Thesis (Ph.D.) -- McMaster University, 1998. / Includes bibliographical references (p. 295-305). Also available via World Wide Web.

Thesis (Ph. D.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 181-192).

Thesis (Ph. D.)--University of North Texas, Dec., 2008. / Title from title page display. Includes bibliographical references.

Thesis (Ph.D)--Mechanical Engineering, Georgia Institute of Technology, 2010. / Committee Chair: Streator, Jeffrey; Committee Member: Blanchet, Thierry; Committee Member: Cowan, Richard; Committee Member: Danyluk, Steven; Committee Member: Neu, Richard; Committee Member: Thadhani, Naresh. Part of the SMARTech Electronic Thesis and Dissertation Collection.

The present thesis focuses on characterisation of microstructure and the resulting mechanical and tribological properties of CVD and PVD coatings used in metal cutting applications. These thin and hard coatings are designed to improve the tribological performance of cutting tools which in metal cutting operations may result in improved cutting performance, lower energy consumption, lower production costs and lower impact on the environment.  In order to increase the understanding of the tribological behaviour of the coating systems a number of friction and wear tests have been performed and evaluated by post-test microscopy and surface analysis. Much of the work has focused on coating cohesive and adhesive strength, surface fatigue resistance, abrasive wear resistance and friction and wear behaviour under sliding contact and metal cutting conditions. The results show that the CVD deposition of accurate crystallographic phases, e.g. α-Al2O3 rather than κ-Al2O3, textures and multilayer structures can increase the wear resistance of Al2O3. However, the characteristics of the interfaces, e.g. topography as well as interfacial porosity, have a strong impact on coating adhesion and consequently on the resulting properties.  Through the deposition of well designed bonding and template layer structures the above problems may be eliminated. Also, the presence of macro-particles in PVD coatings may have a significant impact on the interfacial adhesive strength, increasing the tendency to coating spalling and lowering the surface fatigue resistance, as well as increasing the friction in sliding contacts. Finally, the CVD-Al2O3 coating topography influences the contact conditions in sliding as well as in metal cutting. In summary, the work illuminates the importance of understanding the relationships between deposition process parameters, composition and microstructure, resulting properties and tribological performance of CVD and PVD coatings and how this knowledge can be used to develop the coating materials of tomorrow.

Made available in DSpace on 2014-06-11T19:28:34Z (GMT). No. of bitstreams: 0 Previous issue date: 2006-01-20Bitstream added on 2014-06-13T20:58:34Z : No. of bitstreams: 1 cornelio_gt_me_guara.pdf: 7494292 bytes, checksum: 4665b80734a19910838d0896e5face70 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / O avanço da tecnologia de laminação incrementou as solicitações sobre os cilindros laminadores, e, portanto, o desenvolvimento de materiais mais resistentes ao desgaste, visando aumento da produtividade do laminador e melhor qualidade superficial dos produtos laminado, em especial tiras a quente. Como estudo de desgaste em campo é muito complexa devido à influência de diversos mecanismos e muitas vezes combinados entre si, os ensaios laboratoriais têm se mostrado como um meio mais fácil para estudar os materiais em serviço, além de auxiliar o projeto novas ligas. Dessa forma, foi proposto um ensaio de desgaste abrasivo puro para um tribômetro Plint & Partners, modelo TE-079, com o intuito de simular condições de utilização das últimas cadeira do trem acabador de um laminador de tiras a quente. Para sua validação foram utilizados três materiais: o ferro fundido de coquilhamento indefinido, o ferro fundido branco de alto cromo e o ferro fundido branco multicomponente, os quais apresentam comportamento conhecido em serviço. Esses materiais foram submetidos a uma caracterização metalográfica, microdureza e topografia de desgaste. Os resultado obtido mostraram-se coerentes com a prática observada na aplicação real, ou seja, reproduziram o comportamento de desgaste no laminador, sendo válida a proposta do ensaio tribológico. / The progress towards mill technology has increased the demand on the rolling mill rolls, and therefore, the development of wear resistant seekink productivity of the rolling mills and better superficial quality of the rolled products, especially in the hot strip mill has also increased. As the wear study in field is very complex due to the influence of several mechanisms wish are usually combined amongst themselves, the labs test have shown an easy way to study the materials in service, besides aiding the project of new leagues. In that way, a pure abrasive wear test was developed tribômetro Plint & Partners, model TE-079 with the intent of simulating the job conditions in the hot strip mill finishing chairs. For the validation three materials were used: an indefinite chill cast iron, a high chrome cast iron and a kind of multicomponent white cast iron, which presents knowm behavior in service. Those materials were submitted to a metallography characterization, microhardness measurement and wear topograpy observation. The obtained results were shown coherent with the practice observed in the real application, and then became possible a prediction of that behavior for the materials projects developed at laboratory, being valid the proposal of the rehearsal tribológico.

