No description available.

An investigation of the effect of metal counterface composition on the tribological performance and behaviour of a PTFE filled polymer composite using surface analysis techniques. / The high specific strength, chemical resistance and processability of polymer composites have made them an attractive alternative to traditional metals and ceramics in many industries. For tribological applications, polymer composites also have the ability to eliminate the need of lubricants and lower maintenance costs. The use of carbon fiber, carbon black and polytetrefluoroethylene (PTFE) are well established in the literature as effective reinforcement agents and solid lubricants respectively but not many studies have explored the tribochemical interactions that occurs during sliding. This study investigates the tribochemical interactions between a polyphenylene ether (PPE) and high impact polystyrene (HIPS) blend based composite and different metal surfaces. Four common metals used in industry were chosen for this study: carbon steel C1018, naval brass 485, Inconel 625 and stainless steel 316. In order to isolate the effect of tribochemical interactions between the polymer composite and counterface metals, consistent pressure and velocity (PV) settings were used for all tests. Frictional forces and temperature data were recorded during testing and the wear rates were determined by weighing samples before and after testing. The polymer sand metal washer surfaces were then examined under scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) for their PTFE surface morphology and transfer film composition, respectively. The surface roughness of both polymer and metal samples were also measured. It was observed that tribological performance of the polymer composite was affected by the composition of the metal counterface, and each metal had a different tendency to operating in a stable and unstable state. The surface morphology of the PTFE phase and the transfer film composition on the metal washers also differed between each polymer-metal system. SEM micrographs reveal agglomeration of PTFE domains on the polymer surface and each system had a different domain size distribution and PTFE surface coverage. The polymer-brass system was found to be the most consistent and give the most stable operations with the highest PTFE coverage on the polymer sample’s surface due to brass’ relatively high reactivity. This was explained by tribochemical reaction that occurs at the interface and the reactivity of each metal alloy. Adhesion must be high in order to enable a thicker and more uniform transfer film to adhere, which provides a smooth asperity-free surface for the polymer to slide against, resulting in a stable and low wear operation. A reactive interface allows the introduction of carboxyl groups on both the surfaces and increase electrostatic adhesion between the polymer transfer film and metal surface. Overall, the reactivity of each metal alloy correlated well with the number of stable tests that each polymer-metal system demonstrated as well as the resulting surface coverage of PTFE. This was taken as evidence of the tribochemical interactions. / Thesis / Master of Applied Science (MASc) / The field of friction, wear and lubrication, also known as tribology, traditionally focuses on metal and ceramic components that have high maintenance and lubrication costs. In recent years, there has been growing interest in plastic composites as a replacement material for tribological applications. The high strength, light weight, chemical resistance and self-lubricating properties of these plastic composites makes them an attractive substitute for metals and ceramics. Understanding the chemical interaction between plastic and metal during sliding is necessary to exploit their properties and performance for specific applications. In this study, a plastic composite based on a blend of polyphenylene ether (PPE) and high impact polystyrene (HIPS) filled with polytetrafluoroethlyene (PTFE), carbon black and carbon fiber was used to investigate the effects of different metals on tribological performance and behaviour. Four common metals used in industry were chosen for this study: carbon steel C1018, naval brass 485, Inconel 625 and stainless steel 316. The tribology tests conclusively showed that friction and wear results differ between polymer-metals systems, with each system displaying a stable and unstable behaviour. Surface analysis revealed that the surface PTFE morphology of the polymer composite and the transfer film composition on the metal washer also differ between metals. Tribochemical reactions and the reactivity of each metal explained the results and behaviour of each polymer-metal system.

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.

