Rolling Contact Surface Research Articles

Effects of hydrogen on the formation of nanocrystalline at rolling contact surface of bainitic rail steel

A newly discovered peculiar microstructure at the rolling contact surface of bainitic rail steel has been investigated via positron annihilation technique and X-ray diffraction. The results show that the nanocrystalline layer is produced through low-temperature dynamic recrystallization. After hydrogen charged, low temperature dynamic recrystallization has been inhibited by hydrogen, and nanocrystalline layer at the surface decreases or disappears.

Wear Failure of PEEK-Alumina Ball Bearings in Dry Rolling Contact at 600 rpm - Part 2: Observation of Wear on Retainer

In our previous paper[6], the effects of the retainer wear failure on the friction torque were investigated. In the present paper, to research the failure of the retainers of the PEEK-alumina ball bearings tested under dry rolling contact, the upper and bottom surfaces and the sections of the retainer pockets were observed. The wear damage was found on the surface of the upper and bottom surfaces. On the sections of the pocket, the changes due to wear at the pocket edge was found. On the worn curves of the sections, large scatter of the curvature center positions were numerically calculated in both specimens. The balls moved relatively for the retainer unit to the upper or bottom sides. These results indicate that the wear changed the pocket shape, and the ball could not become to keep the position for the retainer unit. The wear of the pocket caused the failure of the retainer.

A modified model of Lundberg-Palmgren rolling contact fatigue formula considering the effects of surface treatments

The Lundberg-Palmgren (L-P) fatigue life formula, as a statistical fatigue theory, has been widely used in the industry. However, its direct applicability is limited to the components treated by surface strengthening technologies. Rolling contact fatigue tests and surface integrity measurements of American Iron and Steel Institute (AISI) 9310 rollers with several surface treatments were performed to address this issue. Based on these results, a modified L-P fatigue model was proposed, enabling the consideration of surface modification including surface roughness, residual stress, and hardening introduced by different surface treatments. Compared with the original L-P fatigue formula, its results are more accurate for surface strengthened specimens. Furthermore, this method can assess the contact fatigue life of gears treated by surface strengthening techniques.

Effect of different laser texturing patterns on rolling contact surface and its tribological & fatigue life behavior on 100Cr6 bearing steel

The effects of laser texturing technology on the tribological performance of tapered roller bearings in terms of fatigue life, friction, and wear are studied for the first time. The influence of diameter, height and density of the circular-shaped dimples is thoroughly analyzed, first on flat samples, and the most encouraging results are upscaled to components. This research demonstrates the advantages that surface texturing can bring to the most demanding applications involving rolling surfaces under lubrication regime. The experiments show a torque reduction up to 18% and very promising results in fatigue life tests.

Prediction system of rolling contact fatigue on crossing nose based on support vector regression

It is essential to assess the rolling contact fatigue (RCF) of turnouts and maintain them in advance. It saves a lot of money while protecting the safety of railway operations. In Germany, the damage on rails, especially crossing noses, mainly depends on the subjective judgment of experts. There are no objective and comprehensive evaluation criteria. This paper presents the application of image processing and supervised machine learning algorithms to crossing nose fatigue judgment. The fatigue characteristics of the crossing nose rolling contact surface along the life cycle of the crossing nose are analyzed. The study used crack information from magnetic particle inspection (MPI) images of crossing nose surfaces. It uses basic image processing methods to collect physical information about features of fatigue cracks in images. Existing feature selection methods are used to exclude irrelevant features and retain valuable features. And we select the best feature selection method through the regression results. Statistically significant crack features and combinations that depict the surface fatigue state are found. In this paper, by comparing several usually machine learning regression algorithms, it is found that the supervised learning of support vector machine regression (SVR) has achieved the best results in the regression fitting of the crack feature data in this paper. The regression results form a simple system to evaluate the life cycle of crossing nose. The system finds the location of cracks that can create dangerous defects in the crossing nose surface. The research result consists of the early prediction of rail contact fatigue.

In-situ generation process and properties of nanocrystalline layer in bainitic steel surface during rolling contact

The formation process of nanocrystalline layer (NL) on rolling contact surface of bainitic steel are studied. The results show that the surface repeatedly goes through a cycle of NL generation, spalling and production. The decrease of elastic modulus of the steel surface indicates that fatigue properties have begun to damage.

