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Hasan, Abdullah Mohammed. "Quantitative Laser-based Assessment of Top of Rail Friction Modifiers for Railroad Application." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/70916.
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The primary purpose of this study is to assess the effectiveness and utility of laser-based sensors for measuring, quantitatively, the presence and extent of top-of-rail (TOR) friction modifiers that are commonly used in the railroad industry for reducing friction between railcar wheels and rail. Modifying the friction between the wheel and rail is not only important for significantly reducing rolling resistance, but it also contributes to reducing wheel and rail wear, lowering rolling contact fatigue, and potentially curving resistance. It is common to monitor rail lubrication empirically by manually observing the sheen of the rail and tactically sensing any residues that may be present on the rail. Often performed by experienced railroad engineers, such methods are highly subjective and do not provide a quantitative assessment of how lubricated or unlubricated the track may be.
A new, quantitative measurement method for accurately assessing the state of lubrication of rail is developed and studied in depth. The method takes advantage of the light reflection and dispersion properties of laser-based optical sensors to provide a repeatable, verifiable, and accurate measure of the presence of TOR friction modifiers on the rail. The measurement system is assembled in a self-contained, portable rail cart that can be pushed on the rail at walking speeds.
Various TOR states are assimilated in the lab for assessing the effectiveness of the laser system. Additionally, the laboratory results are repeated in the field on various tracks, including revenue service track. The results of the tests indicate that the developed system is able to accurately measure the presence of TOR friction modifiers from none to fully-saturated, but is not affected by environmental factors such as rain, sunlight, type of rail, and top-of-rail condition. The measurements provide the means for classifying the state of rail friction in an indexed manner. The results of the study will not only have a significant effect on more efficient use of TOR friction modifiers for promoting better fuel efficiency, but they can also have a major impact on braking practices in applications such as Positive Train Control (PTC).Ph. D.
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Elfick, Alistair Philip David. "A tribological assessment of the porous coated anatomic total hip replacement." Thesis, Durham University, 1999. http://etheses.dur.ac.uk/4574/.
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The tribological performance of internal joint prostheses is a fundamental influence on their longevity. The aim of this study is to characterise the tribological performance of the Porous Coated Anatomic total hip replacement by the analysis of 119 explanted prostheses. Investigations of the friction, wear, surface topography and wear debris were made and related to the joint's clinical performance. The friction of the joints at explant was similar to that of new prostheses. The median total wear volume (419mm(^3)) was found to agree with previous wear studies suggesting the existence of a threshold wear volume which promotes osteolysis. Clinical wear factor for the whole cohort matched that of alternative joint designs. The femoral head finish was shown to degrade but not in proportion to implant duration. The roughness of the UHMWPE liner was shown to fall but no relationship with any head roughness, or temporal, parameter could be distinguished. Simulator studies confirmed that the wear factor of a joint is likely to change over its lifespan. Wear models published previously describing the influence of femoral head roughness on wear could not predict the performance of explanted prostheses. An alternative relationship was observed indicating that head roughness is not as powerful a predictor of wear as previously held. A novel technique for the characterisation of the size distribution of ex vivo and in vitro wear debris was developed. A Low-Angle Laser Light Scattering Particle Analyser was used to size particles continuously over a range from 0.5 to 1000μm. This technique offers considerable unprovement over existing microscope-based methods in terms of the detail of the information and does so with less experimental effort. It was shown to be highly accurate and repeatable in preliminary investigations. Case studies of five tissue samples revealed the potential of this method.
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Rhen, Mats. "Studies of condition monitoring methods for system health assessment : health diagnostics and prognostics." Licentiate thesis, Luleå tekniska universitet, 2002. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-26751.
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Increasing interest in productivity, safety and environmental issues have highlighted the area of maintenance and reliability. The increasing cost of maintenance covers both preservation and sustainable exploitation of resources and awareness in maintaining equipment in a way to ensure return on investment both in the short and long run. The information obtained from condition monitoring of existing turbine, plant, rails and pumps can provide an important basis for dimensioning of future systems and components. The main objective of this research work is to develop and apply methods for efficient condition monitoring, and hence reduce maintenance costs and provide a framework for development and implementation of computer based decision tools. Furthermore, methods enabling existing process data and cost effective transducers to be used together with modern data analysis and diagnostic tools for condition monitoring of complex mechanical systems have been examined and prototypes developed. The areas of investigation covered in this work are hydropower turbines, rails and the main cooling pumps in a nuclear power-plant. The interest in diagnostics for hydropower turbines was driven by the obvious risk of contamination of water by oil leaks and expensive refurbishments caused by wear of the Kaplan turbine vane bearings. The intrest in risk analysis was motivated by Vattenfall's intrest in gaining knowledge about the state of all turbines in the company. The aim of this project was to develop a generic model of hydropower turbine behavior using physics-based models based on material properties, load tolerances, etc.. An important question was whether it was possible to predict the wear rate and plan predictive replacement or maintenance. A systematic approach to find failure modes, their effects, their causes and consequences in combination with Fault Tree Analysis was needed. The objective of this project was to examine a systematic approach to map failure modes and their causes in an hydropower turbine. We have restricted the study to turbine units of the Kaplan, Francis and tube types. The objective of the study concerning rail track was to develop methods and equipment for detection of surface damage in rail track rail in addition to the present system of practice of visual examination. The equipment developed has to be used to obtain objective statistical data for evaluating maintenance methods and efforts. We have restricted the study to spalling and headchecks on the rail head surface and running edge. The method developed enables measurements of different types of surface damage such as spalling and shelling to be made with inductive transducers sensitive to the distance to the measured object. The assumption here is that the damage being detected is characterized by the absence of material from rail surface. The main object of condition monitoring of the cooling pumps was to be able to detect bearing wear in order to be able to plan and carry out restoration well ahead of breakdown or bearing seizure. The study was restricted to the main cooling pump motor and its main bearings. Condition monitoring of the pumps was done using a method based on current measurements. Analysis of the currents on the main cooling pump of the power plant proved that it is possible to monitor the condition of the pump in spite of the presence of electronic frequency converters which distorts the signal.Godkänd; 2002; 20070222 (ysko)
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Söderberg, Anders. "Interface modeling - friction and wear." Doctoral thesis, KTH, Maskinkonstruktion (Avd.), 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9861.
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The general trend toward increased use of computer models and simulations during product development calls for accurate and reliable product models. The function of many products relies on contact interfaces between interacting components. Simulating the behavior of such products requires accurate models of both components and interfaces. Depending on the purpose of the simulation, interface models of different degrees of detail are needed. In simulating very large systems with many interfaces, it might be computationally expensive to integrate detailed models of each individual interface. Condensed models, or abstractions, that describe the interface properties with the fewest degrees of freedom are therefore required. This thesis deals with the modeling and simulation of mechanical interfaces in a systems context. The five appended papers discuss the issue from both the simulation and tribological points of view. The aim is to study how friction and wear can be modeled in the behavioral simulation of technical systems and to discuss the convenience and applicability of using different types of models as building blocks of a system model in simulations. Paper A reviews existing friction models of sliding contacts under different running conditions. Paper B uses a simplified contact model, the elastic foundation model, to model friction in a boundary-lubricated rolling and sliding contact. The model is integrated into a dynamic rigid body model of a mechanical system, and the system behavior is simulated. Paper C discusses the application of the elastic foundation model to rough surface contact problems and investigates how the error in its results depends on surface roughness. Papers D and E address how the wear of the contact surfaces at the pad-to-rotor interface in a passenger car disc brake can be simulated using finite element analysis (FEA).QC 20100811
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Söderberg, Anders. "Interface modeling : friction and wear /." Stockholm : Maskinkonstruktion, Kungliga Tekniska högskolan, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-9861.
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Ogano, Satoshi. "Electrochemical control of friction and wear." Thesis, Imperial College London, 1998. http://hdl.handle.net/10044/1/7416.
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Russell, Serena Louisa. "Friction, wear, wear debris and functional biocompatibility of cartilage substitution biomaterials." Thesis, University of Leeds, 2010. http://etheses.whiterose.ac.uk/12742/.