In most of the tribological experiments studying friction and wear behaviour, the contact interface is hidden. The present work attempts to overcome this hidden-interface problem by carrying out real-time tribological experiments inside Transmission Electron Microscope (TEM). This is achieved by developing an in situ TEM triboprobe which can carry out nanoscale indentation, sliding and reciprocating tests on an electron transparent sample inside TEM. A novel in situ TEM triboprobe is developed by characterising the individual components involved in the development. Coarse positioning of a sharp probe is achieved using inertial sliders. Fine motion of the probe is controlled using a 4-quadrant tube piezoceramic. This triboprobe is capable of carrying out high stiffness tribological experiments inside TEM. The interface is viewed at high resolutions in real time during the experiments using a movie rate CCD camera. In indentation experiments a sharp probe is brought into contact with the sample surface. During indentation of Aluminium alloy tribolayer, it has been observed that the cracks originate from subsurface and propagate to the surface causing delamination-like material removal. Indentation experiments on protruding silicon particle in Aluminium-Silicon (Al-Si) alloy shows that initial deformation is elastic. Once the load is increased, the particle starts indenting the soft aluminum matrix, and results in sinking of the particle into the aluminium matrix. Once the particle starts sinking, the increase in the displacement causes the generation of a crack and the propagation of this crack results in the fracture of the particle. The sliding experiments inside TEM allowed the direct visualization of asperity level interaction during sliding. The preliminary experimental results of nanoscale sliding experiments carried out using an AFM tip as the sample. The adhesive instability is observed as snap-in and snap-out events. The snap-out distance seems to depend on the local geometry of the contact. To simulate reciprocating wear, a sharp diamond probe is brought into contact with Al-Si alloy and reciprocated sinusoidally at 0.5Hz. At lower loads no wear is observed. However, when the normal load is increased, material starts getting removed in thin slivers, and most of the wear debris generated get swept away from the track. Some wear debris get entrapped in between the sliding surfaces; subsequently they join to form larger wear particles. The trapped particles generated during the test act like rollers and a significant increase in the stroke-length is observed accompanying the rolling action of the particle. The phenomena like agglomeration and dissociation of the wear particles has also been observed. Repeated deformation of the trapped particles leads to the formation of tiny liquid drop on some of the wear debris. The liquid consists of gallium which comes from the sample preparation technique. The interaction between the liquid droplets has been studied by carrying out liquid-bridge pulling experiments. Liquid gallium gets cooled with time during tensile pulling of the droplets. A nano-filament is formed between the droplets during pulling. After some time, the droplet gets solidified and coalescence of droplets does not take place. Further frictional heating was necessary to form the bridge again. The in situ TEM triboprobe, which allow the tribological processes to be observed dynamically under high resolutions, is a power full tool in detecting fundamental tribological interactions.

No description available.

Em tribossistemas pode ser necessário o controle do atrito e a minimização do desgaste dos materiais. Dentre as soluções propostas, se encontram tratamentos térmicos e termoquímicos, deposição de filmes finos e formação de revestimentos duplex. O objetivo desse trabalho é entender e comparar como variam a microestrutura, as propriedades mecânicas, o desempenho tribológico e os mecanismos de desgaste em um aço inoxidável martensítico AISI 440B após os tratamentos de i) têmpera e ii) nitretação a plasma pulsada. A caracterização da microestrutura consistiu na identificação das fases por difração de raios - X, observação por microscopia ótica e por MEV-FEG. A caracterização das propriedades mecânicas consistiu em medições de dureza Rockwell C e microdureza Vickers (carga de 100gf). Por fim, o desempenho tribológico e os mecanismos de desgaste foram avaliados através de: a) determinação dos parâmetros de rugosidade por rugosimetria e AFM; b) levantamento das curvas de coeficiente de atrito vs. tempo através do ensaio de desgaste linear cíclico (SRV) sem lubrificação; c) perda de massa dos discos e esferas; d) observação das trilhas de desgaste e das calotas de desgaste por meio de MEV-FEG/EDS; e) levantamento do perfil topográfico da superfície dos discos desgastados e f) profundidade das trilhas através de interferometria ótica. Obteve-se microestrutura da camada nitretada constituída de martensita revenida e nitretos ?\', ? e CrN. A camada nitretada apresentou dureza máxima de 1340 HV0,1 e profundidade de camada NHT de ~100µm. Durante a nitretação a matriz martensítica sofreu revenimento que diminuiu a dureza de 54 HRC (temperado) para 50 HRC. Constatou-se que no tribossistema \"deslizamento a seco entre esfera de AISI 52100 e disco de AISI 440B Temperado\", ocorreram no corpo: i) deformação plástica, ii) abrasão de 3 corpos nas extremidades das trilhas, iii) desgaste oxidativo e iv) delaminação (arrancamento do filme óxido). Já no contra-corpo: i) abrasão suave e ii) adesão de debris óxidos. No tribossistema \"deslizamento a seco de esfera de AISI 52100 contra disco de AISI 440B Nitretado\" ocorreram no corpo: i) microcutting, ii) desgaste oxidativo e iii) delaminação (arrancamento de asperezas e/ou de filme óxido). Já no contra-corpo: i) abrasão severa e ii) adesão de debris óxidos. / In tribosystems to control friction and wear is necessary. Several solutions have been developed over the last few years, such as heat treatments, thermo-chemical treatments, thin films deposition and duplex coatings. The purpose of the present work is to understand how the microstructure, mechanical and tribological properties of AISI 440B vary after being subjected to the following treatments i) quenching, ii) plasma nitriding. The approach to study AISI 440B microstructure consisted of XRD (X-Ray Diffraction), optical microscopy and SEM (Scanning electron microscopy). The approach to study AISI 440B mechanical properties consisted of Rockwell C hardness and Vickers microhardness. Finally, the approach to study AISI 440B tribological performance was: a) surface and roughness observations through contact rugosimetry and AFM, b) friction coefficient vs. time curves through unlubricated reciprocating tribological test (ASTM G133-05), c) disc and sphere mass loss, d) wear track and wear cap observations through SEM-FEG/EDS, e) surface profile and wear track depth through optical interferomety. The nitrided layer presented tempered martensite as well as ?, ? and CrN nitrides. The maximum surface hardness was 1340 HV 0,1 and a case depth of ~100 µm was found. Regarding the wear mechanisms, in the \"dry sliding of AISI 52100 sphere against as-quenched AISI 440B discs\" tribosystem, the wear mechanisms acting in the body were: severe wear with i) severe plastic deformation, ii) 3-body abrasion at the ends of the wear tracks, iii) oxidation, and iv) mild delamination (oxide pull-out). Regarding the counterbody, it was found: i) mild abrasion and ii) oxide adhesion. In the \"dry sliding plasma nitrided AISI 440B against AISI 52100 spheres\" tribosystem the body suffered mild wear with i) oxidation and ii) delamination. The counterbody suffered i) strong abrasion and ii) oxide adhesion.

