Dissertation submitted in compliance with the requirements for the Master's Diploma in Technology: Mechanical Engineering, Technikon Natal, 1994. / This dissertation is concerned with the construction of the locally developed Ferro-precipitator which can be utilised outside a laboratory environment. The American developed Ferrograph machine, besides being expensive (R42 000 + GST in 1984), can only be used inside a dust free, temperature controlled room. As lubricants in machinery moving parts play an important role in their performance and durability many methods of evaluating the health of machines have been devised, but none by themselves can give a complete picture of what is happening inside the machine. Various methods of oil analysis have been studied in this dissertation for comparison and/or complementary purposes, so as to establish the role of the Ferro-precipitator in the context mentioned. Spectrometric, Debris and Radio Tracer methods are based on quantitative aspects of wear particle analysis, whereas the Magnetic Plug method shows visibly large wear particles in the very high wear pattern range. A further aspect to consider is the fact that the Spectrometric analysis method, which is the most common and comprehensive method available in South Africa, is laboratory orientated. This means that an oil sample has to be taken from a machine and then sent to a laboatory for analysis. Besides being time consuming from the time the samples are taken to the time when the results are known, the Spectrometric analysis method is also very expensive. The Ferro-precipitator that has been developed, is sensitive to particle size and to the rate at which these particles are generated. This is due to the phenomenon that a varying magnetic field strength will attract different size ferrous particles accordingly. This concept was validated by manufacturing ferrous particles of various sizes, firstly by grinding and secondly by sieving. These particles, in both cases, were passed through the Ferro-precipitator in a medium of oil, and graphs of density versus distance along the slide were plotted. The graphs showed distinct variations between particle sizes. The manufactured particles were also statistically evaluated by establishing the correlation between the machined and/or the sieved particles to the optically measured particles. The sensitivity of the Ferro-precipitator was further demonstrated by comparing results obtained from an engine test carried out under controlled conditions using the Spectrometric method. If developed further, the Ferro-precipitator .could, be used in the field, which would eliminate the time lost due to samples being sent ot a laboratory. Also the cost of the machine would be a fraction of the price of the Ferrograph and/or the Spectrometer. An in-depth study of particle morphology can be carried out on the wear particles deposited on the slide, with the aid of a Scanning Electron microscope using its X-Ray attachment. The potential for such a study was demonstrated on the engine test performed for this dissertation. / M

Thesis (Ph. D.)--Ohio State University, 2004. / Title from first page of PDF file. Document formatted into pages; contains xix, 188 p.; also includes graphics. Includes bibliographical references (p. 179-188).

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Lead (Pb) containing alloys such as white metals and Cu-Pb-Sn (lining) with Pb-based overlay plating have been extensively used as materials for internal combustion engine bearings during the last several decades. However, owing to environmental and health concerns, the use of Pb containing materials in automotive engine components is being restricted. In view of this, attempts are under way to develop and replace Pb-containing materials with Pb–free bearing materials. The tribological characteristics of these recently developed Pb-free bearing materials have, however, not been fully investigated and only a limited results about their tribological performance are available in open literature. This thesis therefore focuses on investigating the tribological performance of some recently developed Pb-free engine bearing materials. Although engine bearings are designed to operate in full film lubrication conditions yet they also operate in mixed and boundary lubrication regimes where the material properties do affect their tribological performance. There is thus a need to study the tribological behaviour of these new Pb-free bearing materials in mixed and boundary lubrication conditions vis a vis that of conventional Pb-containing bearing linings and overlays. This work has therefore aimed at investigating the tribological characteristics such as friction and wear, seizure behaviour, interaction with different oil formulations and embeddability behaviour of some selected Pb-free engine bearing materials. Friction and wear properties of Pb-free bearing materials Al-Sn based lining without overlay, bronze lining coated with Polyamide-Imide (PAI) based overlay containing MoS2 and graphite, bronze lining coated