subsurface Rolling Contact Fatigue Damage

In this paper, the distribution of different critical stresses, which were used in previous correlation articles for the assessment of subsurface rolling contact fatigue damage, was analyzed. The rationality of orthogonal shear stress was selected as the key stress controlling the subsurface rolling contact fatigue damage was clarified. Base on the linear fatigue damage accumulative theory and the modification equation for the range of asymmetrical stress, the influence of friction on subsurface rolling contact fatigue damage was studied. The results show that the subsurface orthogonal shear stress is a completely symmetrical stress when the friction coefficient is zero, while it is an asymmetrical stress with considering the friction. The stress ratio of subsurface orthogonal shear stress and subsurface rolling contact fatigue damage is increased with the increasing of friction.

Development and validation of a wheel wear and rolling contact fatigue damage model

This paper summaries the development of a damage model to predict the deterioration rates of the wheel tread in terms of wear and rolling contact fatigue (RCF) damage. The model uses a description of a fleet's route diagram to characterise the duty cycle of the vehicle in terms of curve radius, cant deficiency and traction/braking performance. Using this duty cycle a large number of vehicle dynamics simulations are automatically conducted to calculate wheel–rail contact forces and predict the formation of wear and RCF damage, using a combination of the Archard and frictional energy-based (Tγ) damage models.The damage models have been validated using observation data (wear rates and maximum observed RCF damage) acquired from a range of vehicle fleets in Great Britain (GB). Results from the validation of the model are presented along with a review of the wheel turning and observation data.A piece-wise linear regression is fitted to the wear and RCF parameters predicted from the model to determine the damage rates for each wheelset type on the vehicle. These damage rates are used within the recently developed Wheelset Management Model (WMM) to describe how the attributes of the wheel (i.e. wheel diameter, profile shape and tread damage) deteriorate over time and trigger a maintenance or renewal activity when the condition of the wheel matches a particular limiting value.This work formed part of the rail industry research programme managed by the Rail Safety and Standards Board (RSSB), and funded by the Department for Transport, to increase the rolling stock functionality of the Vehicle Track Interaction Strategic Model (VTISM) tool.

Investigation of a novel rolling contact fatigue/wear competitive life test machine faced to surface coating

A novel rolling contact fatigue (RCF)/wear competitive life test machine based on double-roll mechanism was designed to investigate the RCF/wear failure mode and predict the competitive life regularity of surface coatings. The test machine was designed for variable slip ratio to simulate the complex service conditions. The failure can be monitored using signals which are acquired from acoustic emission (AE) of the contacting rollers. In the experimental studies, the typical morphologies of RCF damage such as pits, surface abrasion, and delamination were observed. The effectiveness of the AE signals used as a RCF failure monitoring tool was analyzed. The P–N and P–S–N plots were established to predict the life regularity of surface coatings.

Modelling of Surface Initiated Rolling Contact Fatigue Damage

A parametric study was performed to investigate the contribution of surface roughness, friction and a constant residual surface stress to the rolling contact fatigue damage process. The effects on initiation, crack path and fatigue life were examined for a gear application. The asperity point load model could predict effects on rolling contact fatigue that are observed with experiments. The study of a ring/cone crack subjected to a rolling contact fatigue load allowed to explain the v-shaped cracks typical for surface initiated spalling. The results further support the asperity point load mechanism as a source behind surface initiated rolling contact fatigue.

NDI of Rail Squats and Estimating Defect Size and Location Using Lock-In Thermography

Rail squats are a form of near surface rolling contact fatigue damage found in rail heads. Currently, the most popular method to detect the rail squats is utilizing ultrasonic techniques to determine their presence and measure their depths. This technique needs to be direct contact between the probe and the rail head, with a coupling fluid in at the interface. Other weaknesses of these ultrasonic techniques include false detections as well as missed detections. Infrared thermography is a relatively new non-destructive inspection technique used for a wide range of applications but is not used for rail squat detection. Lock-in thermography is a non-destructive inspection technique that can be used for the detection of near surface defects. It utilizes an infrared camera to detect the thermal waves and then produces a thermal image, which displays the local thermal wave variation in phase or amplitude. In inhomogeneous materials, the amplitude and phase of the thermal wave carries information related to both the local thermal properties and the nature of the structure being inspected. This comparison is then used to determine the phase angle difference (Δf) between the input and the thermal response of the object. The aim of this paper is to determine whether lock-in thermography can be used to firstly locate squats in rails, and secondly measure their depths. It has demonstrated the feasibility for using such a technique in generating thermal responses that could be adequately utilized for the purpose of defect characterization.

Acoustic emission monitoring and failure mechanism analysis of rolling contact fatigue for Fe-based alloy coating

The aim of present study is to monitor rolling contact fatigue (RCF) behavior and analyze failure mechanism of the coating by acoustic emission (AE) technology. The results show that AE amplitude and counts are sensitive to RCF damage process, and variation regularities are different during different damage stages. Spalling is the key failure mode. RCF damage process is composed of five stages, such as elastic deformation, plastic deformation, crack initiation and propagation, crack stable growth, and unstable growth. Fatigue cracks are liable to initiate and grow along the direction of defects within the coating, such as pores and cracks.

Surface initiated rolling contact fatigue based on the asperity point load mechanism—A parameter study

The influence of asperity size, friction and residual surface stress on surface initiated rolling contact fatigue damage was investigated using the asperity point load mechanism. A parametric study was performed in two steps, first with a classic one-parameter-at-a-time approach, then as a 2-level full factorial design. The effect on fatigue initiation, damage size and spalling life for both early and developed spalling damage was examined for a gear application. Simplified response surfaces were derived as an engineering design tool for improved spalling resistance. The parametric investigation suggested that among the investigated parameters, reduced asperity height and local asperity friction will have the largest effect on the crack initiation risk. The simulations agreed with the engineering experiences that reduced surface roughness improves rolling contact fatigue resistance and that improved lubrication lengthens spalling lives and decreases fatigue risk. With compressive residual surface stresses the predictions suggested reduced fatigue risk and substantially decreased depth of individual spalls. Finally, predictions of experimentally observed effects of changing asperity size, friction and residual surface stress on spalling further motivates the asperity point load mechanism as the source behind surface initiated rolling contact fatigue.