Dissertations / Theses on the topic 'Rolling Contact'
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1
Smith, Lindsey. "Rolling contact fatigue in wheel-rail contact." Thesis, University of Newcastle Upon Tyne, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.438385.
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Alshahrany, Shaya. "Rolling contact fatigue in heavily loaded gear transmission contacts." Thesis, Cardiff University, 2015. http://orca.cf.ac.uk/90422/.
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This thesis examines the influence of asperities such as found on the teeth of gears and discs, and failure mechanisms associated with rough surface Elastohydrodynamic Lubrication (EHL). The principal outcomes of the research provide a good insight into fatigue life, residual stress effects, damage prediction and surface contact failures. In particular, the study is intended to provide understanding into the residual stress distribution resulting from plastic deformation of surface asperities in the running in process. The residual stress is then added to the asperity elastic stress distribution and examined in detail to see the effects on fatigue damage and fatigue life. So, a theoretical model has been developed to assist design against the residual stress effect and surface contact fatigue, such as micropitting. The technique used in the study starts with developing an elastic plastic model of the rough surface by using the Abaqus Finite Element analysis software package. This is a nonlinear problem and ranges of applied loads have been applied to the as-manufactured surfaces causing the asperity features to experience varying degrees of plastic deformation. The pre and post running roughness profiles are studied in order to assess the level of plastic deformation actually occurring at significant surface asperity features by aligning the pre and post running profiles. This results in a new technique that has helped to identify the level of plastic deformation occurring in the practice, and also to make a comparison with FEA contact analysis for the same asperity features to identify the appropriate residual stress field. The residual stress field associated with the plastic deformation was extracted and evaluated. The extracted residual stress field was transferred to a form that facilitated IV inclusion in stress evaluation code to obtain the stress history for the material subject to loading in an EHL contact. The research carried out considers surface fatigue analysis with and without a residual stress field, so as to establish the influence of asperity plastic deformation on the fatigue properties of the surface. All the work is based on numerical simulation of surface fatigue failure in EHL situations and carried out numerically. The procedure can be applied quickly and gives the opportunity to apply several models and investigate the influence of all the model parameters on material deformation and fatigue life.
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Hadfield, Mark. "Rolling contact fatigue of ceramics." Thesis, Brunel University, 1993. http://bura.brunel.ac.uk/handle/2438/6622.
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Ceramic/ceramic and ceramic/steel contacts under lubricated rolling conditions are studied. This work is of interest to ball bearing manufacturers as the use of ceramics in the design of these components has some advantages over traditional bearing-steel materials. Low density and increased stiffness are the mechanical properties which gas-turbine and machine tool manufacturers are most likely to realise. Much research over the past two decades on material structure, quality control and manufacturing techniques has produced a material which can seriously challenge bearing steel in ball-bearing design. This is especially the case for hybrid ball-bearings, ie ceramic balls with steel bearing races which are now used as standard components. The purpose of this study is to examine the rolling contact fatigue failure modes of ceramics. This study concentrates on silicon nitride as this material has most potential for use by industry. The primary reason for studying ceramic balls is because of interest in ball-bearing applications, hence a modified four-ball machine is employed which correctly models ball motions and precisely defines ball load. Experimental and theoretical kinematic analysis of ball motion during modified four ball machine tests is presented. The kinematic analysis reveals that in practice, lower ball tracking exists at high speeds. Test conditions of lubricated contacts under high compressive stress show delamination type failures. Delamination failures are classified in terms of propagation and initiation from scanning electron microscope observations. Residual stresses are measured on delaminated surfaces, which implies plastic deformation of the ceramic. Also, chemical analysis implies that disruption of silicon, nitrogen and oxygen levels may take place on delaminated surfaces. Experiments illustrating various fatigue failure modes using artificially pre-cracked ceramic balls in contact with a steel upper ball are presented.
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Slocum, Alexander Henry Jr. "Rolling contact orthopaedic joint design." Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/81736.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2013.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references.
Arthroplasty, the practice of rebuilding diseased biological joints using engineering materials, is often used to treat severe arthritis of the knee and hip. Prosthetic joints have been created in a "biomimetic" manner to reconstruct the shape of the biological joint. We are at a disadvantage, however, in that metals and polymers used to replace bone and articular cartilage often wear out too soon, leading to significant morbidity. This thesis explores the use of kinetic-mimicry, instead of bio-mimicry, to design prosthetic rolling contact joints, including knee braces, limb prosthetics, and joint prostheses, with the intent of reducing morbidity and complications associated with joint/tissue failure. A deterministic approach to joint design is taken to elucidating six functional requirements for a prosthetic tibiofemoral joint based on anatomical observations of human knee kinetics and kinematics. Current prostheses have a high slide/roll ratio, resulting in unnecessary wear. A rolling contact joint, however, has a negligible slide/roll ratio; rolling contact prostheses would therefore be more efficient. A well-established four-bar linkage knee model, in a sagittal plane that encapsulates with the knee's flexion/extension degree of freedom, is used to link human anatomy to the shape of rolling cam surfaces. The first embodiment of the design is a flexure coupling-based joint for knee braces. Failure mode analysis, followed by cyclic failure testing, has shown that the prototype joint is extremely robust and withstood half a million cycles during the first round of tests. Lubrication in the joint is also considered: micro- and nano-textured porous coatings are investigated for their potential to support the formation of favorable lubrication regimes. Hydrodynamic lubrication is optimal, as two surfaces are separated by a fluid gap, thus mitigating wear. Preliminary results have shown that shear stress is reduced by more than 60% when a coating is combined with a shear thinning lubricant like synovial fluid. These coatings could be incorporated into existing joint prostheses to help mitigate wear in current technology. This thesis seeks to describe improvements to the design of prosthetic joints, both existing and future, with the intent of increasing the overall quality of care delivered to the patient.
by Alexander Henry Slocum, Jr.
Ph.D.
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Balcombe, Robbie. "A study of rolling contact fatigue cracks in lubricated contacts." Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/9848.
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A novel method for coupling fluid pressure and crack deformation for the purpose of analysing rolling contact fatigue (RCF) cracks in lubricated, hydrodynamic and elastohydrodynamic, contacts is presented. The model addresses some of the simplifying assumptions applied to existing models presented in the literature such as: (i) using an imposed fluid pressure gradient inside the crack, (ii) using an imposed fluid pressure at the crack mouth, and (iii) adopting a surface contact pressure, Hertzian or EHL, that does not account for the fluid flow in and out of the crack during loading. The model has been used to model the effect of lubricant/crack interaction in various RCF configurations as the rolling element passes over the pre-formed crack; which has direct application to bearings and rail/wheel contacts. The results of the simulations performed with the fully-coupled fluid/solid solver developed by the author suggest that the cracked component/lubricant interaction contributes significantly to accelerate the rate of surface breaking crack growth in rolling element bearings and wheel/rail type contacts. It is shown through simulations that the lubricant works as a catalyst inside the crack to convert the compressive contact load into a crack opening, tensile fatigue mechanism, through the effect of fluid pressurisation inside the crack. The results obtained using such a model suggest that the opening associated with the fluid action within the crack induces large mode I stress intensity factors. This has been shown to be the principal factor that promotes and influences the rate of rolling contact fatigue crack growth in lubricated contacts. In addition to the modelling work, an experimental method of analysing RCF cracks in real time has been developed. The technique is based on laser induced fluorescence that allows the penetration of the fluid within the crack to be observed. Though the method would require development to be used to provide results that could be used for quantitative comparisons with crack models, some encouraging preliminary results have been obtained: the technique has been shown to be suitable for measuring, at least qualitatively, the real time evolution of the film thickness in RCF cracks.