Estimation of fatigue life parameters of an Alumino Thermic weld on UIC60 rail joint using LEFM

At wheel track contact point, the high stress concentration, poor weld quality, and heterogeneity of weld material are the main factors that cause fatigue crack on any rail weld. Railway network agencies are concerned about the safety of the railway track when it comes to detecting and fixing weld faults to avoid vehicle derailment and loss of lives. This study analysed a numerical simulation of fatigue crack and its evolution under loaded service condition. A 3-D CAD wheel rail weld assembly model was built to study an AT welded joint under fatigue, and for stress concentration factor (SIF) calculation. The results are found by inserting a semi elliptical crack on the rail weld head surface with ANSYS, and then numerical simulation has been performed to get the different three modes of SIF at rail weld crack. The analysis findings data was recorded with critical fracture parameters of SIFs and its number of cycles to failure using LEFM technique and respective results have been plotted. With ANSYS the stress intensity on a crack will be resulted. By using numerical method, the critical crack size and number of cycle load with fatigue life of rail would be determined. The numbers of rail weld inspection per year has been determine by using the maximum number of cycle. The aim of this paper is to develop an effective inspection and maintenance frequency based on rolling contact surfaces crack propagation analyse. This will help to prevent the occurrence of rail failure by taking the required action at the right time, and extend the rail life expectancy, reduce the rail maintenance work and its cost.

Applications of vibro-acoustic measurement and analysis in conjunction with tribological parameters to assess surface fatigue wear developed in the roller-bearing system

Rolling-element bearings are the most commonly used components in all rotating machinery. The variations in the operating conditions such as an increase in the number of operating cycles, load, speed, service temperature, and lubricant degradation result in the development of various defects such as pitting, spalling, scuffing, scoring, etc. The defects that appeared on rolling contact surfaces cause surface deterioration and change in the vibration and sound levels of the bearing system. The present experimental investigations are aimed at assessing the surface fatigue wear that appears on the contact surfaces of roller bearings. The studies considered the estimation of specific film thickness, analysis of surface fatigue wear developed on the rolling-element surfaces, surface roughness analysis, grease degradation analysis using Fourier transform infrared radiation, and vibration and sound signal measurement and analysis. The results obtained from the experimental investigation provide a good correlation between surface wear, vibration, and sound signals with a transition in the lubrication regimes in the Stribeck curve.

An experimental approach to study the effect of wear on traction coefficient and dynamic response of roller bearing

Cylindrical roller bearings are generally used to support rotating shafts mounted in a rotating machinery. These machine elements are prone to premature failure due to increase in friction which causes the heat generation and gradual wear on rolling contact surfaces of the bearing. Bearing failure leads to unexpected shutdown of machinery, therefore several condition monitoring methods have been developed to detect and diagnose the bearing faults. The purpose of this paper is to establish a relationship between surface roughness and wear on the traction coefficient parameter of roller bearing and corresponding dynamic response. Results obtained from the experimental investigations highlight dependency of traction coefficient and dynamic response of the bearing on wear propagation on the rolling contact surfaces.

Investigation of the electrical rolling contact degradation based on fractal theory

Rotary electrical connector is one of the key components for power source and electrical equipment connecting with rotating electrical interfaces, such as artificial space station, earth satellite, radar, wind generator, etc. Rolling contact connector (RCC) is a competitive technology compared to traditional sliding connectors for rotary electrical connecting, especially for long-life applications. In this paper, a novel coupled rolling contact structure of RCC prototype is presented. The degradation of rolling electrical contact is studied experimentally. Scanning electron microscope and confocal laser scanning microscope are utilized to obtain the gradual changes of the microscopic morphology and elemental composition on the rolling contact surfaces. A mathematical model of electrical contact based on fractal geometry is introduced to describe the contact behavior of RCC. Numerical analysis results illustrate the fractal dimension can be used as a key parameter to characterized the wear pattern. The mechanism of rolling electrical contact degradation is discussed in detail.

Effects of carbon content and hardness on rolling contact fatigue resistance in heavily loaded pearlitic rail steels

To reproduce the rolling contact fatigue (RCF) damage of rail steel used in heavy haul railways and to clarify its possible mechanism, the RCF characteristics of pearlitic steel with different carbon content and initial hardness values are evaluated using a two-disk-type machine. The results indicate that the number of spalls and the crack depth decrease with increasing carbon content of pearlitic steel even when the initial hardness is almost the same level. Furthermore, an increase in the carbon content increases the hardness of the rolling contact surface, resulting in the suppression of the plastic flow development. Results also indicate that the crack inclination angle varies depending on the carbon content. According to these results, a possible mechanism for the suppression of fatigue crack propagation in higher carbon pearlitic steel is proposed on the basis of the fracture mechanics approach.