This thesis is concerned with issues relating to the development of an active sealing system for hydraulic actuators where the sealing elements can be radially extended and retracted to vary the friction and leakage characteristics. In order to determine the feasibility of the active sealing concept it is necessary to establish that varying the seal geometry may achieve useful improvements in the friction-leakage trade-off and that a practical method of achieving this seal extension can be realised. Experimental and simulation approaches for seal friction prediction have been developed and active seal prototypes produced to demonstrate the concept. <br /> Experiments were carried out to measure the constant velocity friction for single-lip and double-lip seals over a range of sliding speeds and sealed pressures with special consideration applied to the instroke-outstroke direction dependence. Additional experiments were performed with sinusoid motion to provide an indication of the transient friction characteristics. Friction was shown to increase towards the end of the outstroke cycle and decrease once the instroke motion began. <br /> Tribology simulations were produced based on the results of a FEA simulation of the rod-seal contact pressure. Empirical friction-load relationships and novel contact mechanics approaches for high loads were considered. Simulations based on the Reynolds equation including standard inverse EHL theory and the GW-average Reynolds lubrication are also presented. Experimental agreement could be improved if loading is assumed to transfer to the fluid to maintain a fluid film. A hysteresis friction model was also developed in attempt to improve the prediction of speed dependent friction. <br /> Two active seal prototypes were produced, each with an adjustable external pressure supplied to the outer circumference of the sealing element. Constant velocity friction measurements for different external pressures and the transient response following step changes in this pressure are presented.