with Al-Sn based and PAI based overlay containing MoS2 and graphite, bronze lining coated with Sn-based overlay, and bismuth (Bi) containing bronze lining coated with Sn-based overlay have been studied using a block-on-ring test configuration under unidirectional sliding conditions in mixed and boundary lubrication regimes. The conventional Pb-containing bearing material was also studied as a reference material. Al-Sn based material showed considerably higher friction compared to the other bearing materials. The bearing material with PAI based overlay containing MoS2 and graphite showed superior friction and wear properties compared to all other materials. Sn-based overlay coated materials resulted in comparable friction and wear properties to that of Pbbased overlay. Wear mechanism in Al-Sn based material is mainly adhesive and abrasive in case of Sn based overlay. Seizure behaviour of the bearing materials were also studied using the block-on-ring test configuration in dry as well as lubricated conditions using pure base oil and a fully formulated engine oil. The PAI based overlay containing MoS2 and graphite showed no sign of seizure even at the highest test load in dry as well as lubricated conditions. Al-Sn based lining without overlay seizes at relatively lower load in dry condition compared to the other bearing materials. Adhesion or wear debris smearing onto the counter surface is the main causes of seizure in dry condition. In lubricated condition, seizure occurred at relatively higher load and the conventional Pb-containing material was found to have better seizure performance compared to the Al-Sn based and Sn-based overlay plated materials. Tribological compatibility of Pb-free bearing materials with different oil formulations was studied using a ball-on-bearing specimen test configuration in boundary lubrication under reciprocating sliding conditions. Four different bearing materials were investigated using different lubricants with and without oil additives. In general, the bearing materials lubricated with pure PAO base oil showed higher friction compared to those lubricated with oils containing additives. Lubricants containing additives improved wear properties of the bearing materials except in the case of Al-Sn based lining without overlay. It was also observed that the anti-wear additive level did not significantly influence the wear performance of bearing overlays. The embeddability behaviour of Pb-free bearing materials was studied using a fully formulated engine oil contaminated with SiC particles. Pb-free bearing materials with Snbased overlay, Bi-based overlay, PAI-based overlay containing MoS2 and composite overlay containing PAI, Al, PTFE were investigated. Tests at different rotational speeds (i.e. different oil film thickness) and a constant load were carried out using a journal bearing test rig. It was found that material removal from bearing and shaft surfaces due to abrasive wear is influenced by the lubricant film thickness. The steel counter surface showed lower wear in tests using Sn based overlay and a PAI, Al and PTFE containing composite overlay compared to Bi-based overlay and PAI-based overlay containing MoS2.

With today’s striving towards reduction of fuel consumption it is moreimportant than ever to understand the function of different componentsin the internal combustion engine. There is a need to develop and usetools to investigate and predict the result of specific design changesmade on the components. In this work, the mechanics and the tribologyof the power cylinder unit and more specifically the operation of thepiston rings was investigated both numerically and experimentally. Theobjectives of the numerical part of this thesis were to develop simulationtools that can be used to quantify design changes to the TLOCR andthe cylinder liner. Such as the dimensions of the ring itself but also ringtension, running land profile, out of roundness of the cylinder liner andsurface texture of dimple type applied on the cylinder liner. Numericalsimulation models were developed and used to investigate operation of atwin land oil control ring (TLOCR). TLOCR are typically used in heavyduty diesel engines (HDDE). The TLOCR plays a very important role inthe engine since it is supposed to distribute the correct amount of oil onthe liner to lubricate the other rings. It is important that the TLOCRdoes not leave too much oil on the liner for the two top rings since itcould lead too high oil consumption. In a HDDE the piston assemblyis the largest contributor to frictional losses where the piston ring packaccounts for the major part of this. The oil control ring is the largestcontributor to frictional losses in the piston ring pack therefore makingit very interesting to study from a fuel consumption perspective. One ofthe models developed in this work accounts for the tribological interfaceof the TLOCR against the cylinder liner and piston ring groove as wellas the elastic deformation of the ring and the ring dynamics within thepiston ring groove. The actual ring cross section was