Influence of the roughness on surface geometry of rolling contacts

The topography of the active surfaces in rolling contact depends on the surface roughness obtained by different manufacturing process technology (turning, grinding, polishing, lapping, etc.). The aim of this paper work is to evidence the influence of the surface roughness on surface geometry of rolling contacts. The experimental tests were carried out on the AMSLER machine and an experimental setup for pure rolling motion. The surfaces of the rolling samples were analyzed with SEM (scanning electron microscopy) and EDS (energy dispersive X-ray spectroscopy) techniques for structural and chemical analysis and measured with the Taylor Hobson profilometer before and after the experimental tests for surface topography.

Microscopic investigation of subsurface initiated damage of wind turbine gearbox bearings

Wind turbine gearbox bearings experience premature failures by White Structure Flaking (WSF), often occurs much earlier than their designed life of 20 to 25 years. This results in increased operational and maintenance costs due to unplanned maintenance and early replacement. The main causes and damage initiation mechanism of this premature failure are not fully understood; despite extensive research and investigation in recent years. In this paper, two planetary bearings from a failed gearbox of a multi-megawatt wind turbine are destructively investigated to characterize the subsurface microstructural damage and to understand damage initiation mechanism leading to surface WSF. The results show that the non-metallic inclusions are not the only initiator of subsurface damage. The microcracks are also initiated in the subsurface to form macrocracks which then propagate or connect to other macrocracks to reach the rolling contact surface causing WSF. The characterization of different forms of subsurface microstructural damage shows a close correlation of the maximum shear stress with the damage initiation. Butterfly wings are found to initiate from the compound type of non-metallic inclusions with low aspect ratio and to be associated with inclusion internal cracking in a direction approximately parallel to the axis of the maximum wing length.

Study of microstructural degradation of a failed pinion gear at a cement plant

Abstract The failed pinion gear assembly of a cement plant was analyzed by visual, residual stress, microstructure and mechanical property examination to determine the root cause of its failure. It is observed that the worn out region contains several surface micro cracks, especially closer to the tip (addendum) as compared to the root (dedendum) of the gear tooth profile. The surface analysis of the worn out regions showed depletion of protective chromium oxide layer at the surface and formation of iron oxide scales due to corrosion attack by lubricants, contaminants resulted in micro pitting and subsequent wear. Residual stress measurements showed tensile residual stresses at the tip (face) of the gear teeth and large compressive stresses at the root (flank) of the gear teeth. The cross-sectional microstructure examination revealed the damages due to rolling contact surface fatigue in the form of subsurface dark etched region bands and coarsened carbides in the surface. Apart from this, the difference in the tempered core microstructure below the case hardened layer between the flank and face regions lead to compressive residual stress in case of soft core and tensile stress in case of harder core respectively. The concentration of tensile residual stresses due to untempered core at the tip aided the micro-pitting and micro-cracking due to the rolling contact surface fatigue was responsible for the initiation of surface cracks and final failure of the gear.

Influence of Rolling Contact Surface and Contact Load on Fluctuation of Rolling Friction Force

This paper presents the experimental analysis for the fluctuation of rolling friction force, which deteriorates high precision motion in linear ball guideways. A simple drive with four tracks and four balls was used to investigate the influence of contact surface and contact load on the friction force fluctuation. To provide different surface integrity, ground, polished, and shot-peened surfaces were prepared. Experimental results showed that the friction force fluctuation was dependent on position change and influenced by the inclination angle of the rolling contact surface. The fluctuation of friction coefficient was inversely proportional to the cube root of the contact load. The wavelength analysis on the friction coefficient showed that friction coefficient was suppressed as the contact load increased. An empirical formula for estimating the friction force fluctuation was proposed based on these experimental results and a single ball friction model proposed by Ishikawa and Suda.