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Wang, W. "Rolling contact fatigue of silicon nitride." Thesis, Bournemouth University, 2010. http://eprints.bournemouth.ac.uk/17764/.
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Silicon Nitride has traditionally been used as rolling contact bearing material owing to its superior performance compared to bearing steels. Its successful application as a bearing element has led to the development of Silicon Nitride in other rolling contact applications in the automotive industry and the power industry. However, a major limitation of its wider application is its high material and machining cost, especially the cost associated with the finishing process. In the present study, a low cost sintered and reaction-bonded Silicon Nitride is used to study the surface machining effects on its rolling contact fatigue performance. Studies have been carried out to link the surface strengths of Silicon Nitride derived from half-rod and C-Sphere flexure strength specimens to the rolling contact lives of Silicon Nitride rod and ball specimens. The rolling contact fatigue tests were carried out on ball-on-rod and modified four-ball machines. Three types of surface with coarse, fine and RCF-conventional finishing conditions were examined. Flexure strength tests on half-rod and C-Sphere showed an increasing surface strength from specimens with coarse, fine to RCF-conventionally machined conditions. During rolling contact fatigue tests of as-machined specimens, no failures were observed on either ball-on-rod or four-ball tests after 100 million stress cycles. However, a trend of decreasing wear volumes was measured on the contact path of rods and balls with coarse, fine and RCF-conventional conditions. In four-ball tests, spall failures were observed on pre-cracked specimens. There was a trend of increasing rolling contact fatigue lifetime from pre-cracked specimens with coarse, fine to RCF-conventional machining conditions. The study of Silicon Nitride machining was also carried out using an eccentric lapping machine to investigate the effect of eccentricity on the finishing rate of hot isostatically-pressed and sintered and reaction-bonded Silicon Nitride. The eccentricity had no significant impact on finishing rate as concluded in this study. The effect of lubricant viscosity and chemistry on the rolling contact fatigue performance of Silicon Nitride was also studied. The result is inconclusive.
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Halverson, Peter Andrew. "Multi-stable Compliant Rolling-contact Elements." Diss., CLICK HERE for online access, 2007. http://contentdm.lib.byu.edu/ETD/image/etd1832.pdf.
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Everitt, Carl-Magnus. "Initiation of rolling contact fatigue from asperities in elastohydrodynamic lubricated contacts." Licentiate thesis, KTH, Hållfasthetslära (Avd.), 2018. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-222371.
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Rolling contacts are utilized in many technical applications, both in bearings and in the contact between gear teeth. These components are often highly loaded, which makes them susceptible to suffer from rolling contact fatigue. This work focuses on the rolling contact fatigue mechanism of pitting. In order to attain a better understanding of why pitting initiates and grows, detailed simulations of rolling contacts have been performed. In particular the contact between two gears in a truck retarder was here used as a case study. The investigated contact experienced elastohydrodynamic lubrication conditions since the load was high enough to causes the surfaces in contact to deform and the viscosity of the lubricant to increase significantly. In Paper A it was investigated if surface irregularities in the size of the surface roughness are large enough to cause surface initiated fatigue. The investigation focused on the pitch line since small surface initiated pits were found here even though there was no slip present. Since there were pits present at the pitch line, it is important that the theories of pitting can explain the development of pits also in the absence of slip. The conclusion of the work was that surface irregularities of the size of normal surface roughness are enough to cause surface initiated fatigue at the pitch line. In Paper B it was investigated why pits are more likely to initiate in the dedendum of pinion gears than in the addendum. In both areas slip is present but in different directions. In the dedendum the friction from slip is against the rolling direction which enhances the risk for pitting. The investigation was performed by studying the effect of the temperature rise in the contact caused by the slip. The conclusion drawn was that the temperature rise in the contact explained why pitting was more common in the dedendum than in the addendum.Rullande kontakter förekommer i många applikationer, till exempel i lager och mellan kugghjulständer. Både lager och kugghjul utsätts ofta för höga laster vilket gör att dess ytor löper stor risk att utmattas, vilket kallas rullande kontaktutmattning. Denna studie fokuserar på pitting, även kallat spalling, vilket är en typ av rullande kontaktutmattning där en utmattninsspricka växer fram som får delar av ytan att ramla av. För att få en bättre förståelse varför pittingskador uppkommer har noggranna simuleringar utförts av rullande kontakter. Kontakten mellan två tänder på kugghjul i en lastbilsretarder har används som underlag då många pittingskador påträffats på dem. För att minska friktionen och nötningen i kontakten mellan kuggtänderna användes smörjmedel. De höga lasterna lastbilsretardern utsattes för deformerade kuggarnas ytor elastiskt samtidigt de kraftigt ökade viskositeten hos smörjmedlet. Dessa förhållanden gör att kontakten kallas för elastohydrodynamiskt smord, vilket på engelska förkortas till EHL. I Artikel A undersöktes om små ytojämnheter kan orsaka ytinitierade pittingskador. Eftersom skadan påträffats i friktionslösa kontakter, så som vid rullcirkeln på de undersökta kugghjulen, är det viktigt att teorierna som förklarar uppkomsten inte är beroende av friktion. Undersökningen fokuserade därför på förhållandena vid rullcirkeln. Slutsatsen från arbetet var att små ytojämnheter, av samma storleksordning som ytojämnheterna på de undersökta kugghjulen, är tillräckligt stora för att orsaka utmattningsskador. I Artikel B undersöktes varför det är vanligare att pitts initieras i dedendum än addendum på drivande kugghjul. Kontakten på båda sidorna om rullcirkeln slirar svagt åt olika håll. Att kontakten slirar skapar friktion som är motriktad rullriktningen i dedendum vilket ökar risken för pittingskador. För att undersöka varför dessa förhållanden ökar risken för skador fördjupades analysen av kontakten genom att inkludera temperaturfältet. Simuleringarna visade att temperaturen ökar genom kontakten vilket orsakar en asymmetrisk spänningsfördelning. Denna asymmetriska spänningsfördelning gör att ytojämnheter i dedendum är troligare att orsaka skador än ytojämnheter i addendum.