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The friction, wear and biological response to hydrogels, thermoset and thermoplastic polyurethanes were investigated in order to determine their suitability as potential cartilage substitution biomaterials. A single station pin-on-plate friction rig was utilised to determine the friction properties of these materials when articulated against articular cartilage plates and stainless steel plates. These materials were also reciprocated against stainless steel plates with smooth and rough surfaces using a six station multidirectional wear rig to generate clinically relevant sized wear particles which were characterised in terms of particle number and area as a function of size. Aseptically generated wear particles from the thermoset and thermoplastic polyurethanes were generated utilising a single station pin-on-plate wear rig and cultured with peripheral blood mononuclear cells to establish their biological activity by assessing the release of four cytokines (tumour necrosis factor-alpha, interleukin-lβ, interleukin-6 and interleukin-8) using an enzyme-linked immunosorbent assay. Friction tests demonstrated that articular cartilage (articulated against itself) exhibited a low coefficient of friction which was concurrent with the literature. The thermoplastic polyurethanes and hydrogels (against articular cartilage) exhibited statistically similar friction characteristics compared to articular cartilage against itself, however, the hydrogels generated considerable wear. In contrast, the friction characteristics of the thermoset polyurethanes were significandy higher than the friction of articular cartilage against itself. When wear particles were generated against stainless steel plates with smooth and rough surfaces, it was clear that the largest percentage number of particles were either < 0.1 or 0.1-1.0 11m in size, however, the percentage area of these particles was more variable and was either in the 0.1-1.0 μm, 1-10 μm or > 10 μm size range. Diprane SOD was the least biologically active material, as cells from two donors out of three were stimulated to release elevated levels of cytokines. Diprane SOD and Corethane 5SD were the only two materials to stimulate cells from donors to significandy release three cytokines out of four. All other materials stimulated an elevated level of all four cytokines from cells from all three donors.
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Kong, Hosung. "Friction and wear at sliding ceramic surfaces." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.386230.
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Dong, Sheng. "Friction and Wear Reduction via Ultrasonic Lubrication." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1437560338.
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Schroeder, Matthew O. "Biotribology : articular cartilage friction, wear, and lubrication /." Thesis, This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-12302008-063639/.
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Wänstrand, Olle. "Wear resistant low friction coatings for machine elements." Doctoral thesis, Uppsala University, Department of Materials Science, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-1084.
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By the introduction of machine elements made of light metals, e.g. Al or Mg alloys, which are coated with a material providing high wear resistance and low friction coefficient, both economical and environmental benefits can be gained. A high resistance against wear results in increased lifetime and lower costs for spare parts and maintenance. This also means fewer production stops and less machine downtime. Moreover, a vehicle of lower weight and with reduced friction losses will consume less fuel.
The light metal alloys display low hardness and elastic modulus and in addition they have a high tendency to stick to the countersurface in sliding contact. Hence, to be used in tribologically demanding applications, they must be coated with a material providing low friction and wear. Due to the thin and brittle nature of the available coatings an intermediate load-carrying layer has to be introduced to protect the base material from large deformations and the brittle surface coating from cracking.
In this thesis both experiments and theoretical simulations has shown that the load-carrying layer between the soft and compliant base material and the thin brittle coating should have high elastic modulus and hardness as well as a for the contact situation sufficient thickness.
A number of vapour deposited coatings have been investigated regarding their tribological behaviour with special emphasis on the mechanisms providing low friction. When sliding against steel, it was found that carbon-rich coatings show much lower friction and wear of the countersurface than nitrogen-rich coatings. The explanation is that steel has a tendency to stick to nitrogen-rich coatings, leading to steel against steel contact, but not to carbon-rich coatings. Another explanation is that material is transferred from a carbon-rich coating to the steel and this gives an easily sheared contact with low friction coefficient.
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Mozgovoy, Sergej. "High Temperature Friction and Wear in Press Hardening." Licentiate thesis, Luleå tekniska universitet, Maskinelement, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-26232.
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In the automotive industry, press hardening is usually employed to produce safety orstructural components from advanced high–strength steels. This hot forming process, andthermomechanical forming processes in general, is highly dependent on friction betweentool and workpiece as friction affects and controls the deformation of the workpiece.However, friction is also directly associated with wear of the forming tools. Tool wear isa complex system response depending on contact conditions and is a serious issue whenit comes to process economy as it reduces the service life of the tool. Therefore, it isnecessary to enhance the durability of thermomechanical forming tools by studying theinfluence of parameters such as contact pressure, cyclic thermal loading, repetitive mech-anical loading and others on tool wear. Then, computational mechanics can be utilised tonumerically simulate and optimise the thermomechanical forming process by predictingwear of the tools.Dry sliding tests were carried out on a high temperature reciprocating friction andwear tester. The aim was to identify the occurring wear mechanisms and determine thetribological behaviour of prehardened hot work tool steel when sliding against 22MnB5boron steel. A normal load of 31 N, which corresponds to a contact pressure of 10 MPa, asliding speed of 0.2 ms −1 and temperatures ranging from 40◦Cto800◦ C were employed.It was found that the coefficient of friction and the specific wear rate decreased at elevatedtemperature because of the formation of compacted wear debris layers on the interactingsurfaces.Increasing material and energy expenses, rising demands for process flexibility andstability as well as requirements for minimal trial and error have led to a growing interestin numerical simulation of wear phenomena. Finite element simulations of a strip drawingtest were conducted to explore the possibility of predicting tool wear in press hardening.The focus laid on unveiling the contact conditions on the forming tools through numericalsimulation. The influence of high temperature on wear was studied and the results wereimplemented in Archard’s wear model to introduce temperature dependence. Further-more, another wear model used for warm forging was also considered. It was found thatthe extreme contact conditions occurred at tool radii and that the different wear modelsled to similar wear depth profiles on the radii but with different orders of magnitude.Standard high temperature tribometers allow fundamental tribological studies to becarried out in order to investigate the tribological behaviour of the materials in contact.However, the conditions prevalent during the interaction of the hot workpiece and toolsurfaces in thermomechanical forming are not adequately simulated in these tribometers.A novel high temperature tribometer has been employed in order to more closely simulatethe interaction between tool and workpiece at elevated temperatures during thermomech-anical forming. It was found that a higher load led to a lower and more stable coefficientGodkänd; 2014; 20140919 (sermoz); Nedanstående person kommer att hålla licentiatseminarium för avläggande av teknologie licentiatexamen. Namn: Sergej Mozgovoy Ämne: Maskinelement/Machine Elements Uppsats: High Temperature Friction and Wear in Press Hardening Examinator: Professor Braham Prakash, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet Diskutant: Dr Manel Rodriguez Ripoll, AC2T research GmbH, Österrike Tid: Fredag den 21 november 2014 kl 10:00 Plats: E231, Luleå tekniska universitet
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Lindholm, Per. "Wear resistant low friction coatings for engine components." Doctoral thesis, Stockholm, 2004. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-54.
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Thomas, Ben. "Friction and wear performance of lifeboat launch slipways." Thesis, Bournemouth University, 2009. http://eprints.bournemouth.ac.uk/14521/.
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The Royal National Lifeboat Institution provides a marine search and rescue service using lifeboat stations sited along the coast of the UK and Ireland. In locations where there is no natural harbour or where there is a large tidal range it is necessary to use an inclined slipway to launch a large lifeboat. Lifeboat slipway stations consist of an initial section where the boat is held on rollers followed by an inclined keelway of nickel/chromium coated steel, the lifeboat is released from the top of the slipway and proceeds under its own weight into the water. The lifeboat is subsequently recovered to the top of the slipway using a winch line. With the introduction of the new, larger Tamar class lifeboat existing boathouses are being upgraded and existing low friction coated steel slipway lining materials replaced with a low-friction jute fibre/phenolic resin composite. The composite slipway lining material was selected in part because it was able to run unlubricated or water lubricated. However the friction problems have been such that it is usual to line the slipway with grease before every launch and recovery. This adds to the number of operations involved in a launch and has safety implications. The use of grease to line the slipway results in the grease being washed out to sea with effects on the surrounding area, it is likely that there is some environmental impact due to this as the grease is non-biodegradeable and not recommended for open water use according to the material data sheet. Because of these issues it is desirable to develop a set of working guidelines for crews to reduce both these risks by setting appropriate conditions for the manual application of grease along the slipway. These guidelines will also feature a method of assessing the wear of slipway panels so that panels can be replaced before they present a hazard to lifeboat operation. This thesis describes a method for assessing slipway lining materials and lubricants. Appropriate tribometer test machines are selected to assess slipway lining materials performance, the TE57 reciprocating tribometer and the TE92 rotary tribometer are used in conjunction to ascertain friction and wear performance respectively. These results are combined with detailed slipway panel surveys and case studies, and with Finite Element models to develop a method for assessing and predicting the friction and wear along a panel lined slipway. These results are used to develop slipway performance monitoring techniques for lifeboat crews and to develop design modification to combat high friction and wear on slipway panels. The adoption of a modified slipway panel and water lubrication system is proposed, this arrangement reduces panel misalignment contributions to slipway friction and wear resulting in more reliable slipway performance and is also projected to save the RNLI up to £195k annually compared with current practice.