The synovium is a specialized connective tissue that encapsulates diarthrodial joints like the knee, maintaining a low-friction environment for the articulating surfaces within. This tissue plays a key role in homeostasis by regulating solute transport in and out of the joint, and secreting lubricating factors into the synovial fluid. The predominant cell type in the synovium is the fibroblast-like synoviocyte (FLS), which resides on the intimal surface of the tissue and produces lubricating molecules such as hyaluronan. Because these cells directly face the synovial fluid and apposing tissue surfaces within the joint, they are exposed to a dynamic environment of mechanical stimuli generated during daily activity. This dissertation addresses the global hypothesis that FLS are mechanosensitive to distinct modes of shear stress generated in the knee during articulation, and that modulation of this sensitivity by chemical and physical factors of the osteoarthritic (OA) environment contributes to disease progression. Previous work has demonstrated that fluid-induced shear stress, generated as synovial fluid redistributes within the capsule during articulation, is a relevant mechanical stimulus for FLS. Exposure of FLS to fluid shear has been shown to modulate downstream functions such as lubricant secretion and the release of degradative matrix-metalloproteinases as induced by the cytokine interleukin-1 (IL-1), the latter indicating a link between mechanotransduction and the inflammatory environment of OA. The first goal of this dissertation was to further elucidate FLS mechanotransduction by characterizing the upstream response of FLS to fluid shear and determine the influence of IL-1 thereupon. The work presented herein demonstrates for the first time a robust calcium signaling response of FLS to fluid shear, a key upstream event in the mechanotransduction of physical stimuli. Key aspects of this response were significantly altered by pre-exposure to IL-1, indicating a pathologic modulation of normal mechanosensing in the OA environment. This effect was observed across bovine and human models and was found to be potentiated by both increasing intercellular communication and modulation of cell primary cilia. In addition to chemical factors such as cytokines, the degradation of cartilage during OA produces a physical factor that perpetuates disease state in the form of cartilage wear particles (CWP). These particles are released into the synovial fluid and attach directly to the synovium. We have previously shown that CWP induce FLS monolayers to release pro-inflammatory mediators of OA. The second goal of this dissertation was to investigate the effect of CWP on both cell-level function and tissue-level properties. To this end we showed first that CWP modulate the calcium signaling response of FLS to fluid shear in a contact dependent manner, and that inhibition of intercellular communication is a potential mechanism of this effect. In areas of the articulating capsule where apposing tissues slide in direct contact with each other, contact-induced shear stress provides another relevant physical stimulus to FLS. In this case of direct interaction between surfaces, the tissue-level frictional properties may affect the magnitude of shear stress presented to the cells within the intimal layer and thus influence mechanotransduction. A novel bioreactor was developed to characterize the effect of sliding contact on downstream functions of FLS within explant tissues. An increase in metabolic activity with culture under these conditions suggests that contact shear is a relevant stimulus for FLS. While previous work has characterized synovium friction properties in sliding contact against glass, relatively little is known of synovium tribology in native tissue configurations, or the influence of pathologic conditions such as CWP attachment. This dissertation reports for the first time low friction properties for synovium against other tissues within the joint such as cartilage and demonstrates a significant deleterious effect of CWP on these properties. The research presented in this dissertation further elucidates the processes of normal synoviocyte mechanotransduction, and by demonstrating that key chemical and physical factors of the OA environment modulate both cell and tissue-level functional properties, sheds light on the mechanisms by which the synovium contributes to disease progression. This sets the foundation for future work into synovium mechanotransduction of distinct physical stimuli and the relationship with tissue-level mechanical properties, and points towards clinical interventions that seek to restore the normal mechanical environment of the joint.

Em tribossistemas pode ser necessário o controle do atrito e a minimização do desgaste dos materiais. Dentre as soluções propostas, se encontram tratamentos térmicos e termoquímicos, deposição de filmes finos e formação de revestimentos duplex. O objetivo desse trabalho é entender e comparar como variam a microestrutura, as propriedades mecânicas, o desempenho tribológico e os mecanismos de desgaste em um aço inoxidável martensítico AISI 440B após os tratamentos de i) têmpera e ii) nitretação a plasma pulsada. A caracterização da microestrutura consistiu na identificação das fases por difração de raios - X, observação por microscopia ótica e por MEV-FEG. A caracterização das propriedades mecânicas consistiu em medições de dureza Rockwell C e microdureza Vickers (carga de 100gf). Por fim, o desempenho tribológico e os mecanismos de desgaste foram avaliados através de: a) determinação dos parâmetros de rugosidade por rugosimetria e AFM; b) levantamento das curvas de coeficiente de atrito vs. tempo através do ensaio de desgaste linear cíclico (SRV) sem lubrificação; c) perda de massa dos discos e esferas; d) observação das trilhas de desgaste e das calotas de desgaste por meio de MEV-FEG/EDS; e) levantamento do perfil topográfico da superfície dos discos desgastados e f) profundidade das trilhas através de interferometria ótica. Obteve-se microestrutura da camada nitretada constituída de martensita revenida e nitretos ?\', ? e CrN. A camada nitretada apresentou dureza máxima de 1340 HV0,1 e profundidade de camada NHT de ~100µm. Durante a nitretação a matriz martensítica sofreu revenimento que diminuiu a dureza de 54 HRC (temperado) para 50 HRC. Constatou-se que no tribossistema \"deslizamento a seco entre esfera de AISI 52100 e disco de AISI 440B Temperado\", ocorreram no corpo: i) deformação plástica, ii) abrasão de 3 corpos nas extremidades das trilhas, iii) desgaste oxidativo e iv) delaminação (arrancamento do filme óxido). Já no contra-corpo: i) abrasão suave e ii) adesão de debris óxidos. No tribossistema \"deslizamento a seco de esfera de AISI 52100 contra disco de AISI 440B Nitretado\" ocorreram no corpo: i) microcutting, ii) desgaste oxidativo e iii) delaminação (arrancamento de asperezas e/ou de filme óxido). Já no contra-corpo: i) abrasão severa e ii) adesão de debris óxidos. / In tribosystems to control friction and wear is necessary. Several solutions have been developed over the last few years, such as heat treatments, thermo-chemical treatments, thin films deposition and duplex coatings. The purpose of the present work is to understand how the microstructure, mechanical and tribological properties of AISI 440B vary after being subjected to the following treatments i) quenching, ii) plasma nitriding. The approach to study AISI 440B microstructure consisted of XRD (X-Ray Diffraction), optical microscopy and SEM (Scanning electron microscopy). The approach to study AISI 440B mechanical properties consisted of Rockwell C hardness and Vickers microhardness. Finally, the approach to study AISI 440B tribological performance was: a) surface and roughness observations through contact rugosimetry and AFM, b) friction coefficient vs. time curves through unlubricated reciprocating tribological test (ASTM G133-05), c) disc and sphere mass loss, d) wear track and wear cap observations through SEM-FEG/EDS, e) surface profile and wear track depth through optical interferomety. The nitrided layer presented tempered martensite as well as ?, ? and CrN nitrides. The maximum surface hardness was 1340 HV 0,1 and a case depth of ~100 µm was found. Regarding the wear mechanisms, in the \"dry sliding of AISI 52100 sphere against as-quenched AISI 440B discs\" tribosystem, the wear mechanisms acting in the body were: severe wear with i) severe plastic deformation, ii) 3-body abrasion at the ends of the wear tracks, iii) oxidation, and iv) mild delamination (oxide pull-out). Regarding the counterbody, it was found: i) mild abrasion and ii) oxide adhesion. In the \"dry sliding plasma nitrided AISI 440B against AISI 52100 spheres\" tribosystem the body suffered mild wear with i) oxidation and ii) delamination. The counterbody suffered i) strong abrasion and ii) oxide adhesion.