QC 20180213
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楊貴永 and Kwai-wing Yeung. "Elastic-plastic analysis of rolling elliptical contacts and the effects of axial superimposed stresses on rolling contact fatiguefailure." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1987. http://hub.hku.hk/bib/B31231032.
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Yeung, Kwai-wing. "Elastic-plastic analysis of rolling elliptical contacts and the effects of axial superimposed stresses on rolling contact fatigue failure /." [Hong Kong] : University of Hong Kong, 1987. http://sunzi.lib.hku.hk/hkuto/record.jsp?B12333669.
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Hannes, Dave. "Growth of cracks at rolling contact fatigue." Thesis, KTH, Hållfasthetslära (Avd.), 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-33659.
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Rolling contact fatigue is a problem encountered with many machine elements.In the current report a numerical study has been performed in order to predictthe crack path and crack propagation cycles of a surface initiated rolling contactfatigue crack. The implementation of the contact problem is based on theasperity point load mechanism for rolling contact fatigue. The practical studiedproblem is gear contact. Different loading types and models are studied andcompared to an experimental spall profile. Good agreement has been observedconsidering short crack lengths with a distributed loading model using normalloads on the asperity and for the cylindrical contact and a tangential load on theasperity. Several different crack propagation criteria have been implemented inorder to verify the validity of the dominant mode I crack propagation assumption.Some general characteristics of rolling contact fatigue cracks have beenhighlighted. A quantitative parameter study of the implemented model hasbeen performed.Utmattning med rullande kontakter är ett ofta förekommande problem för många maskinelement. I den aktuella rapporten utfördes en numerisk studieför att förutsäga sprickvägen hos utmattningssprickor som initierats i ytan vidrullande kontakter. Implementeringen av kontaktproblemet bygger på asperitpunktlastmekanismen för rullande kontakter. Studien av kontaktproblemetär tillämpad till kugghjul. Olika belastningstyper och modeller studeradesoch jämfördes med profilen hos en experimentell spall. Bra överensstämmelseobserverades för korta spricklängder när en modell med fördelad belastninganvänds för en belastningstyp där en normalbelastning agerar på asperiten ochvid cylindriska kontakten och en tangentialbelastning införs på asperiten. Olikakriterier för spricktillväxt implementerades för att verifiera giltigheten av antagandetatt mode I spricktillväxt är dominant. Några generella kännetecken avutmattningssprickor med rullande kontakter framhävdes. En kvantitativ parameterstudie för den implementerade modellen utfördes.
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Hearle, Adrian Donald. "Deformation, shakedown and fatigue in rolling contact." Thesis, University of Cambridge, 1985. https://www.repository.cam.ac.uk/handle/1810/250858.
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Ahmed, Rehan. "Rolling contact fatigue of thermal spray coatings." Thesis, Brunel University, 1998. http://bura.brunel.ac.uk/handle/2438/5469.
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The practical advantages of thermal spray coatings like high deposition rates, low cost and tribological properties of high wear resistance have enabled these coatings to become an integral part of aircraft and automobile industry. Recent advancements in thermal spraying techniques like high particle speed and temperature call for new applications for these coatings. This experimental study addresses the Rolling Contact Fatigue performance of thermal spray coatings deposited by a variety of techniques like High Velocity Oxy-Fuel (HVOF), Detonation Gun (D-Gun) and Plasma spraying. RCF tests were conducted using a modified four ball machine in conventional steel ball bearing and hybrid ceramic bearing configurations. Tribological conditions during the RCF tests were varied by changing the test lubricant and the lubrication mechanism, contact load and shape of the drive coated rolling element to vary the roll/slip ratio. RCF tests were analyzed on the basis of the performance, coating failures using surface and subsurface observations, and residual stress studies. Experimental and theoretical studies of the ball kinematics have also been included. These tests revealed that the performance of the coated rolling elements was dependent upon the coating and the substrate properties. The coating thickness, substrate hardness, tribological conditions during the test, coating and substrate material as well as the coating process and the substrate preparation significantly affect the coating performance and the failure modes. Three different failure modes of these coatings have been discussed along with the changes in the near surface residual stress behaviour of the coated rolling elements.
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Lundberg, Oskar Erik. "Vibrations induced by surface roughness in nonlinear rolling contacts." Licentiate thesis, KTH, MWL Marcus Wallenberg Laboratoriet, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-155049.
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For efficient transportation in either trains, busses or passenger cars, rolling elements such as wheels, tyres, bearings and transmission elements are fundamental. The energy efficiency and the generation of noise and vibrations in rolling contacts depend on the surface roughness of contacting bodies. In order to optimize the surfaces of rolling elements, prediction of its impact on the dynamic response from rolling excitation is required. A computationally efficient method to include surface roughness in the modelling of rolling contacts is presented. More specifically, nonlinear effects on the contact force due to the threedimensional shape and roughness of the contacting surfaces are introduced in a moving point force formulation. As a consequence of the point force approximation follows the assumption that any dynamic wave motion within the contact area is negligible.The rolling contact force is nonlinear due to a varying relative displacement between contacting bodies and is therefore referred to as state-dependent. A study case for the state-dependent method consisting of a steel ball rolling on a steel beam showed good agreement between numerical predictions and measured beam vibrations. Furthermore, an application to the wheel-rail interaction show that roughness-induced contact nonlinearities have a significant impact on the dynamic response caused by rolling excitation.QC 20141103
ECO2 Vehicle Design
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JOSHI, PRASAD RAMAN. "AN ELASTIC CONTACT THEORY FOR MODELING VIBRATION TRANSMISSIBILITY THROUGH ROLLING CONTACT BEARINGS." University of Cincinnati / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1092882073.
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Olver, Andrew Vernon. "Wear of hard steel in lubricated, rolling contact." Thesis, Imperial College London, 1986. http://hdl.handle.net/10044/1/11466.
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Alwahdi, Farag Abdullah Mohamed. "Wear and rolling contact fatigue of ductile materials." Thesis, University of Sheffield, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.421003.
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Carroll, Robert Ian. "Surface metallurgy and rolling contact fatigue of rail." Thesis, University of Sheffield, 2006. http://etheses.whiterose.ac.uk/14639/.
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This thesis presents the results of an investigation into the effect of surface metallurgy on the rolling contact fatigue behaviour of rail. The investigation has used laboratory based rolling/sliding twin disc testing of samples with a surface metallurgical feature simulated on them. The samples used in laboratory testing have been compared with samples of rail removed from track. Two surface metallurgical features have been investigated: decarburisation and white etching layer. Decarburisation is the loss of carbon from the surface of the rail due to oxidation at high temperatures, resulting in a softer layer at the surface (180HV compared to 250HV bulk). The decarburised layer has been simulated in this research by heat treating discs in a laboratory furnace with an air atmosphere. The results show that by increasing the depth of decarburisation the growth rate of cracks within the sample, along with the wear rate, increases. At the maximum depth of decarburisation allowed on rail by the standard (O.5mm) there was little difference in the wear or rolling contact fatigue behaviour with or without decarburisation. White etching layer (WEL) forms on the surface of rail due to the action of the wheels and is a very hard layer (>850HV) up to 250mm deep. White etching layer has been simulated in two ways: spot welding and gross sliding of the discs. The results have shown that cracks initiate preferentially at weak spots at the surface, such as the interface between the WEL and pearlite or along proeutectoid ferrite boundaries. It has been found that the growth of cracks below the surface depends on the strain history of the subsurface pearlite. The results indicate that white etching layer is detrimental to rail life through either the promotion of rolling contact fatigue and/or wear.