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Daloia, Debora. "Friction and Wear Behavior of Graphene Reinforced Epoxy." University of Dayton / OhioLINK, 2014. http://rave.ohiolink.edu/etdc/view?acc_num=dayton1403532384.
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Howell, Gavin John. "Wear of aluminium MMCs against automobile friction materials." Master's thesis, University of Cape Town, 1994. http://hdl.handle.net/11427/12691.
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Includes bibliographical referencesTwo magnesium/silicon aluminium alloys each reinforced with 20 vol. % SiC particulates have been worn against three different automobile friction linings (brake pads). Two of the friction linings are commonly used against cast iron brake rotors while the third has been formulated for use against aluminium MMC brake rotors. Wear processes at the interfaces of the specific rotor - pad combinations have been characterised through the analysis of friction traces and the use of optical and electron microscopy. Models on the interdependence of friction and wear, and models of wear mechanisms for aluminium MMCs and cast iron sliding against friction materials have been proposed and discussed. For an aluminium MMC sliding against an organic pad formulated for use against cast iron, wear rates are low and friction is constant due to the formation of a solid lubricant layer at the wear interface. When this MMC is worn against a semi-metallic pad formulated for use against cast iron, wear rates are extremely high due to two and three body abrasion which lead to subsurface delamination and early melt wear in the MMC. For an aluminium MMC developed for its use in automobile brake rotors sliding against a semi-metallic pad specifically formulated for its use against MMC brake rotors, wear rates at low loads are low although friction traces are irregular and fracture of the SiC particulates occurs at the lowest load and sliding velocity. This fracture of SiC is caused by the abrasive action of hard alumina particles within the pad. At high loads and sliding velocities cohesiveness of materials within the pad is poor and the wear rate of the MMC is extremely high. At the highest load/sliding velocity combination, the wear resistance of the MMC is inferior to that of its unreinforced matrix. If the structure and composition of friction linings are arranged correctly, the wear resistance and frictional performance of aluminium MMC brake rotors are superior to those of cast iron brake rotors. In addition, the lower density of aluminium MMCs provides for an economic advantage over cast iron with respect to efficient use of fuel, and fabrication expenses.
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Mussa, Abdulbaset. "Wear characterization and wear mapping of a coated cutting tool : Development of cutting tool test fixture and wear testing." Thesis, Karlstads universitet, Science, Mathematics and Engineering Education Research (SMEER), 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-37790.
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Wear mechanisms of the cutting tools are well investigated worldwide. Usually researchers use the cutting process itself, turning by single point cutting, as their investigation method, which includes turning a metal cylinder with a pre-selected work-material and predetermined cutting conditions. Thereafter the tool worn surface is examined by scanning electron microscopy in order to characterize the tool wear mechanisms and tool failure. However, this may be the most appropriate way to investigate the wear mechanisms which occur during machining since it simulates the real operation. Metal cutting involves extreme conditions such as high temperature and high-pressure and the different condition results in different wear modes on the insert’s surface. The wear modes are overlapping and the transition boarder between them are not sharp making it difficult to obtain a detailed information of wear mechanisms. Because of these reasons many researchers try to refine the machining to a single condition e.g; high pressure, at the laboratory level in order to characterize the wear mechanisms and to get a more detailed information. In this thesis the wear tests of the cutting tool are performed by using a slider-on-flat-surface (SOFS) wear tester. SOFS involves a normal load, which applies to the sample and a tangential force that enables the sliding of the sample against a counterface. To enable conducting the wear tests in SOFS a newly design of tool holder was prepared. The wear tests were performed at different contact conditions and the stainless steel EN 1.4310 was used as the counterface material. After the tools were tested, the worn surface of the tool was examined by optical light microscopy and scanning electron microscopy in order to identify the wear rate and wear mechanisms. At low load the dominating wear mechanism was adhesive wear. The adhesive wear was induced by material pick-up during sliding i.e. material from the counterface was transferred to the insert’s surface. Further sliding results in delamination of the insert surface and removal of a part of the coatings material. At high load the dominating wear mechanism was a combination of severe adhesive wear and fracture of the coating material. The fracture of the coating material occurred because of overloading. Coating defects promote crack formation under high load and these cracks propagate through the coating during sliding movement and result in microchipping of the coating material. This procedure does not simulate the metal cutting but it still gives an understanding of the behavior of the coating material when it is exposed to a high mechanical stress.
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SUH, Min-Soo. "Wear Mechanisms on SiC and SiC/SiC Composites under Sliding Friction and Erosive Wear." Kyoto University, 2010. http://hdl.handle.net/2433/126768.
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Farhat, Zoheir N. "Friction and wear of nanocrystalline materials and nanolaminated composites." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1996. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/NQ30282.pdf.
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Gay, Russell. "Friction and wear behaviour of self lubricating bearing liners." Thesis, Cardiff University, 2013. http://orca.cf.ac.uk/51031/.
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The thesis describes a numerical model for evaluating the variation of friction and wear of a self lubricating bearing liner over its useful wear life. Self-lubricating bearings have been in widespread use since the mid-1950s, particularly in the aerospace industry where they have the advantage of being low maintenance components. They are commonly used in relatively low speed, reciprocating applications such as control surface actuators, and usually consist of a spherical bearing with the inner and outer elements separated by a composite textile resinbonded liner. A finite element model has been developed to predict the local stiffness of a particular liner at different states of wear. Results obtained using the model were used to predict the overall friction coefficient as it evolves due to wear, which is a novel approach. Experimental testing was performed on a bespoke flat-on-flat wear test rig with a reciprocating motion to validate the results of the friction model. These tests were carried out on a commercially-available bearing liner, predominantly at a high contact pressure and an average sliding speed of 0.2 ms-1. Good agreement between predicted and experimentally measured wear was obtained when appropriate coefficients of friction were used in the friction model, and when the reciprocating sliding distance was above a critical value. A numerical wear model was also developed to predict the trend of backlash development in real bearing geometries using a novel approach. Results from the wear model were validated against full-scale bearing tests carried out elsewhere by the sponsoring company. Good agreement was obtained between the model predictions and the experimental results for the first 80% of the bearing wear life, and explanations for the discrepancy during the last 20% of the wear life have been proposed.
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Utter, Jason Richard. "Nanoscale adhesion, friction and wear of proteins on polystyrene." The Ohio State University, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=osu1348681051.
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Gåård, Anders. "Wear in sheet metal forming." Licentiate thesis, Karlstad University, Faculty of Technology and Science, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:kau:diva-1592.
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The general trend in the car body manufacturing industry is towards low-series production and reduction of press lubricants and car weight. The limited use of press lubricants, in combination with the introduction of high and ultra-high strength sheet materials, continuously increases the demands of the forming tools. To provide the means of forming new generations of sheet material, development of new tool materials with improved galling resistance is required, which may include tailored microstructures, introducing of specific(MC, M(C,N))carbides and nitrides, coatings and improved surface finish. In the present work, the wear mechanisms in real forming operations have been studied and emulated on a laboratory scale by developing a test equipment. The wear mechanisms identified in the real forming process, were distinguished into a sequence of events consisting of initial local adhesive wear of the sheets resulting in transfer of sheet material to the tool surfaces. Successive forming operations led to growth of the transfer layer and initiation of scratching of the sheets. Finally, scratching changed into severe adhesive wear, associated with gross macroscopic damage. The wear process was repeated in the laboratory test-equipment in sliding between several tool materials, ranging from cast iron to conventional ingot cast tool steels to advanced powder metallurgy tool steel, against dual-phase carbon steel sheets. By use of the test-equipment, selected tool materials were ranked regarding wear resistance in sliding against ferritic-martensitic steel sheets at different contact pressures.
Wear in sheet metal forming is mainly determined by adhesion; initially between the tool and sheet surface interaction and subsequently, after initiation of material transfer, between a sheet to sheet contact. Atomic force microscopy force curves showed that adhesion is sensitive to both chemical composition and temperature. By alloying of iron with 18wt.% Cr and 8wt.% Ni, alloying in itself, or changes in crystal structure, led to an increase of 3 times in adhesion at room temperature. Hence, alloying may be assumed a promising way for control of adhesive properties. Additionally, frictional heating should be controlled to avoid high adhesion as, generally, adhesion was found to increase with increasing temperature for all investigated materials.