Prevention of Solidification of Al-40%Sn-1%Cu in Melt Pool on the Roll Casting Using Unequal Diameter Twin Roll Caster

Among the problems encountered when roll casting Al-405Sn-1%Cu, which is an aluminum alloy used for sliding plate bearings in large maritime diesel engines, are solidified chips embedded in the strip and scratch marks on the lower roll contact surface. In this study, three different improvement methods aimed at eliminating these particular defects—vibrating the side plates and back dam plate, adding a vibrating plate, and varying the casting conditions—are examined. Vibrating the side plates and dam plate was found to be effective for preventing these defects, while adding another vibrating plate was comparatively less effective. As for casting conditions, it was also determined that the occurrence of these defects could be reduced by increasing the roll speed, and that the molten metal casting temperature had little or no influence on defect formation.

Multiscale modeling and simulation of rolling contact fatigue

A hierarchical multiscale method is proposed in this paper to study the rolling contact fatigue with the consideration of lubricant effects. This multiscale model consists of a molecular model of lubricant and a continuum model of rolling contact components. At the nanoscale, molecular dynamics is employed to model the lubricant and to calculate the friction coefficient at the rolling contact surface. At the macroscale, the finite element method is used to conduct stress analysis of the rolling contact component so that the fatigue life can be predicted. The calculated friction coefficient is passed from the molecular model to the continuum model in the proposed multiscale model. The effect of fluctuating load on the rolling contact fatigue life is also studied in this paper. The objective of this paper is to develop a new multiscale framework which connects the nanoscale and the mascroscale. It shall be noted that a commonly used fatigue life model is employed in the continuum model.

Contact fatigue initiation and tensile surface stresses at a point asperity which passes an elastohydrodynamic contact

Abstract Contact mechanics and tribology was combined with fundamental fatigue and fracture mechanics to form a new mechanism for surface initiated rolling contact fatigue. Following, fatigue was investigated numerically for single asperities and craters in lubricated rolling contact surfaces. The hypothesis suggests that asperity point contacts can create sufficiently large tensile stresses for fatigue. The investigated case corresponded to a heavily loaded truck gear with ground surfaces. Reynolds equation resolved the elastohydrodynamic effect of the asperity in the transient three dimensional contacts. The Findley critical plane criterion was used for multiaxial and non-proportional fatigue evaluation. The simulations confirmed the new mechanism for rolling contact fatigue and showed how asperities can create contact fatigue in the lubricated contacts even without slip.

Analysis and Prediction of Defect Size and Remaining Useful Life of Thrust Ball Bearings: Modelling and Experiment Procedures

A new methodology based on full factorial design (FFD) for the prediction of the size of the spalls on the rolling contact surfaces of thrust ball bearings and its remaining useful life is presented in this research work. The FFD is used to analyse the effect of the following factors: rotational speed, load, spalling size, position of the sensors and frequency range on the vibrations level and the interaction effects between these factors. Data collected from vibratory signals generated by thrust ball bearings operating in the fatigue test rig are used. Statistical analyses show that the full factorial model with sixteen coefficients leads to more precise spalling size estimates. Analysis of variance showed that these results were statistically significant [P value is less than 0.0001 where significance level $$\alpha $$ ( $$\alpha = 0.05$$ )]. A modified exponential model used in the prediction of the remaining useful life shows its efficiency and applicability.

A Microscopic Observation of Rolling Contact Fatigue Damages under the Water-Contaminated Lubrication Environment

Rolling contact fatigue(RCF) is a major cause of failure that appears in components of rolling contacts. In the recent years, the fatigue propagation and failure have been an important issue in respect of the safe operation and to reduce the noise and vibration of the rolling contact components. The water-contaminated lubrication is known to be one of the significant factors that reduces the lifetime of the rolling contact components. Thus, in this study, the effect of water-contaminated lubrication environment on the rolling contact fatigue was investigated. Bearing life testing was performed in two different lubrication conditions (i.e. normal lubrication environment and water-contaminated lubrication environment). The effect of the debirs on the rolling contact fatigue could be eliminated by establishing the debris filter system. Microscopic features of the rolling contact surfaces were examined using energy dispersive spectrometry and non-contact 3D measurement system. In the case of the water-contaminated lubrication, the increase of surface roughness values up to 17.6% was observed. The oxidation state and pattern of the rolling contact surfaces were very different depending on the lubrication environment. It was also found that the bearing rating life, L10 , was decreased significantly in the watercontaminated lubrication condition. The amount of reduction was about 49.7%.