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Sato, Meiji. "Wear and rolling contact fatigue of rail steels." The Ohio State University, 1991. http://rave.ohiolink.edu/etdc/view?acc_num=osu1335372747.
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Quiney, Zak. "Rolling contact fatigue detection via high frequency acoustic emission." Thesis, Swansea University, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.678470.
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Awan, Abdul Waheed. "Defect tolerance assessment of silicon nitride in rolling contact." Thesis, Bournemouth University, 2015. http://eprints.bournemouth.ac.uk/25044/.
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This thesis focuses on two relatively unexplored types of surface defects on silicon nitride balls – ‘star’ type defects and ‘missing material’. The main objective of this research is to determine failure modes and the critical or tolerable defect sizes for rolling bearing applications. This is achieved by means of both experimental and numerical techniques (for finding crack initiation location). A modified four-ball machine is used for the rolling contact fatigue experiments on star features and missing material defects (both during manufacturing process and artificially produced) on the surface of silicon nitride balls. Experiments are conducted at different loads (3.8-4.8GPa), lubrication types, specific speed (7500rpm) and temperature conditions (75°C) to find rolling contact fatigue limitations in relation to these defects. Laser micromachining is used to produce precise holes and trenches to simulate missing material. Two different types of bearing grade silicon nitride are tested to determine tolerance and failure modes in rolling contact fatigue. Scanning electron microscopy, light microscopy and white light interferometry are used for surface analysis and topography. Post-experiment analysis in the star feature experiments has shown that star like radial cracks are prone to develop into missing material by internal fracture over the extent of the star in lubricated rolling contact. Lubrication quality or film thickness and orientation of the pre-existing cracks to the rolling direction influenced the damage process and severity. In the case of missing material experiments, samples with different diameters (50-100μm), depths (5-50μm) and shape (right cylindrical, conical and oblique cylindrical) were tested. It has been confirmed that, apart from the main experimental parameters like applied pressure, cavity diameter and depth, parameters such as cavity base profile, shape and cavity location and orientation on the contact track are important for rolling contact fatigue of silicon nitride material. Replica produced cavity base profiles to investigate failure reasons. Cross-sectioning also gave very good insight of surface and subsurface features both before and after testing (including un-failed specimens). Incipient spalls on tested samples provided the information to understand the failure mechanism (mainly spalling) in the material. FEM is used for finding stress fields at surface and sub-surface positions and ultimately predicting the location and position of crack initiation. 2D (Axi-symmetric and plane strain) and 3D models are developed to compare the results, whereas static versus quasi static analysis is presented to examine the effect of rolling. Models are verified using classical contact theory. Hydrostatic pressure effects are also successfully modeled using the finite element analysis approach. Fluid elements modeling on the solid interface of the cavity produced a different stress field and have indicated the location of crack initiation.
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Qiu, Xiaonong. "Rolling contact fatigue behavior of three eutectoid rail steels /." Full text open access at:, 1987. http://content.ohsu.edu/u?/etd,153.
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Kim, Tae Hyun. "Fatigue of surface engineered steel in rolling-sliding contact." Thesis, Imperial College London, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.325019.
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Al-Sabti, Sara Louise. "Failure modes of polymethylmethacrylate resulting from rolling line contact." Thesis, Brunel University, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.311264.
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Yang, Yulin. "Evaluation of rolling contact fatigue resistance for coated components." Thesis, University of Hull, 2003. http://hydra.hull.ac.uk/resources/hull:8534.
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The thesis reviews and studies current evaluation mechanisms, techniques and machines for testing rolling contact fatigue failure resistance and load capacity of coated components. The thesis investigates both normal and accelerated rolling contact fatigue evaluation test mechanisms and their models, and evaluation test technique principles suitable to the appraisal of coated bearing components. A major contribution of the thesis is the design and development of a new rolling contact fatigue evaluation test machine for coated components. Tests of the rolling contact fatigue of coated bearing raceways under the oil lubricant, grease lubricant and no lubricant conditions, applying the new rolling contact fatigue evaluation mechanisms, evaluation technique principles and the new test machine, have been performed. The accelerated rolling contact fatigue tests of the coated bearing raceways use SiC powder in the oil lubricant. The new rolling contact fatigue test machine has been found suitable for evaluating the rolling contact fatigue resistance of components with superhard coatings. The accelerated rolling contact fatigue test method has been shown to give comparable rolling contact fatigue test results to those obtained in a normal rolling contact fatigue test, while being much faster. In the fatigue test, the cyclic maximum shear stress produces an initial fatigue crack near the substrate surface of the test bearing raceways. The observed phenomena are consistent with theory, although the location of the initial crack is much closer to the surface than would be predicted by a 'static' Hertzian analysis. Insufficient traction forces on the contact surface between the rolling elements of a test coated bearing makes gross skidding occur, leading to rapid wear, over-heating and final failure of the test coated bearing. The LSO fatigue life of the test coated bearing raceway tends to decrease with increase of the coating thickness and coating hardness of the test coated bearing raceway.
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Fish, Gareth. "The effect of emulsion chemistry on rolling contact fatigue." Thesis, Imperial College London, 1990. http://hdl.handle.net/10044/1/46297.
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Fu, Hanwei. "Microstructural alterations in bearing steels under rolling contact fatigue." Thesis, University of Cambridge, 2017. https://www.repository.cam.ac.uk/handle/1810/270311.
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The formation of microstructural alterations in bearing steels under rolling contact fatigue (RCF) is systematically studied. A literature review summarizes current understanding in this field, leading to the key to the formation of these microstructural features being carbon redistribution as a consequence of cyclic rolling contact. In this context, a novel theory is postulated to describe the migration of carbon caused by gliding dislocations. The theory combines the Cottrell atmosphere theory with the Orowan equation and is capable of quantifying the dislocation-assisted carbon flux. Based on the proposed theory, models are suggested for different types of microstructural alterations formed in rolling contact fatigued bearings – dark etching regions (DERs), white etching bands (WEBs) and white etching areas (WEAs). Very good agreement is obtained between the predications made by the models and the experimental data from both this research and the literature. Moreover, the models consider the effects of contact pressure, temperature, rotational speed and number of cycles, and thus can be applied for universal RCF testing conditions. The reproduced microstructural features are also characterized using advanced characterization techniques such as scanning electron microscopy (SEM), transmission electron microscopy (TEM) and atom probe tomography (APT), with the observation validating the postulated formation mechanisms. It is demonstrated that DERs, WEBs and WEAs follow the same principle during formation – strain induced carbon redistribution. This is the first time that these microstructural alterations are quantitatively described using a unified theory. The achievements obtained from this research can be far reaching. It not only leads to great progress in understanding the phenomenology of RCF in bearing steels, but also can be further extended to other scenarios with similar phenomena such as severe plastic deformation and hydrogen embrittlement.