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Flitcroft, S. M. "The friction and wear characteristics of a sintered metal motorcycle friction braking material, under wet and dry conditions." Thesis, Brunel University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.278371.
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Hayward, I. P. "The friction and strength properties of diamond." Thesis, University of Cambridge, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.235115.
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Diamonds have many extreme physical properties that lead to a host of technological applications. Their main use as a tool or abrasive for the machining of hard materials involves diamonds rubbing against the material being worked and often against each other. The strength and frictional properties of diamond are thus of great practical, as well as academic interest. Studies of the reciprocating sliding of one diamond on another for extended periods have shown that the changes in friction and wear are linked with the formation of debris. Analysis of the debris shows it does not consist of diamond fragments. Investigations of the effect of low-pressure gases on diamond friction also indicate debris plays an important role, and that the friction and wear are markedly dependent on the state of adsorbants on the diamond surface. Details are also given of the friction and wear of steel, glass and sintered diamond in contact with diamond. An associated study of the solid particle erosion of diamond has shown that cracking can occur at impact velocities of 25 m s-1. To facilitate the friction studies two existing friction apparatus have been automated. Computer control now allows data to be collected and analysed more rapidly and thoroughly than was possible before. The equipment has also been adapted to extend the conditions under which friction studies can be made.
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Ujvari, Szerena Krisztina. "Journal Bearing Friction Optimization." Thesis, Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-60669.
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Engine downsizing, improving fuel efficiency while satisfying the environmental legislations are one of the main driving forces in developing new solutions for passenger cars.Engine main bearings, are journal bearings which support the crankshaft and operate principally in full film lubrication. Defining the optimum design parameters of the bearings which can provide low friction and high durability for automobiles represents a multi-variable problem.Being the supporters of the main shaft driven by the internal combustion engine, main bearings are subjected to strenuous operating conditions. These include high loads and pressures amongst others. The trend in lubricant selection for these components is shifting towards choosing engine oils with lower viscosity to further reduce fuel consumption. Simultaneously with the shift in oil, new solutions for controlling the geometry and the topography on the micro-scale are becoming available. Three main bearing top layers plated on a conventional aluminum alloy containing tin and silicon were selected for the study. The top layers, one bismuth based and two newly developed polymer based, were investigated for their frictional and wear performance.In order to study experimentally the influence of different design parameters on bearing performance a test rig and a methodology was developed. The selected engine main bearings were tested in lubricated condition with two oils having different viscosity. Pre - and post test analysis of the shaft surface roughness was performed using white light interferometry. The wear performance of the bearings was measured both as mass loss and surface topography.The results suggest that the developed test rig can be used to simulate close to running condition testing. The measurement method and set up shows good consistency at a load of 2000 N, but indicates inconsistency in set up at 500 N.It is found that the newly developed engine main bearing top layers have promising frictional and wear performance, providing a reduction in friction by up to 20%.
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Carvalho, Bittencourt André. "Modeling and Diagnosis of Friction and Wear in Industrial Robots." Doctoral thesis, Linköpings universitet, Reglerteknik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-109335.
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High availability and low operational costs are critical for industrial systems. While industrial equipments are designed to endure several years of uninterrupted operation, their behavior and performance will eventually deteriorate over time. To support service and operation decisions, it is important to devise methods to infer the condition of equipments from available data. The monitoring of industrial robots is an important problem considered in this thesis. The main focus is on the design of methods for the detection of excessive degradations due to wear in a robot joint. Since wear is related to friction, an important idea for the proposed solutions is to analyze the behavior of friction in the joint to infer about wear. Based on a proposed friction model and friction data collected from dedicated experiments, a method is suggested to estimate wear-related effects to friction. As it is shown, the achieved estimates allow for a clear distinction of the wear effects even in the presence of large variations to friction associated to other variables, such as temperature and load. In automated manufacturing, a continuous and repeatable operation of equipments is important to achieve production requirements. Such repetitive behavior of equipments is explored to define a data-driven approach to diagnosis. Considering data collected from a repetitive operation, an abnormality is inferred by comparing nominal against monitored data in the distribution domain. The approach is demonstrated with successful applications for the diagnosis of wear in industrial robots and gear faults in a rotating machine. Because only limited knowledge can be embedded in a fault detection method, it is important to evaluate solutions in scenarios of practical relevance. A simulation based framework is proposed that allows for determination of which variables affect a fault detection method the most and how these variables delimit the effectiveness of the solution. Based on an average performance criterion, an approach is also suggested for a direct comparison of different methods. The ideas are illustrated for the robotics application, revealing properties of the problem and of different fault detection solutions. An important task in fault diagnosis is a correct determination of presence of a condition change. An early and reliable detection of an abnormality is important to support service, giving enough time to perform maintenance and avoid downtime. Data-driven methods are proposed for anomaly detection that only require availability of nominal data and minimal/meaningful specification parameters from the user. Estimates of the detection uncertainties are also possible, supporting higher level service decisions. The approach is illustrated with simulations and real data examples including the robotics application.För industriella system är både hög tillgänglighet och låga driftskostnader avgörande. Industriella system är oftast utformad för att klara flera års oavbruten drift, men över tid kommer beteendet och prestandan så småningom att förändras. Det är därför viktigt att ta fram metoder som kan extrahera information från tillgänglig data och dra slutsatser om systemets beteende, som i sin tur används som stöd för beslut angående systemets fortsatta drift.Denna avhandling handlar om utformning och utvärdering av diagnostiska metoder för att stödja tids- och kostnadseffektiva beslut angående den fortsatta driften för systemet. I synnerhet studeras problemet med att upptäcka för höga nivåer av slitage i respektive led för en industrirobot. Eftersom slitage påverkar friktionen kan det vara en bra id{\'e} att analysera friktionen för att uppskatta hur stort slitage som har uppkommit. Baserat på en föreslagen friktionsmodell och friktionsdata från specialanpassade experiment föreslås en metod för att uppskatta slitagets omfattning. Metoden försöker anpassa modellen så att sannolikheten att mätningarna kommer från den föreslagna modellen maximeras. Det visar sig att tillförlitliga beräkningar av slitaget kan uppnås även vid stora variationer i belastningen på roboten samt temperaturen i robotens leder, vilket gör det möjligt att planera underhåll för roboten innan den går sönder. Vidare undersöks hur ett systems repetitiva beteende, som är vanligt inom automatiserad tillverkning, kan utnyttjas för att skapa en metod för diagnos som endast använder befintlig data utan hjälp av någon modell. Med hjälp av data som har samlats in från en repetitiv process kan en förändring av processen upptäckas genom att jämföra data från systemet i felfri drift och befintlig drift. Metoden som föreslås utnyttjar den empiriska sannolikhetsfördelningen för systemet i felfri respektive befintlig drift. Det visar sig att metoden med framgång kan detektera slitage i lederna för en industrirobot samt växelfel i en roterande mekanism.I avhandlingen föreslås också metoder för feldetektering. Testet går ut på att man jämför två hypoteser mot varandra genom ett statistiskt ramverk. För att upptäcka en förändring av ett system är det naturligt att de två hypoteserna motsvarar ett system utan fel respektive ett system med fel. Det enda som förutsätts är att data från systemet utan fel är tillgängligt. En annan viktig del är att kunna jämföra olika diagnosmetoder för att se vilken som passar bäst till det aktuella problemet. Ett ramverk baserat på simuleringar har därför föreslagits för utvärdering av diagnosmetoder. Ramverket kan användas för att avgöra vilka variabler som påverkar metoden mest, hur man jämför olika metoder samt hur man bestämmer det effektiva användningsområdet för respektive metod. De föreslagna diagnosmetoderna och ramverket för utvärdering av diagnosmetoderna är generella men illustreras i avhandlingen på tillämpningar för industrirobotar.
Vinnova Excellence Center LINK-SIC
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Mazilu, Dan A. "Wear and friction studies of alumina: Correlation with electron triboemission." Diss., Virginia Tech, 2002. http://hdl.handle.net/10919/30140.