modelled in orderto account for the full three dimensional elastic deformation of the ring.By solving all of these problems as a coupled system, the entire operation of the oil control ring can be understood in a better way than earlierand this opens up new optimisation possibilities for the TLOCR. Sincethe cylinder liner in an engine will always have some deviation fromperfectly round this is important. The full ring is modelled in order toaccount for out of round cylinder liners. The model can therefore beused to investigate the effect on oil distribution by reduced ring tensionwhich will affect the frictional losses of the system. It was found that thereduction in tangential force on the TLOCR with kept sealing capability,enabled by reduced out-of-roundness, could result in friction reductionof 40 % at mid-stroke.Because of the complexity, a multi-physics model of this type introducesdifficulties with convergence. Especially when implementinga mass conserving cavitation model and solving for the reversal of thepiston ring. Implementation and numerical verification of a mass conservingcavitation model was therefore performed. A method for dealingwith the convergence problem close to reversal was implemented and discussed.A model considering texture, of dimple type, on the cylinder linerwas also developed to find dimple dimensions optimal for reduced fuelconsumption. Since the dimples are modelled in a deterministic manner,only a periodic section of one land of the TLOCR was considered. Themodel takes mixed lubrication and inertia of the ring into considerationand a mass conserving cavitation algorithm were implemented. Theresults from the model predict friction reduction of approximately 40 %at mid-stroke speeds.The objective of the experimental part of this thesis is to developa novel test method for evaluation of piston ring friction at realisticspeeds. The test-rig was designed and constructed during the first halfof the project. The rig was designed so that standard HDDE productionpiston rings and cylinder liners could be easily mounted, and so thatpiston ring friction could be measured without influence from pistonfriction. Both cylinder liner and oil tank were equipped with heaters,where the oil supply resembles that in an actual engine. Repeatabilityof the results was found to be good. Influence on friction by differentcylinder liner surface roughness and coatings were investigated. Variouspiston ring designs, ring tension and coatings were also investigated. Itwas found that friction of the TLOCR could be reduced with close to50 % with kept sealing capability by reduced ring tension and differentgeometry on the lands in contact with the cylinder liner. The numerical simulation model governing the full cross section of the TLOCR wasvalidated against measured piston ring friction data at a number ofdifferent speeds and excellent correlation was found.

This research investigates materials for bone-joint failure repair using tribological and biomimicking approaches. The materials investigated represent three different repairing strategies. Refractory metals with and without treatment are candidates for total joint replacements due to their mechanical strength, high corrosion resistance and biocompatibility. A composite of biodegradable polytrimethylene carbonate, hydroxyl apatite, and nanotubes was investigated for application as a tissue engineering scaffold. Non-biodegradable polymer polyimide combined with various concentrations of nanotubes was investigated as a cartilage replacement material. A series of experimental approaches were used in this research. These include analysis of material surfaces and debris using high-resolution techniques and tribological experiments, as well as evaluation of nanomechanical properties. Specifically, the surface structure and wear mechanisms were investigated using a scanning electron microscope and an atomic force microscope. Debris morphology and structure was investigated using a transmission electron microscope. The debris composition was analyzed using an X-ray diffractometer. Nanoindentation was incorporated to investigate the surface nanomechanical properties. Polytrimythelene carbonate combined with hydroxyapatite and nanotubes exhibited a friction coefficient lower than UHMWPE. The nanoindentation response mimicked cartilage more closely than UHMWPE. A composite formed with PI and nanotubes showed a varying friction coefficient and varying nanoindentation response with variation in nanotube concentration. Low friction coefficients corresponded with low modulus values. A theory was proposed to explain this behavior based on surface interactions between nanotubes and between nanotubes and PI. A model was developed to simulate the modulus as a function of nanotube concentration. The boronized refractory metals exhibited brittleness and cracking. Higher friction coefficients were associated with the formation of amorphous debris. The friction coefficient for boronized Cr (~0.06) under simulated body fluid conditions was in the range found in natural joints.