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Ghaffari, Gharehbagh Mir Ali. "Multi-scale modeling and simulation of rolling contact fatigue." Diss., University of Iowa, 2016. https://ir.uiowa.edu/etd/2082.
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In this thesis, a hierarchical multiscale method was developed to predict rolling contact fatigue lives of mechanical systems. In the proposed multiscale method, the molecular modeling and simulation of lubricant was conducted to investigate the friction between rolling contact surfaces. The calculated friction coefficient was passed to the continuum model of rolling contact components to predict fatigue lives.
Molecular dynamics modeling and simulation of thin film lubrication and lubricated contact surfaces were carried out to investigate mechanisms of hydrodynamic lubrication at nano-scale first. Although various lubricant alkane chains were considered in the molecular model, the chain length of eight united molecules were mainly employed in this thesis. In addition, the effects of temperature and nano-particles (debris) on the friction forces were discussed. It was found that the existing of nano-particles (debris) could increase the friction force between contact surfaces with hydrodynamic lubrication.
In the continuum model of the developed multiscale method, finite element analysis was employed to predict rolling contact fatigue life of rolling contact components, including bearing and gear-tooth. Specifically, the fatigue crack initiation of bearing was studied, and then the fatigue crack initiation and propagation in gear-tooth. In addition, the enhancement of gear-tooth fatigue life by using composite patches was discussed as well. It should be noted that the friction coefficient used in the continuum model was calculated in the molecular model. It is one-way message passing in the developed multiscale method.
Another continuum method was studied and developed in this thesis to provide alternate methods for the continuum model in the proposed multiscale framework. Peridynamics method has advantages in modeling and simulation of discontinuities, including cracks, over the conventional finite element methods. The applications of Peridynamics in predicting fatigue crack initiation and propagation lives were discussed in this thesis.
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Nilsson, Rickard. "On wear in rolling/sliding contacts." Doctoral thesis, KTH, Machine Design (Div.), 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-122.
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The aim of this thesis is to increase the understanding of wear in rolling/sliding contacts such as the wheel-rail contact for railroads and the roller-washer contact for roller bearings.
The Stockholm commuter train network has been the subject of papers A and B in this thesis in which the wear and surface cracks on rails has been observed for a period of three years. By comparing the wear depth with the crack length, equilibrium between these two damage mechanisms was found for a lubricated rail. By using a lubricant with friction modifiers the stresses was low enough to prevent crack propagation; at the same time, the rail was hard enough to reduce the wear rate. This is probably the most favourable state in terms of rail maintenance cost.
Roller bearings subjected to lubricant borne particles have been the subject of papers C, D and E in this thesis. Particles in the lubricating oil can have a significant impact on the wear in lubricated contacts. Even at low concentration levels can self-generated particles cause significant wear. The here presented results shows that filtration during run-in can significantly reduce both the mass loss and the number of self generated particles. A series of experiments has been carried out to study the wear of roller bearings by ingested lubricant borne hard particles. The form of the worn profile and the length of wear scratches correspond closely to the sliding within the contact. A count of the number of wear scratches on the rolling element surface indicates that the contact concentrates particles. A novel wear model based on the observation of a single point on the contacting surface when a concentration of particles passes through it has been developed and the necessary data for the model has been determined from the experiments. Comparison of the simulation results with the experimental results shows good qualitative agreement for the form change of the washer surfaces.
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Liu, Gavin Chunye. "Vibration analysis of a thin moving web and its finite element implementation /." Online version of thesis, 1992. http://hdl.handle.net/1850/10698.
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Dahlberg, Johan. "On the asperity point load mechanism for rolling contact fatigue." Doctoral thesis, Stockholm : Hållfasthetslära, Kungliga Tekniska högskolan, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4569.
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Stewart, Simon Hardie. "The rolling contact fatigue of post-treated thermal spray coatings." Thesis, Heriot-Watt University, 2005. http://hdl.handle.net/10399/234.
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Iida, Yusuke. "The effects of magnetic fields on rolling contact fatigue wear." Thesis, Brunel University, 2007. http://bura.brunel.ac.uk/handle/2438/7405.
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The thesis describes the effects of the magnetic field in rolling contact tests of steel by using a two-disc machine and the investigation of its mechanism from contact stress analysis by using FEM and the agnetisation of a ferromagnetic substance. In the tests, two contact kinematic conditions, that is pure rolling and 10% rolling with sliding together with 1.1 and OAT [Tesla] of horizontal static magnetic fields created by permanent magnets were pplied. The results of optical and scanning electron microscopy observations show that finer wear particles and smoother worn surfaces are produced in the presence of the magnetic field. For the generation of the finer wear particles, it is considered necessary that the subsurface crack initiation point is moved towards the surface due to the magnetic field. Wear amounts of the discs are lowered III the magnetic fields under the pure rolling conditions. However, at 100/0 rolling with sliding, the wear amounts are increased in the magnetic fields even though finer particles and smoother surfaces are observed. Both tendencies are unified by calculating the number of cycles required to generate wear particles, which are reduced due to the magnetic field's presence. For these mechanisms, it is considered that domain walls near the contact region are caught by dislocations when the specimen is agnetised and part of the energy for magnetisation activates the dislocation movement resulting in crack initiation.
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Khan, Zulfiqar Ahmad. "Rolling contact wear of hybrid ceramic bearings with refrigerant lubrication." Thesis, Bournemouth University, 2006. http://eprints.bournemouth.ac.uk/10064/.
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Silicon nitride Si3N4 bearing elements have shown practical advantages over traditional steel elements due to their mechanical and physical properties. Leading technology and demands for high efficiency have caused loading bearing contacts in all kinds of machinery to be subjected to high speeds, high contact stresses and severe conditions of lubrication. In addition the introduction of a new generation of hydrocarbon refrigerants in various systems, where these rolling contact silicon nitride bearing elements are employed raises further demands to evaluate the rolling contact fatigue performance of these elements with refrigerant lubrication. Obtaining material wear properties of these refrigerants used in mechanical applications is difficult due to high saturation pressure of the refrigerants. It is important to investigate the influence of these refrigerants as lubricants on the rolling contact fatigue performance of ceramic bearing elements. This research responds to the need for bench testing of rolling contacts using the new generation refrigerants as lubricants. A novel pressurised chamber was designed to achieve a liquid state of the refrigerant as fluid for the rolling contact fatigue experiments. A high-speed rotary Tribometer was used for rolling contact fatigue tests. Experimental study of the influence of the liquid refrigerant lubrication on rolling contact wear of the silicon nitride/steel elements is presented. Investigations of the lubricated contact of silicon nitride rolling elements using the pressurised chamber reveal that wear rate is affected by the nature and geometry ofthe induced defect. A residual stress survey was also performed on failed ceramic elements. Analysing the relationship of residual stress with rolling contact fatigue is an important study which will provide guidelines on the design process and manufacturing of these elements. The residual stress field analysis shows that residual stresses are relieved due to sub-surface damage and are inversely related to stress cycles. Maximum tensile stresses at the edges of the contact path cause a weaker residual stress field at the sub-surface crack front.