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The first question addressed in this thesis is whether the cumulative triboemission from the abrasion of alumina by a diamond indenter (repeat-pass sliding) correlates with the volume of material removed and, in particular, whether transitions in the rate of material removal are mirrored in the cumulative triboemission rate. As a function of load and number of diamond passes, several wear regimes are observed that are characterized from SEM micrographs by different relative proportions of plastic flow material and fractured surface in the wear scar. In all but one wear regime, the correlation between the wear volume and cumulative triboemission is modest (linear regression coefficient R2 = 0.71); including the one atypical wear regime worsens the correlation. The wear volume and cumulative triboemission are shown to be random variables with normal and lognormal distributions, respectively. Again, excluding the atypical wear regime, the correlation between the logarithms of the estimated population means is significantly better (R2 = 0.91) than the correlation between wear volume and cumulative triboemission for individual samples. In addition to the overall correlation between wear volume and cumulative triboemission, transitions from one wear regime to another are marked by changes in the slope of the mean cumulative triboemission versus pass number. These transitions correlate with the relative fraction of plastic flow debris in the wear scar.
The second question addressed in this thesis is whether the introduction of the chemical vapor aluminum tri-sec butoxide, [C2H5CH(CH3)O]3Al, ATSB, into the boundary layer of an alumina-on-alumina sliding contact can reduce wear and friction. A split-plot factorial experiment was conducted; the factors tested, in addition to the presence or absence of ATSB, were normal load, sliding speed, and surface roughness. The main conclusions of the experiment are that ATSB has no statistically significant effect on specific wear, but that the presence of ATSB reduces friction by 21% at low sliding speed (0.02 m/s) and increases friction by 26% at high sliding speed (1.2 m/s).Ph. D.
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Nadimpalli, Chandrasekhar Venkata. "Friction and wear behavior of silicon under conditions of sliding /." The Ohio State University, 1992. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487779120907373.
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Cooper, David. "The boundary lubricated friction and wear of low alloy steel." Thesis, Aston University, 1989. http://publications.aston.ac.uk/8067/.
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Pin on disc wear machines were used to study the boundary lubricated friction and wear of AISI 52100 steel sliding partners. Boundary conditions were obtained by using speed and load combinations which resulted in friction coefficients in excess of 0.1. Lubrication was achieved using zero, 15 and 1000 ppm concentrations of an organic dimeric acid additive in a hydrocarbon base stock. Experiments were performed for sliding speeds of 0.2, 0.35 and 0.5 m/s for a range of loads up to 220 N. Wear rate, frictional force and pin temperature were continually monitored throughout tests and where possible complementary methods of measurement were used to improve accuracy. A number of analytical techniques were used to examine wear surfaces, debris and lubricants, namely: Scanning Electron Microscopy (SEM), Auger Electron Spectroscopy (AES), Powder X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), optical microscopy, Back scattered Electron Detection (BSED) and several metallographic techniques. Friction forces and wear rates were found to vary linearly with load for any given combination of speed and additive concentration. The additive itself was found to act as a surface oxidation inhibitor and as a lubricity enhancer, particularly in the case of the higher (1000 ppm) concentration. Wear was found to be due to a mild oxidational mechanism at low additive concentrations and a more severe metallic mechanism at higher concentrations with evidence of metallic delamination in the latter case. Scuffing loads were found to increase with increasing additive concentration and decrease with increasing speed as would be predicted by classical models of additive behaviour as an organo-metallic soap film. Heat flow considerations tended to suggest that surface temperature was not the overriding controlling factor in oxidational wear and a model is proposed which suggests oxygen concentration in the lubricant is the controlling factor in oxide growth and wear.
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Boone, Jacob Dee. "Design, Construction and Evaluation of Universal Friction Tester." OpenSIUC, 2010. https://opensiuc.lib.siu.edu/theses/307.
Full textAbstract:
AN ABSTRACT OF THE THESIS OF Jacob Boone, for the Master of Science degree in Mechanical Engineering, presented on 10/28/2010, at Southern Illinois University Carbondale. TITLE: DESIGN, CONSTRUCTION, AND EVALUTAION OF UNIVERSAL FRICTION TESTER MAJOR PROFESSOR: Dr. Peter Filip Many different types of friction testers are currently available for testing specific frictional applications. Of these machines very few have versatility, and of the ones that do, the amount of versatility is limited. Since friction is a property specific to each system, all operating parameters need to match the specific application as closely as possible in order to obtain accurate data. This requires many research facilities to have several specific friction testers in order to provide the necessary testing capabilities. The goal of this project was to design a Universal Friction Tester (UFT) with enough versatility to reproduce most types of sliding friction situations. This was accomplished by providing a wide range of testing capabilities through the use of interchangeable system components. Results show that the UFT provides quality data over its entire operating range. It was shown that normal pressure, sliding speed, temperature and system stiffness all have drastic effects on frictional performance. By using a borosilicate glass disc, the friction surface was viewed in-situ during testing. This allowed insights into true surface temperature and contact area. In conclusion, the UFT can successfully take the place of several friction testers and thus provide many friction research capabilities while requiring fewer resources. The wide range of testing capabilities will allow the UFT to be used as a research tool for many types of advanced friction studies. Some of these may include true surface temperatures, true contact area, influence of conditions on stick-slip phenomenon, and thermo-elastic instabilities.
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Ghasripoor, Farshad. "Friction and wear of a short fibre reinforced aluminium-silicon alloy." Thesis, Brunel University, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.278286.
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Hutton, Toby. "The friction and wear of carbon-carbon composites for aircraft brakes." Thesis, University of Bath, 1996. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.760692.
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Maharaj, Dave. "Friction, Wear and Mechanical Behavior of Nano-Objects on the Nanoscale." The Ohio State University, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=osu1418239204.
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Proprentner, Daniela. "Friction, wear and tangential stiffness of metal surfaces under fretting conditions." Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/9992.
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Bladed disk vibrations in turbomachinery can lead to failure due to High Cycle Fatigue. One way in which vibration may be reduced is by dry friction damping. Frictional damping originates from micro and macro slip in the contacting interfaces (“joints”) and is controlled by the relationship of the applied load and tangential displacement. In order to predict the dynamic response of the structure, knowledge of the coefficient of friction and the tangential contact stiffness of the contact are crucial. Vibration induced slip and the consequent damage in contacting surfaces has been widely studied and is usually called fretting. However, little is known about the effect of the changing interface during fretting on the coefficient of friction and the tangential contact stiffness, which is required when trying to predict these parameters. This study seeks an improved understanding of the effects of surface topography, surface chemistry, and elastic and plastic material properties on the friction and damping performance of joints under fretting conditions. In the present study experiments were conducted to measure the coefficient of friction and the tangential contact stiffness of different metals under different test conditions. Fretting damage mechanisms were investigated using metallography, SEM, EBSD, TEM and XRD techniques. The evolution of roughness and conformity was investigated by using interferometric profiling systems and image registration via cross correlation. An infrared radiation measuring system was employed to measure the dissipated radiation and frictional power in fretting which was then compared with calculated energy dissipation maps. Experimental results were used to validate models predicting contact stiffness which have been developed throughout the project by collaborating researchers. This study highlighted real contact conditions and their dependence on running time, which need to be taken into account when modelling friction contacts.
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Freeman, Mark E. "Friction, wear and lubrication of a poly(2-hydroxyethyl methacrylate) hydrogel." Thesis, This resource online, 1996. http://scholar.lib.vt.edu/theses/available/etd-09182008-063516/.
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Hofmann, Dieter. "Si-DLC coatings optimized for low wear and low friction applications." Thesis, Sheffield Hallam University, 2014. http://shura.shu.ac.uk/19805/.