This research investigates materials for bone-joint failure repair using tribological and biomimicking approaches. The materials investigated represent three different repairing strategies. Refractory metals with and without treatment are candidates for total joint replacements due to their mechanical strength, high corrosion resistance and biocompatibility. A composite of biodegradable polytrimethylene carbonate, hydroxyl apatite, and nanotubes was investigated for application as a tissue engineering scaffold. Non-biodegradable polymer polyimide combined with various concentrations of nanotubes was investigated as a cartilage replacement material. A series of experimental approaches were used in this research. These include analysis of material surfaces and debris using high-resolution techniques and tribological experiments, as well as evaluation of nanomechanical properties. Specifically, the surface structure and wear mechanisms were investigated using a scanning electron microscope and an atomic force microscope. Debris morphology and structure was investigated using a transmission electron microscope. The debris composition was analyzed using an X-ray diffractometer. Nanoindentation was incorporated to investigate the surface nanomechanical properties. Polytrimythelene carbonate combined with hydroxyapatite and nanotubes exhibited a friction coefficient lower than UHMWPE. The nanoindentation response mimicked cartilage more closely than UHMWPE. A composite formed with PI and nanotubes showed a varying friction coefficient and varying nanoindentation response with variation in nanotube concentration. Low friction coefficients corresponded with low modulus values. A theory was proposed to explain this behavior based on surface interactions between nanotubes and between nanotubes and PI. A model was developed to simulate the modulus as a function of nanotube concentration. The boronized refractory metals exhibited brittleness and cracking. Higher friction coefficients were associated with the formation of amorphous debris. The friction coefficient for boronized Cr (~0.06) under simulated body fluid conditions was in the range found in natural joints.

Mechanical forces can be used to trigger chemical reactions through activating bonds and to direct the course of such reactions in organic materials, particularly in polymers. In inorganic materials, the small molecules present significant challenges in directing the reaction kinetics. This dissertation studied the dynamics and kinetics of oxidation of transitional metals, particularly on tantalum through mechanical forces. This is a new area of research in surface science. Experimentally using a combined electrochemical and mechanical manipulation technique, we compared the equilibrium and non-equilibrium oxidation processes and states of tantalum. An experimental setup was developed with an electrochemical system attached to a sliding mechanical configuration capable of friction force measurement. The surface chemistry of a sliding surface, i.e., tantalum, was controlled through the electrolyte. The mechanical force was fixed and the dynamics of the surface was monitored in situ through a force sensor. The formation of non-equilibrium tantalum oxides was found in fluid environments of hydrogen peroxide, acetic acid and deionized water. We found that the mechanical energy induced the non-stable state reactions leading to metal-stable oxides. Analytically, we compared the energy dispersion, reaction kinetics, and investigate physical chemical reactions. We proposed a modified Arrhenius equation to predict the effect of mechanical energy on non-spontaneous reaction under nonequilibrium conditions. At the end, we also propose a modified Pourbaix diagram known as the Kar-Liang diagram. The Kar-Liang diagram helps to understand the behavior of tantalum under non-equilibrium conditions. A complete understanding of the tribochemical reaction of tantalum is achieved through this dissertation. The dissertation contains six chapters. After the introduction and approach, oxidation of tantalum is discussed in Chapter IV, kinetics in Chapter V. The nonequilibrium Kar-Liang diagram is discussed in Chapter VI, followed by conclusion. This research has important impacts on the field of surface science in understanding the basics of mechanochemical reactions. The resulting theory is beneficial to understand chemical-mechanical planarization (CMP) and to optimize the current industrial processes in microelectronics in making integrated circuits.