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Kapoor, A. "Geometry changes and crack initiation in rolling and sliding contact." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.234987.
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Lundberg, Oskar. "On the influence of surface roughness on rolling contact forces." Doctoral thesis, KTH, MWL Marcus Wallenberg Laboratoriet, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-193935.
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Road vehicle tyres, railway wheels and ball bearings all generate rolling contact forces which are transferred within a finite area of contact between the rolling element and the substrate. Either it is visible or not for the human eye, a certain degree of roughness is always present on the contacting surfaces and it influences the generation of both vertical and lateral contactforces. The purpose of this investigation is to enhance the understanding and modelling of the influence from small-scale surface roughness on the generation of rolling contact forces. To this end, a computationally efficient method to include roughness-induced contact nonlinearities in the dynamic modelling of rolling contacts is proposed. The method is implemented in a time domain model for vertical wheel–track interaction to model rolling-induced rail vibrations, showing good agreement with measurements. Furthermore, a test rig is developed and used for the investigation of tyre–road rolling contact forces. Detailed studies are performed on the influence of substrate roughness on the resulting contact forces for a tyre tread block which is rolling at different operating conditions. The choice of substrate as well as the rolling velocity and the slip ratio is observed to have significant influence on the resulting friction coefficient. For high slip ratios, stick–slip oscillations appear, exhibiting frequency content which is largely dependent on the choice of substrate. The outcomes of this study can potentially be used to improve future tyre–road contacts with respect to wear, traction and noise generation.QC 20161013
Centre for Eco2 Vehicle Design
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Hanzal, Robert J. F. "Rolling contact fatigue failures in silicon nitride and their detection." Thesis, University of Southampton, 2013. https://eprints.soton.ac.uk/361698/.
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The project investigates the feasibility of using sensor-based detection and processing systems to provide a reliable means of monitoring rolling contact fatigue (RCF) wear failures of silicon nitride in hybrid bearings. To fulfil this investigation, a decision was made early in the project to perform a series of hybrid rolling wear tests using a twin disc machine modified for use on hybrid bearing elements. The initial part of the thesis reviews the current understanding of the general wear mechanisms and RCF with a specific focus to determine the appropriate methods for their detection in hybrid bearings. The study focusses on vibration, electrostatic and acoustic emission (AE) techniques and reviews their associated sensing technologies currently deployed with a view of adapting them for use in hybrids. To provide a basis for the adaptation, an understanding of the current sensor data enhancement and feature extraction methods is presented based on a literature review. The second part describes the test equipment, its modifications and instrumentation required to capture and process the vibration, electrostatic and AE signals generated in hybrid elements. These were identified in an initial feasibility test performed on a standard twin disc machine. After a detailed description of the resulting equipment, the thesis describes the calibration tests aimed to provide base data for the development of the signal processing methods. The development of the signal processing techniques is described in detail for each of the sensor types. Time synchronous averaging (TSA) technique is used to identify the location of the signal sources along the surfaces of the specimens and the signals are enhanced by additional filtering techniques. The next part of the thesis describes the main hybrid rolling wear tests; it details the selection of the run parameters and the samples seeded with surface cracks to cover a variety of situations, the method of execution of each test run, and the techniques to analyse the results. The research establishes that two RCF fault types are produced in the silicon nitride rolling element reflecting essentially different mechanisms in their distinct and separate development; i) cracks, progressing into depth and denoted in this study as C-/Ring crack Complex (CRC) and ii) Flaking, progressing primarily on the surface by spalls. Additionally and not reported in the literature, an advanced stage of the CRC fault type composed of multiple and extensive c-cracks is interpreted as the result of in duced sliding in these runs. In general, having reached an advanced stage, both CRC and Flaking faults produce significant wear in the steel counterface through abrasion, plastic deformation or 3-body abrasion in at least three possible ways, all of which are described in details.
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Evans, M. H. "White structure flaking failure in bearings under rolling contact fatigue." Thesis, University of Southampton, 2013. https://eprints.soton.ac.uk/355966/.
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White structure flaking (WSF) as a premature wear failure mode in steel rolling element bearings is caused by white etching cracks (WECs) and perhaps butterflies formed in the ~1 mm zone beneath the contact surface under rolling contact fatigue (RCF). WECs are branching crack systems typically several millimetres in length that have a microstructural change called ‘white etching area’ (WEA) associated with the crack. Butterflies are smaller cracks initiating at material defects and impurities that form WEA wings that revolve around their initiators. Hydrogen diffusion into the bearing steel during service and transient operating conditions have been suggested as drivers of white etching features (butterflies, WEA and WECs). However the initiation and propagation mechanisms as well as the thresholds for WEC formation are not well understood. This is due to the difficulties of creating WECs repeatedly under laboratory conditions and the lack of a method established for mapping WECs in detail or 3 dimensions as typically only limited metallographic analyses are conducted over several cross-sections. A series of RCF tests have been conducted in this study to investigate the formation drivers and formation mechanisms of WECs using a two-roller RCF machine. WECs were successfully created in hydrogen charged 100Cr6 martensitic steel rollers under low-moderate concentrations of diffusible hydrogen (~1 ppm) and service realistic loading conditions (Pmax 1.5 – 2 GPa). However, only butterflies were formed under transient conditions with non-hydrogen charged rollers. One such butterfly was analysed in detail to further understanding of crack formation mechanisms and carbide dissolution as part of the WEA microstructural change. Based on the evidence obtained from the SEM, FIB tomography and STEM/TEM analysis, a void/cavity coalescence theory for initial butterfly crack formation and iron chromium carbide dissolution as part of the WEA formation mechanism is proposed. Metallography was extensively used in this project to view cross-sections of the wear zones subject to RCF. A metallographic serial sectioning technique was established to quantitatively map wear zones for the first time. Mapping WECs in their entirety and 3D modelling revealed the 3-dimensional morphology and orientation of WECs and maximised detection of possible WEC initiators. This study has for the first time quantitatively investigated the influence of diffusible hydrogen, load and rolling cycles on white etching feature formation and the thresholds of formation. The hydrogen charged tests showed that the formation of butterflies was independent of the concentration of diffusible hydrogen with the test parameters used, but dependent on contact pressure and number of rolling cycles up to a threshold. WEC formation thresholds were found at certain values of the concentration of diffusible hydrogen, contact pressure and number of rolling cycles. Extensive serial sectioning and 3D modelling of WECs also demonstrated that the orientation of WECs differed depending on the sectioning direction. It was found that the vast majority of WECs were contained in the subsurface wear zone and did not make any connection with the surface, thus dismissing surface initiation. The WECs often interacted with inclusions that were judged to be crack initiators and evidence was found that butterfly cracks could propagate to form WECs. The white etching features initiated predominately at short sulfide type inclusions, small globular manganese sulfide oxide inclusions and small globular oxide inclusions. Therefore strong evidence was observed for a subsurface initiation mechanism of WECs from non-metallic inclusions. A comparison of the WEC formations in the hydrogen charged two-roller tests was made with serial sectioning investigations of WEC formation in wind turbine gearbox bearings obtained from the field and those tested on a large-scale transient test rig (non-hydrogen charged). This was performed to understand if a difference in the WEC initiation and propagation mechanism occurs under the differing conditions. The comparison showed correlation between the WEC formation mechanisms as a high number of inclusions interacted with the WECs that were judged to be crack initiators and small/short sized inclusions predominated as the crack initiators. Therefore based on the serial sectioning analysis across various test specimens and bearings it is proposed that one mechanism of WEC formation is due to multiple linking of extended butterflies or small WECs in the subsurface to form larger WEC networks that eventually propagate to the surface resulting in WSF. The data also suggests that steel cleanliness standards analysing inclusion density (as opposed to maximum inclusion lengths) are more relevant in understanding butterfly/WEC initiation. However steel cleanliness standards used should record inclusions that are only a couple of micrometer’s in length/diameter.