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Diamond-like carbon (DLC) has excellent properties for the use as tribological coating such as high hardness, high wear resistance and a low friction coefficient. Nanolayer systems of hydrogenated diamond-like carbon (a-C:H) and silicon doped hydrogenated diamond-like carbon (Si-DLC or a-C:H:Si) have been studied. The objectives of this work are to develop layer combinations which allow combining low abrasive wear, low friction properties, and improved temperature stability for the coatings. A literature survey on sputtering, plasma enhanced chemical vapor deposition (PECVD) and carbon based materials with a focus on a-C:H and Si-DLC coatings is given. This survey includes a brief overview of the 60 years history of DLC coating. In the second part of the thesis, the experimental set up for the layer preparation by a magnetron based deposition method and a basic description of the process are presented. Using sputtering from a solid SiC target as a source of the Si for the Si-DLC instead of the commonly used PECVD process with Si-containing precursors Si-DLC/a-C:H nanolayers were deposited at high deposition rates. For the coatings, the influence of the acetylene gas flow, the bias voltage, and the hydrogen and silicon concentration are discussed. Undoped a-C:H coatings with high indentation hardness above 40 GPa and very low abrasive wear rates of 0.6 x 10[-15] m[3]/(Nm) and low hydrogen content of about 11 at.% were deposited. Si-DLC/a-C:H nanolayer coatings with high hardness of 20 to 30 GPa and a high temperature stability up to 500 °C were prepared. For these nanolayer films low friction coefficients of 0.06 to 0.11 and high abrasive wear rates of > 2.5 x 10[-15] m3/(Nm) were achieved at high silicon contents above 15 at.%. On the other hand nanolayer coatings with low silicon contents of less than 10 at.% showed low wear rates below 1.7 x 10[-15] m3/(Nm) combined with higher friction coefficients of 0.12 to 0.15. In order to combine the low abrasive wear rate and the low friction coefficient at first a Si-DLC/a-C:H layer with low Si-concentration followed by a second layer with high Si-concentration was deposited. Due to the low surface free energy of Si-DLC coatings of 30 to 35 mN/m the wetting behavior for some lubricants may deteriorate. In this case a further optimization of the nanolayer system is required.
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Carvalho, Bittencourt André. "On Modeling and Diagnosis of Friction and Wear in Industrial Robots." Licentiate thesis, Linköpings universitet, Reglerteknik, 2012. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-72975.
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Industrial robots are designed to endure several years of uninterrupted operation and therefore are very reliable. However, no amount of design effort can prevent deterioration over time, and equipments will eventually fail. Its impacts can, nevertheless, be considerably reduced if good maintenance/service practices are performed. The current practice for service of industrial robots is based on preventive and corrective policies, with little consideration about the actual condition of the system. In the current scenario, the serviceability of industrial robots can be greatly improved with the use of condition monitoring/diagnosis methods, allowing for condition-based maintenance (cbm). This thesis addresses the design of condition monitoring methods for industrial robots. The main focus is on the monitoring and diagnosis of excessive degradations caused by wear of the mechanical parts. The wear processes may take several years to be of significance, but can evolve rapidly once they start to appear. An early detection of excessive wear levels can therefore allow for cbm, increasing maintainability and availability. Since wear is related to friction, the basic idea pursued is to analyze the friction behavior to infer about wear. To allow this, an extensive study of friction in robot joints is considered in this work. The effects of joint temperature, load and wear changes to static friction in robot a joint are modeled based on empirical observations. It is found that the effects of load and temperature to friction are comparable to those caused by wear. Joint temperature and load are typically not measured, but will always be present in applications. Therefore, diagnosis solutions must be able to cope with them. Different methods are proposed which allow for robust wear monitoring. First, a wear estimator is suggested. Wear estimates are made possible with the use of a test-cycle and a friction model. Second, a method is defined which considers the repetitive behavior found in many applications of industrial robots. The result of the execution of the same task in different instances of time are compared to provide an estimate of how the system changed over the period. Methods are suggested that consider changes in the distribution of data logged from the robot. It is shown through simulations and experiments that robust wear monitoring is made possible with the proposed methods.
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TAMATAM, LAKSHMINARAYANA REDDY. "Effect of wear on the dynamics of structures with friction contacts." Doctoral thesis, Politecnico di Torino, 2021. http://hdl.handle.net/11583/2929758.
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Bhattacharya, Victoria. "Study Of Friction And Wear Behaviour Of Nano-Embedded Aluminium Alloys." Thesis, Indian Institute of Science, 2000. https://etd.iisc.ac.in/handle/2005/190.
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In general, the bearing alloys have two types of microstructure i.e., either a soft matrix with discrete hard particles or a continuous matrix of the harder metal with small amount of the softer metal finely dispersed in it. The aluminium and copper based bearing alloys which are widely studied fall in the second category. However, the bearing materials which have been studied have micron sized dispersoids. In recent times, it is possible to produce nanoscale dispersoids in a hard matrix by the novel processing route of rapid solidification. This offers an opportunity to study the small length scale effect on tribological processes. In this thesis, we deal with aluminium alloys where nanoscaled dispersions of lead, bismuth and indium are produced by rapid solidification processing. Chapter 1 of the thesis is an introduction, followed by Chapter 2, which reviews the literature on nanomaterials. Special attention is given to the monotectic system, followed by a brief description on friction and wear of materials which is necessary for our present investigation. The details of experimental and characterisation techniques are given in Chapter 3. In Chapter 4, we present a brief study of white metal bearings (babbit). Tin-based babbit of composition, Sn-6wt% Cu-llwt% Sb was studied. The study of babbit was mainly carried out with the idea that it could serve as a benchmark for subsequent studies in aluminium alloys, in terms of tribological properties. In particular, we have carried out a detailed electron microscopic investigation on the phases present in the bearing alloy. The friction and wear behaviour of this material confirms the proper calibration of our setup for wear studies. This is followed by a detailed study on the synthesis, microstructure and tribological behaviour of nanodispersed aluminium alloys, Al-6wt% Pb and Al-10wt% Pb in Chapter 5.
For comparison, we have also studied melt-spun aluminium without dispersoids. Detailed electron microscopic characterisation indicates that lead has a cube on cube orientation relationship with the aluminium matrix, and the particles exhibit a lognormal distribution with the mode of the particle size distribution being 15 nm. The pin on disc results suggest a distinct lowering of coefficient of friction corresponding to pure aluminium (μ= 0.40) and as cast aluminium-lead alloys (μ= 0.41). Detailed SEM studies indicate a tribolayer consisting primarily of Al, Pb and Fe. The later comes from the counterface material. Our results clearly indicate that at an early stage, little or no oxidation takes place at the sliding interface. TEM observations indicate significant deformation of lead particles in the sub-surface region. The observations suggest spreading of the lead, which acts as a lubricating layer. Wear behaviour is primarily adhesive and follows Archard's wear law. However, the rate of wear is less than that reported by other investigators on micronsized lead dispersions in aluminium. In Chapter 6, we present the results for alloys dispersed with nanosized indium and bismuth. We show that indium particles on melt-spinning exhibit both cubic and tetragonal crystal structure. The indium particles are coarser (with a mode of 25 nm) than the lead and bismuth particles (which have mode of 15nm). The bismuth containing alloys have a lower wear rate and coefficient of friction compared to lead and indium alloys. However, both indium and bismuth particles do not follow Archard's wear law and the wear vs load graph shows a non-linear behaviour. The results are discussed in terms of known mechanisms of the coefficient of friction and wear. Chapter 7 gives the salient conclusions while in Chapter 8 we discuss some of the unanswered questions and the potential for future work in this field.
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Bhattacharya, Victoria. "Study Of Friction And Wear Behaviour Of Nano-Embedded Aluminium Alloys." Thesis, Indian Institute of Science, 2000. http://hdl.handle.net/2005/190.
Full textAbstract:
In general, the bearing alloys have two types of microstructure i.e., either a soft matrix with discrete hard particles or a continuous matrix of the harder metal with small amount of the softer metal finely dispersed in it. The aluminium and copper based bearing alloys which are widely studied fall in the second category. However, the bearing materials which have been studied have micron sized dispersoids. In recent times, it is possible to produce nanoscale dispersoids in a hard matrix by the novel processing route of rapid solidification. This offers an opportunity to study the small length scale effect on tribological processes. In this thesis, we deal with aluminium alloys where nanoscaled dispersions of lead, bismuth and indium are produced by rapid solidification processing. Chapter 1 of the thesis is an introduction, followed by Chapter 2, which reviews the literature on nanomaterials. Special attention is given to the monotectic system, followed by a brief description on friction and wear of materials which is necessary for our present investigation. The details of experimental and characterisation techniques are given in Chapter 3. In Chapter 4, we present a brief study of white metal bearings (babbit). Tin-based babbit of composition, Sn-6wt% Cu-llwt% Sb was studied. The study of babbit was mainly carried out with the idea that it could serve as a benchmark for subsequent studies in aluminium alloys, in terms of tribological properties. In particular, we have carried out a detailed electron microscopic investigation on the phases present in the bearing alloy. The friction and wear behaviour of this material confirms the proper calibration of our setup for wear studies. This is followed by a detailed study on the synthesis, microstructure and tribological behaviour of nanodispersed aluminium alloys, Al-6wt% Pb and Al-10wt% Pb in Chapter 5.