In the current work, two different coatings, nitrocarburised (CN) and titanium carbonitride (TiCN) on M2 grade high speed tool steel, were prepared by commercial diffusion and physical vapour deposition (PVD) techniques, respectively. Properties of the coating were characterised using a variety of techniques such as Glow-Discharge Optical Emission Spectrometry (GD-OES) and Scanning Electron Microscopy (SEM). Three non-commercial, oil-based lubricants with simplified formulations were used for this study. A tribological test was developed in which two nominally geometrically-identical crossed cylinders slide over each other under selected test conditions. This test was used to evaluate the effectiveness of a pre-applied lubricant film and a surface coating for various conditions of sliding wear. Engineered surface coatings can significantly improve wear resistance of the tool surface but their sliding wear performances strongly depend on the type of coating and lubricant combination used. These coating-lubricant interactions can also have a very strong effect on the useful life of the lubricant in a tribological system. Better performance of lubricants during the sliding wear testing was achieved hen used with the nitrocarburised (CN) coating. To understand the nature of the interactions and their possible effects on the coating-lubricant system, several surface analysis techniques were used. The molecular level investigation of Fourier Transform Infrared Spectroscopy (FTIR) revealed that oxidative degradation occurred in all used oil-based lubricants during the sliding wear test but the degradation behaviour of oil-based lubricants varied with the coating-lubricant system and the wear conditions. The main differences in the carbonyl oxidation region of the FTIR spectra (1900-1600 cm-1) between different coating-lubricant systems may relate to the effective lifetime of the lubricant during the sliding wear test. Secondary Ion Mass Spectrometry (SIMS) depth profiling shows that the CN coating has the highest lubricant absorbability among the tested tool surfaces. Diffusion of chlorine (C1), hydrogen (H) and oxygen (O) into the surface of subsurface of the tool suggested that strong interactions occurred between lubricant and tool surface during the sliding wear test. The possible effects of the interactions on the performance of whole tribological system are also discussed. The study of Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) indicated that the envelope of hydrocarbons (CmHn) of oil lubricant in the positive TOF-SIMS spectra shifted to lower mass fragment after the sliding wear testing due to the breakage of long-chain hydrocarbons to short-chain ones during the degradation of lubricant. The shift of the mass fragment range of the hydrocarbon (CmHn) envelope caries with the type of both tool surface and lubricant, again confirming that variation in the performance of the tool-lubricant system relates to the changes in surface chemistry due to tribochemical interactions at the tool-lubricant interface under sliding wear conditions. The sliding wear conditions resulted in changes not only in topography of the tool surface due to mechanical interactions, as outlined in Chapter 5, but also in surface chemistry due to tribochemical interactions, as discussed in Chapters 6 and 7.