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Li, Yawei. "Dynamic prognostics of rolling element bearing condition." Diss., Georgia Institute of Technology, 1999. http://hdl.handle.net/1853/15847.
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Mutyala, Kalyan Chakravarthi. "Influence of Metallic, Dichalcogenide, and Nanocomposite Tribological Thin Films on The Rolling Contact Performance of Spherical Rolling Elements." University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1447751680.
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Kang, JeeHyun. "Mechanisms of microstructural damage during rolling contact fatigue of bearing steels." Thesis, University of Cambridge, 2014. https://www.repository.cam.ac.uk/handle/1810/245255.
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Bearings are employed in a number of applications under extremely demanding conditions. During long operation times, the material undergoes rolling contact fatigue where microstructural damage manifests as dark-etching regions and white-etching areas, which display different properties from the surrounding region. The aim of this study is to identify the mechanisms for such damage and to suggest models that can explain the influence of the initial microstructure and test conditions. In order to appraise the stress state in rolling contacts, two testing techniques were employed and it was examined if the testing methods could reproduce the same damage as in bearing operation. During ball-on-rod fatigue testing, microcracks were generated adjacent to inclusions and some were decorated with white-etching areas. Repetitive push tests showed a similar extent of subsurface hardening compared to the ball-on-rod tests, and allowed the strain per stress cycle to be measured. The microstructural alterations in a white-etching area were studied both on a macroscale and on an atomic-scale. The degree of stress concentration near a microcrack was calculated employing a nite element method. The microstructure, as well as the segregation behaviour of alloying elements in the white-etching area, were investigated by employing transmission electron microscopy and atom probe tomography. A nanocrystalline structure with scattered carbide particles was observed in the white-etching area. Carbon and silicon segregation was highly pronounced in some boundaries of dislocation cell structures. Models were suggested to account for the microstructural alterations during rolling contact fatigue. Carbide coarsening in dark-etching regions was modelled by considering how carbon di usion is assisted by dislocation glide. The predicted hardness evolution was consistent with experimental observation. The kinetics of carbide dissolution in white-etching areas was calculated by taking two processes into account: deformation accumulation and carbon diffusion. These models suggest that the microstructural changes during bearing operation can be controlled by tailoring the initial microstructure and managing the test conditions.
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Chertok, Daniel. "Hysteretic friction in the transient rolling contact problem of linear viscoelasticity." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1998. http://www.collectionscanada.ca/obj/s4/f2/dsk2/tape15/PQDD_0001/NQ37689.pdf.
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Tyfour, Wa'il Radwan Ali. "Interaction between wear and rolling contact fatigue in pearlitic rail steels." Thesis, University of Leicester, 1995. http://hdl.handle.net/2381/34715.
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The work presented in this thesis is aimed at investigating the interaction between wear and rolling contact fatigue, which are two of the most serious forms of deterioration caused by the wheel on rail contact stresses. Wheel-rail contact conditions were simulated by a two disc contact using the LEROS (LEicester university ROlling-Sliding wear testing machine). Investigation of the wear behaviour of BS11 pearlitic rail steel showed that steady state wear behaviour is established after a certain number of rolling-sliding cycles. Contact surface failure by ratchetting (accumulation of unidirectional plastic strain) was found to be the dominant failure mechanism during the period leading to the steady state. This mechanism was confirmed by the drop in the wear rates when the direction of rolling-sliding; i.e. strain in the surface layer, was reversed at predetermined numbers of cycles. The effect of repeated rolling direction reversals on crack morphology, propagation and rolling contact fatigue (RCF) life of BS11 rail steel was also investigated. It was established that rolling direction reversal has a beneficial effect on RCF life. A new mechanism, the "variable crack face friction mechanism", was proposed to explain this effect. Interaction between wear and RCF fatigue was investigated through rolling-sliding experiments where specimens were run dry for certain number of cycles, to induce different levels of wear damage, before the fatigue performance was investigated. It was shown that initial dry cycles above a critical number causes sudden and significant deterioration in RCF life. This deterioration has been explained in terms of the role of the accumulation unidirectional plastic strain (ratchetting) in initiating and propagating the early cracks during the dry phase. A strong correlation was found between the total ratchetting strain induced during the dry phase and the deterioration in RCF life. An empirical relationship to estimate this deterioration was concluded.
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Nygaard, James Robert. "Understanding the behaviour of aircraft bearing steels under rolling contact loading." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709284.
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Chen, Yong Kang. "Tribology of polymers and composites in unlubricated rolling and sliding contact." Thesis, University of Birmingham, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.629939.