For comparison, we have also studied melt-spun aluminium without dispersoids. Detailed electron microscopic characterisation indicates that lead has a cube on cube orientation relationship with the aluminium matrix, and the particles exhibit a lognormal distribution with the mode of the particle size distribution being 15 nm. The pin on disc results suggest a distinct lowering of coefficient of friction corresponding to pure aluminium (μ= 0.40) and as cast aluminium-lead alloys (μ= 0.41). Detailed SEM studies indicate a tribolayer consisting primarily of Al, Pb and Fe. The later comes from the counterface material. Our results clearly indicate that at an early stage, little or no oxidation takes place at the sliding interface. TEM observations indicate significant deformation of lead particles in the sub-surface region. The observations suggest spreading of the lead, which acts as a lubricating layer. Wear behaviour is primarily adhesive and follows Archard's wear law. However, the rate of wear is less than that reported by other investigators on micronsized lead dispersions in aluminium. In Chapter 6, we present the results for alloys dispersed with nanosized indium and bismuth. We show that indium particles on melt-spinning exhibit both cubic and tetragonal crystal structure. The indium particles are coarser (with a mode of 25 nm) than the lead and bismuth particles (which have mode of 15nm). The bismuth containing alloys have a lower wear rate and coefficient of friction compared to lead and indium alloys. However, both indium and bismuth particles do not follow Archard's wear law and the wear vs load graph shows a non-linear behaviour. The results are discussed in terms of known mechanisms of the coefficient of friction and wear. Chapter 7 gives the salient conclusions while in Chapter 8 we discuss some of the unanswered questions and the potential for future work in this field.
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Mirzababaei, Saereh. "IMPACT OF HUMIDITY ON WEAR AND CREEP GROAN OF AUTOMOTIVE BRAKE FRICTION MATERIALS." OpenSIUC, 2016. https://opensiuc.lib.siu.edu/theses/2056.
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In recent decades, significant requirements of changes in composition of brake friction materials in order for faster and more reliable transportation as well as their environmental friendly characterizations attracted attentions. However, the relation between performance and formulation/composition is not clear since friction processes are accompanied by many complex problems such as instability in the coefficient of friction, noise, vibration and wear. Creep-groan is a low frequency vibration which could originate in different part of the system (vehicle). The resulting resonant vibration in the passenger compartment causes discomfort and often leads to complaints of customers and related increase of warranty costs covered by manufacturers. In spite of relatively large amount of publications addressing the creep-groan phenomena, there is not an universal solution addressing the engineering aspects of brake/vehicle design. In addition, Relevance of wear occurring in brake materials increased particularly with relation to the released chemicals and corresponding health and environmental hazards. It is well known that humidity can considerably modify the adhesion of rubbing counterfaces by creating menisci and increasing the contact area. The chemistry, morphology and phase composition of the friction layers (third body) generated on the friction surfaces could play a determining role when amounts of adsorbed water on brake surfaces is concerned. The friction layer is typically a complex mix of numerous materials and, as a rule, contains the agglomerated or sintered nanoparticles. Hence, quantum effects could further modify the adsorption of water. This work addresses the impact of humidity on wear and creep groan of two commercial brake material types: the so called i) "non-asbestos organic" (NAO) and the ii) "semi-metallic" (SM) brake materials rubbed against pearlitic gray cast iron rotors typically used in the passenger vehicles. The friction and wear tests were performed with the Universal Mechanical Tester (UMT) manufactured by Bruker and the wear surfaces/mechanisms were studied by using of scanning electron microscopy, energy dispersive X-ray microanalysis, and optical topography methods. The applied wear testing conditions were designed as a series of particularly designed drag tests and were performed at several different relative humidity levels ranging between 50% and 80%. The major findings confirmed the considerable effect of humidity on wear of brake materials. Both pad types wore noticeably less at increased humidity. This was ascribed to a better capacity to form a protective friction layer. The complex wear mechanisms including abrasive, adhesive, fatigue, and corrosion wear were observed on both material types, irrespectively of humidity levels, and they dependent on the chemistry and phase composition of the friction layer. Humidity also influenced the level of friction.
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Kucuk, Taylan. "Wear Of A Mica-containing Glass-ceramic." Master's thesis, METU, 2003. http://etd.lib.metu.edu.tr/upload/4/1060920/index.pdf.
Full textAbstract:
Tribological properties of a mica glass-ceramic designed for use in dental
applications were assessed experimentally in accord with the ASTM pin on disk technique. The glass ceramic was produced through controlled
crystallization of the glass in the system SiO2, Al2O3, CaO, MgO, K2O, and F.
Crystallization was accomplished by subjecting the parent glass to a regulated
heat treatment that resulted in the nucleation and growth of crystal phases
formed in the glass.
The tests were conducted by sliding a zirconia ball against the glass and glass
ceramic disk. The friction coefficient and wear rate were determined as
functions of the applied load, sliding speed and sliding time in ambient
laboratory conditions and in acidic and basic solutions. The friction coefficient
was monitored during the tests. The wear volumes determined from surface
profile traces obtained on the wear tracks after completion of the tests were
used for calculation of the wear rates. The wear rates increased with increasing
applied load and sliding speed but decreased with increasing sliding distance.
Results were correlated with the tribological properties of the parent glass, and tribological properties of selected glasses, glass-ceramics and ceramics reported in the literature.
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Hernandez, Sinuhe. "High Temperature Wear Processes." Licentiate thesis, Luleå tekniska universitet, Maskinelement, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-16827.
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Moving machine assemblies are increasingly exposed to extreme operating conditions involving high temperatures owing to demands on higher power densities, high performance/efficiency and extreme environments. The changes in surface and near surface properties of contacting surfaces caused by exposure to high temperature and deformation govern the occurrence of friction, wear and material transfer of the tribological system. However, these changes have not been thoroughly investigated. In order to enable development of new products and processes, there is a need for new knowledge pertaining to tribological phenomena occurring at elevated temperatures.One of the most commonly used engineering materials is steel as it offers a good compromise between performance and cost even at high temperatures. For example, prehardened (quenched and tempered) tool steels are commonly used in hot forming dies can also be employed in other technological applications involving elevated temperatures. Although the research pertaining to hot stamping, and high temperature tribology in general, has significantly grown during the last years there are still knowledge gaps that need to be bridged. Adhesion and abrasion have been identified as the most dominant wear mechanisms in high temperature tribological systems but the detailed understanding of the mechanisms is still inadequate.The objective of this work is therefore to obtain a deeper understanding of the tribological phenomena associated with adhesion and abrasion that takes place at high temperatures. Unidirectional sliding wear tests have been conducted in order to investigate the influence of contact pressure and temperature on the wear and friction characteristics of tool steel and boron steel pair. Tribological studies involving boron steel, tool steels and heat-treated high-Si steels in a three body abrasive environment were also carried out with a view to explore the effect of temperature on the wear rate, wear mechanisms and to correlate this with material properties like hot hardness and toughness.The results from the unidirectional sliding tests showed that the frictional behaviour of tool steel and boron steel is load and temperature dependent. In general the friction coefficient decreases as both temperature and load are increased as a result of the formation of oxide layers. At temperatures above 200 °C, the compaction and sintering of these layers led to the formation of a wear protective glaze layer. Consequently, the wear rate for both materials decreased at elevated temperatures. Additionally, a friction and wear mechanisms map was developed for the investigated materials.In the case of abrasive wear tests, the results showed that the main wear mechanism presented for each material varied with temperature. In general, a transition from micro-ploughing to a combination of micro-cutting and micro-ploughing was present. The tool steels and boron steel showed a decrease in wear rate in the range of 100 to 400 °C compared to that at room temperature. This was attributed to the toughness in case of the tool steel and the formation of a protective tribolayers for the boron steel. Above 400 °C the wear rate increased for these three materials mainly due to the recovery and recrystallization processes. The wear rate of the high-Si steels increased with testing temperature. At 500 °C, these steels had the same hardness and the differences in wear were attributed to the changes in the material toughness.Godkänd; 2014; 20140408 (sinher); Nedanstående person kommer att hålla licentiatseminarium för avläggande av teknologie licentiatexamen. Namn: Sinuhe Hernandez Ämne: Maskinelement/Machine Elements Uppsats: High Temperature Wear Processes Examinator: Professor Braham Prakash, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet Diskutant: Assoc. Prof. Ph.D; Head, Metallic Materials and Tech. Dept. Bojan Podgornik, Institute of Metals and Technology, Ljubljana, Slovenia Tid: Fredag den 16 maj 2014 kl 10.00 Plats: E231, Luleå tekniska universitet
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Öqvist, Mona. "Numerical simulations of wear." Licentiate thesis, Luleå tekniska universitet, 2000. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-26185.