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Document formatted into pages; contains xxvi, 214 p.; also includes graphics (some col.) Includes bibliographical references (p. 203-214). Available online via OhioLINK's ETD Center

Made available in DSpace on 2014-06-11T19:27:12Z (GMT). No. of bitstreams: 0 Previous issue date: 2011-01-06Bitstream added on 2014-06-13T19:55:29Z : No. of bitstreams: 1 teixeira_kd_me_guara.pdf: 3359686 bytes, checksum: 99856978cd25324653f6bcfa0f289211 (MD5) / O Ferro Fundido é amplamente utilizado na indústria de autopeças do setor automobilístico, principalmente em anéis de pistão, camisa de cilindros, discos de freios e outros, devido a sua boa resistência ao atrito e desgaste, por ter boa condutividade térmica e ser antivibracional. Com a globalização, grandes esforços vêm sendo feitos por pesquisadores, direcionados ao desenvolvimento de novos materiais que atendam os mercados mundiais, trazendo a competitividade necessária na busca de processos de fabricação e pesquisas, objetivando redução de custos, qualidade e produtividade, sendo que no ramo automobilístico a realidade não é diferente. Motores menores e mais leves têm aumentado constantemente os carregamentos térmicos e mecânicos dos componentes, na qual o sistema tribológico do anel de pistão é dos mais complexos. O objetivo deste trabalho foi avaliar o comportamento tribológico através do teste de bancada pino-disco dos pares: Ferro Fundido Cinzento Centrifugado/ Ferro Fundido Cinzento MC12 e Ferro Fundido Cinzento Centrifugado/ Ferro Fundido Cinzento MC13 em função da velocidade de deslizamento (0,5 m/s, 1,0 m/s e 1,5 m/s). Para os discos (MC 12 e MC 13) a taxa de desgaste decresceu linearmente com o aumento da velocidade de deslizamento, já para os pinos em Ferro Fundido Cinzento Centrifugado, a taxa de desgaste decresceu até 1,0 m/s, e a 1,5 m/s a taxa de desgaste apresentou um ligeiro aumento, determinado pela instabilidade gerada pelo aquecimento da superfície e formação da camada de óxido. O par Centrifugado/ MC 13 apresentou melhor desempenho a 0,5 m/s e o par Centrifugado/ MC 12 a 1,0 e 1,5 m/s. Verificou-se que os mecanismos de desgaste atuantes são: adesão (0,5 m/s), adesão + oxidação (1,0 m/s) e oxidação (1,5 m/s). Em todas as velocidades de deslizamento, os mecanismos principais de desgaste são seguidos de microabrasão / The cast iron is widely used in auto parts industry in the automotive sector, mainly in piston rings, cylinder liners, brake discs and others due to its good resistance to friction and wear, to have good thermal conductivity and be antivibrational. With globalization, great efforts have been made by researchers, directed the development of new materials that meet the global markets, bringing the competitiveness required in the pursuit of manufacturing processes and research, aiming at cost reduction, quality and productivity, and the branch automotive reality is no different. Smaller engines and lighter loads have steadily increased thermal and mechanical components, in which the tribological system piston ring is the most complex. The aim of this study was to evaluate the tribological behavior through the test bench pin-disk pairs: Centrifuged Gray Cast Iron/ Gray Cast Iron MC 12 and Centrifuged Gray Cast Iron/ MC 13 depending on sliding velocity (0.5m/s, 1.0 m/s and 1.5 m/s). For discs (MC 12 and MC 13) the wear rate decreased linearly with increasing sliding velocity, since the pins on Cast Iron Grey centrifuged, the wear rate decreased to 1.0 m / s, and 1, 5 m / s the wear rate increased slightly, as determined by the instability caused by surface heating and the formation of the oxide layer. The pair centrifuged / MC 13 performed better than 0.5 m / s and centrifuged pair / MC 12 to 1.0 and 1.5 m / s. It was found that the prevalent wear mechanisms are adhesion (0.5 m / s), adhesion + oxidation (1.0 m / s) and oxidation (1.5 m / s). In all sliding velocities, the main mechanisms of wear are followed by abrasion