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A reliable and simple twin-disc test rig has been designed and built and used for rolling-sliding tests. The real-time measurement system has allowed a detailed study of tribological behaviour of polymers and reinforced polymer composites under unlubricated, non-conformal and rolling-sliding contact. A mathematical model has been established to enable the disc surface temperature to be predicted. Both polyoxymethylene, polyamide 66 and short glass-fibre reinforced polyamide 66 composites have been investigated in the present work. A comprehensive set of results has been obtained for polyoxymethylene over a range of slip ratios, loads and speeds, and for polyamide 66 and short glass fibre reinforced polyamide 66 composites over a range of slip ratios and loads with a constant speed. This experimental information has revealed major differences in tribological behaviour between these materials. The predominant wear mechanisms were studied by surface and subsurface analysis and surface temperature characterisation. An attempt to apply the current results to engineering components made from these materials has been made. It is shown that friction-generated heat has a major influence on the performance of unreinforced POM and PA 66. The maximum surface temperature when these materials are in contact dominates their wear transitions. An attempt to establish an envelope for engineering applications has been made. POM appears to exhibit better wear resistance than P A 66 which was always inferior with higher wear rates and a tendency to form deep cracks in the surface. Experimental results show that the tribological behaviour of short glass-fibre reinforced polyamide 66 composites can be improved significantly by changing the crystallinity of the materials. The effects of moulding conditions have been investigated. The key is a thin film which exists on the contact surfaces when two discs run against each other under these test conditions. The film plays a dominant role in the "self-lubricating" property of the composite.
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Karunamurthy, Balamurugan. "Erosion and rolling contact wear mechanisms in silicon nitride hybrid bearings." Thesis, Bournemouth University, 2009. http://eprints.bournemouth.ac.uk/16062/.
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One remarkable advantage of hybrid bearings over all steel bearings is the elimination of separate oil lubricant system in applications, such as compressors and pumps in refrigeration and air conditioning units. High speed test runs restricted increase in speed due to material wear, which eventually affected the life of bearings. Being low saturation temperature fluids, change of phase is very common in refrigerants and cryogenic liquids, which lead to cavitation. Silicon nitride rolling elements with different sintering additives, properties and microstructure were experimentally studied to understand the nature of cavitation erosion. Advanced surface analysis technique was used study the erosive wear correlation to microstructure of test materials. Cavitation erosion wear initiated by multiple intergranular and transgranular fracture, leading to erosion pit formation. Grain size and grain boundary composition have shown to be the dominant factors for providing resistance to cavitation. Effect of surface defects and lubricant viscosity on cavitation erosion was investigated and is detailed in this thesis. A rotary specimen method was designed to study the effect of cavitation on rolling bodies. Computational modelling of acoustically generated cavitation was attempted and is also reported in this work. A novel test methodology was designed and manufactured by modifying a rotary tribometer to allow controlled experimental testing of two different phenomena rolling contact fatigue and cavitation erosion. This testing made it possible to study rolling and erosive wear mechanisms of rolling elements. Cavitation created far away in this new system is shown to be transported to the rolling contacts. The mechanism of material damage was by surface weakening due to mechanical impact of bubbles, which enhance fluid entrance and hydrodynamic pressure leading to wear initiation. Micro erosion pits formed in the rolling contact, which accelerated the damage by dislodging grains and bunch of grains. This testing method is suitable for a qualitative assessment of cavitation-RCF damage for different fluids with varying viscosities, and operating conditions.
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Frolish, Michael Fraser. "Design criteria for rolling contact fatigue resistance in back-up rolls." Thesis, University of Sheffield, 2002. http://etheses.whiterose.ac.uk/15083/.
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The demands placed on back-up rolls in hot strip mills have been investigated by a combination of literature and industrial studies. The tribological operating conditions have been established and the maximum local loads and pressure distributions at the work roll/back-up roll interface have been obtained by processing mill and roll schedule data using a computer program (commercial software developed by V AI Industries (UK) Ltd) and applying the theories of contact mechanics. After a study of the responses of the rolls to these demands and possible failure mechanisms, research has centred on surface initiated damage whereby cracks can propagate into the roll substrate potentially reaching the internal residual stress fields and leading to catastrophic failure. A proposed qualitative contact and fracture mechanics model, for the rolling contact fatigue and spalling failure, has been quantified theoretically using published methods for determining the stress intensity factors at the tips of pressurised and water lubricated, inclined rolling contact fatigue cracks. The predictions of the quantitative model in terms of crack directions and lengths have been validated by microscopic observation of the morphologies cracks produced in test discs used in the "SUROS" Rolling-Sliding Testing Machine and also in a sample of material spalled from a back-up roll. The quantitative failure model includes criteria for crack branching either upwards leading to micro spalling or downwards (potentially catastrophic) and the link between these two cases has been related quantitatively to the value of the mode I threshold for the roll material. After linking mechanics to microstructure and quantifying the interactions between wear and rolling contact fatigue in this case, practical quantitative recommendations have been made for the design of bainitic back-up roll materials, back-up roll redressing procedures and the surface roughness of both the work rolls and back-up rolls presented to the mill.
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Rycerz, Pawel. "Propagation of surface initiated rolling contact fatigue cracks in bearing steel." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/44525.
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The useful life of mechanical components which experience highly stressed rolling/sliding contacts, such as rolling element bearings or gears, is limited by rolling contact fatigue (RCF). Surface initiated pitting is a mode of RCF which has in recent years received particular attention from industry due to its frequent occurrence in service. This work focuses on the growth behaviour of RCF cracks before they develop into surface pits. A three-contact disc machine was used to perform pitting experiments on bearing steel samples. Preliminary tests showed that surface initiated cracks could be reproduced under high contact pressure and mixed lubrication regime. However, it was not possible to detect them using the vibration monitoring system installed on the test rig. This led to the development of a high sensitivity crack detection system which employs the principle of magnetic flux leakage (MFL). The existing test rig was modified to accommodate an inductive sensor and required signal acquisition electronics. In addition, a signal processing procedure was developed to enable analysis in real time. It was shown that the MFL technique is significantly more sensitive than commonly used alternatives. The system is capable of automatically finding cracks down to about 100 μm in length. In addition, results have shown a linear relationship between defect size and signal amplitude which enables in-situ sizing of cracks. Using the crack detector, a procedure to generate cracks and extract their growth rates was established. Crack growth was first studied under high contact pressure. It was found that initiation occurred very early in total life, which was attributed to high asperity stresses due to mixed lubrication regime. Total life to pitting was dominated by crack propagation, the speed of which was shown to depend on crack size. Small cracks grew at a steady and slightly decreasing rate until a critical size is reached at which propagation speed rapidly increases, shortly followed by pitting. Further study at lower loads confirmed that contact pressure is the main parameter controlling propagation speed. In order to identify a suitable crack propagation law, the measured crack growth rates were plotted against a stress intensity parameter expressed in terms of maximum contact pressure and crack size. The results suggest that after reaching certain length, rolling contact fatigue cracks grow according to a Paris-type power law, where the exponent of stress intensity parameter, and therefore contact pressure, was found to be approximately 7.5.
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Williams, Tracy Denise. "Remote condition monitoring of rolling element bearings with natural crack development." Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/17243.
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Pärssinen, Mikael. "Studies on dynamic response caused by contact between rough surfaces." Doctoral thesis, KTH, Vehicle Engineering, 2001. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3196.
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