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The objective of this licentiate thesis was to study the effect of tool wear for sheet metal forming tools and how the wear process can be simulated in an efficient manner. Three Papers are appended to this licentiate thesis. Paper A covers the influence of tool geometry in deep drawing. In paper B is the way of calculating with finite element analysis described. The wear of a steel cylinder oscillating against a steel plate was studied experimentally. The worn shape of the cylinder was then compared with a numerical simulation of the shape. Paper C shows how numerical simulations can be used to simulate wear of deep drawing tools. The wear of two different deep drawing tools has been investigated. The shape of the tools before and after wear have been compared as well as the stresses and strains in the formed cups.Godkänd; 2000; 20070317 (ysko)
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Done, Vamshidhar. "Numerical modeling of dry wear : Experimental study of fretting wear, fretting wear simulations with debris entrapped and industrial applications of fretting wear models." Thesis, Lyon, 2017. http://www.theses.fr/2017LYSEI137.
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De nombreux modèles numériques sont proposés dans la littérature en utilisant des méthodes d'éléments finis et d'éléments finis discrets pour étudier l'usure par frottement, ils incluent à peine l'effet des débris d'usure. Ces modèles étant coûteux en termes de calcul, simuler un grand nombre de cycles d'usure par frottement n'est pas réalisable dans la pratique. Une nouvelle méthodologie est proposée qui ne nécessite que des propriétés de matériau en vrac comme les coefficients de frottement / usure et utilise des méthodes semi-analytiques pour simuler l'usure par frottement avec des débris piégés. Dans cette approche, les débris sont supposés être attachés à l'une des surfaces pendant le processus de fretting. Les résultats obtenus à partir de cette approche ont été comparés avec des expériences de fretting. La méthode proposée permet de saisir la profondeur d'usure et la largeur des cicatrices, et les résultats sont très proches de ceux observés dans les expériences. L'assemblage des soupapes des moteurs à combustion subit une usure par frottement en raison d'un phénomène complexe impliquant une rigidité structurelle et une tribologie de contact. L'usure des soupapes a de nombreux effets néfastes sur les performances du moteur. Il provoque une récession de la soupape entraînant des changements dans les connexions du mécanisme d'entraînement de la soupape, ce qui perturbe l'ouverture et la fermeture des soupapes. Avec des normes d'émission strictes, l'utilisation de lubrifiant pour réduire la friction au contact est limitée. Si l'usure à travers la circonférence n'est pas uniforme, il y aura une fuite de gaz et le moteur donne moins de puissance. Il est nécessaire de bien comprendre la raison de l'usure des soupapes et de développer un modèle numérique capable de prédire l'usure par frottement de la soupape pour le nombre d'heures de fonctionnement donné. Des expériences ont été réalisées pour comprendre le mécanisme d'usure et calculer les coefficients d'usure qui peuvent être utilisés dans le modèle numérique. Un modèle d'usure numérique est construit qui capture la rigidité structurelle de l'ensemble de soupape et le mécanisme d'usure au contact du siègeMany numerical models are proposed in the literature using finite element and finite discrete element methods to study fretting wear, they barely include the effect of wear debris. These models being computationally expensive, simulating large number of fretting wear cycles is not practically feasible. A new methodology is proposed which needs only bulk material properties like friction/wear coefficients and uses semi-analytical methods to simulate fretting wear with entrapped debris. In this approach, debris are assumed to be attached to one of the surfaces during the fretting process. The results obtained from this approach were compared with fretting experiments. The proposed method permits to capture the wear depth and scar width, and results are very close to that observed in the experiments. Valve assembly of combustion engines undergo fretting wear due to a complex phenomenon involving structural stiffness and contact tribology. Valve wear has many detrimental effects on the engine performance. It causes valve recession leading to changes in connections of valve drive train in turn disturbing the opening and closing of valves. With stringent emission norms, usage of lubricant to reduce friction at the contact is restricted. If the wear across the circumference is not uniform, there will be leakage of gas and the engine gives lesser power output. There is a need to thoroughly understand the reason for valve wear and develop a numerical model that can predict valve fretting wear for the given number of operating hours. Experiments were performed to understand the wear mechanism and derive wear coefficients that can be used in the numerical model. A numerical wear model is built that captures structural stiffness of the valve assembly and wear mechanism at seat contact
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Mattsson, Amanda, and Malin Lindholm. "Friction and wear mechanisms of PCBN in sliding contact with tool steel." Thesis, Högskolan Dalarna, Materialteknik, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:du-5663.
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Michelberger, David James. "An investigation of the friction, wear and corrosion properties of orthodontic appliances." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1999. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ40088.pdf.
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Matharu, Channan Singh. "Friction and wear of engineering ceramics under sliding conditions at elevated temperatures." Thesis, Brunel University, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.328848.
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Marais, Gerhard. "An investigation into the role of compounds affecting friction, wear and lubricity." Diss., University of Pretoria, 2010. http://hdl.handle.net/2263/23177.
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The high frequency reciprocating rig (HFRR) is typically used to determine the lubricity of diesel fuels and has been accepted as the universal test apparatus in most countries of the world. A study was undertaken to analyse results obtained with the HFRR instrument by identifying crucial factors contributing to friction and wear mechanisms during a lubricity test under given conditions that may lead to a better understanding of test results obtained. The transient temperature distribution on a semiinfinite disk due to a circular continuous oscillatory heat source was also modelled. The model was used to calculate the contact temperature of a contact similar to what can be expected in the HFRR apparatus. For lubricated tests a mixture of n-hexadecane (cetane) as base fluid and palmitic acid as lubricity additive was used. Experimental results, including results obtained by running unlubricated (dry) tests and results obtained from literature were all considered to formulate the hypothesis that a fully functional additive film will not survive the full duration of the lubricity test, which is 75 minutes (ISO 12156-1, 2003). Friction values obtained in the experiments conducted were much higher than what is expected for boundary films formed by long chain carboxylic acids. Comparable friction values were obtained in the first few seconds of the tests, but the friction values increased indicating the destruction of the boundary film. Metal oxide lubrication dominates for the remainder of the test. Information of the exact mechanism prevailing in the crucial first few seconds of the test should be obtained by increasing the data acquisition rate of the apparatus. It is believed that junction growth through adhesion is the dominant factor in the initial stages of the test. GCxGC/TOF-MS showed the formation of hexane and heptane, which is a strong indication of the catalytic decomposition of the C16-hydrocarbons in the sample.Dissertation (MEng)--University of Pretoria, 2010.
Chemical Engineering
unrestricted
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Chitsaz-Zadeh, Majid R. "The effects of rubber modification on friction and wear of epoxy networks." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/76092.
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An epoxy resin (Epon 828) was chemically modified with two different elastomers, poly(dimethyl-co-diphenyl) siloxane (PSX) and carboxyl-terminated butadiene-acrylonitrile (CTBN), to enhance its fracture toughness. The friction and wear of specimens modified with different amounts of elastomer were investigated in a pin-on-disk wear machine. An attempt was made to correlate the fracture toughness of the epoxy material to its fatigue wear rate for experiments in which a steel ball was sliding on a modified epoxy disk. A different type of experiment, modified epoxy pin sliding on an abrasive disk, was performed to detect whether abrasive wear of modified epoxies responds differently than fatigue wear to the fracture toughness. Other experiments were performed in which the wear debris produced during sliding was blown out of the interface to study its influence on friction and wear behavior. The effect of surface morphology on friction and wear was also studied.
The results indicated that a marked improvement in fracture toughness was achieved for samples with higher elastomer content. Regardless of the type of the experiment, epoxy pin-on-abrasive disk or steel ball-on-epoxy disk, wear rates correlated positively with inverse of fracture toughness. Both friction coefficient and wear rate were found to be influenced by the removal of the wear debris, especially for samples with higher elastomer content. The friction coefficient was reduced for samples with higher elastomer content and this was attributed to the low surface energy of the elastomer. CTBN-modified epoxies exhibited lower friction coefficients than epoxies modified with polysiloxane. It was found that sample morphology had a significant effect on both friction coefficient and wear rate; the sample with approximately the same domain size but the least number of elastomeric domains exhibited the highest friction coefficient and the highest wear rate.Ph. D.