Low friction lubricant development provides a worthwhile contribution to vehicle CO₂ emission reduction. Conventional low friction lubricant development focuses on empirical processes using out dated engine technology and old test methods. This strategy is inefficient and restricts the lubricant's potential. A new method proposed in the present research combines tribological simulations with rig, engine and vehicle tests. This approach provides insights undocumented until now. The contribution to CO₂ emission reduction from individual engine components on vehicle drive cycles that include warm-up is predicted using lubricants down to the new SAE 8 viscosity grade. A bearing model is used to design the lubricant's non Newtonian characteristics to achieve friction reduction. An isoviscous lubricant with a viscosity of 4.6 cSt is shown to achieve the minimum friction in the bearing. The research shows that by starting with lubricants having kinematic viscosities higher than this value, it is possible to improve lubricant performance by lowering viscosity index (VI), introducing shear thinning, or reducing the density and pressure viscosity coefficient. Conversely, for lubricants with lower starting viscosities it is shown that higher VI values, more shear-stable lubricants and higher densities and pressure viscosity coefficients are required. The model predicts that high oil film pressures occur in the bearing and cause significant local lubricant viscosity increase (300%), indicating that the lubricant's pressure viscosity behaviour is important here, despite the contact being conformal. Simulation and motored engine testing establishes lubricant behaviour in the piston-to-bore conjunction. This analysis identifies a poor correlation between measured and predicted values at low engine speeds. A rig-on-liner tribometer shows that this error is attributable to a deficiency in the simulation's characterisation of boundary regime friction. An oil pump test determines how a modern variable displacement oil pump (and its control system) responds to lowering viscosity. The hypothesis that low viscosity lubricants cause the parasitic load from this component to increase is disproven using this component-level rig test. Chassis dynamometer testing compares the CO₂ reduction performance of lubricant thermal management systems to the values achieved by reducing the viscosity grade. CO₂ reductions of between 0.4% and 1.0% are identified using a cold-start new European drive cycle (NEDC) with a 5W-30 preheated to 60°C and 90°C respectively. Reductions in CO₂ emissions between 0.4% and 1.2% are found on the NEDC by lowering the oil fill volume from 5.1 L to 2.1 L. For the unmodified case, a 3.7% reduction in CO₂ emissions is reported by reducing the viscosity grade from a 5W 30 to an SAE 8 in the NEDC. The performance of a novel external oil reservoir is simulated to understand its ability to retain oil temperature during the vehicle cool-down procedure. An oil temperature of 65°C at the end of the soak period (following a prior test where the oil was assumed to reach 90°C) is predicted by installing insulation to the reservoir and indicates that a viable method to achieve the CO₂ benefits identified through lubricant preheating tests exists. A full vehicle model combines the outputs from each of these sub-models to predict lubricant performance on the NEDC the new World-wide harmonized light duty test cycle (WLTC). This new approach provides a tool that enables next generation low friction lubricants to be developed. The model predicts that an SAE 8 lubricant can reduce CO2 emissions by 2.8% on the NEDC and 1.9% on the WLTC compared to a 5W-30. A theoretical experiment, where all lubricant related friction was deleted from the simulation, predicts that lubricant-related CO₂ emissions are 8.7% on the NEDC and reduce to 6.3% on the WLTC. These results indicate that the planned adoption of the WLTC in September 2017 reduces the potential contribution to CO₂ emission reduction from lubricants by 28%.

The losses in an internal combustion engine are dominated by thermal and parasitic sources. The latter arises from mechanical inefficiencies inherent within the system, particularly friction in load bearing conjunctions such as the piston assembly. During idle and at low engine speeds, frictional losses are the major contributor to the overall engine losses as opposed to the dominant contribution of thermal losses under other driving conditions. Given the relatively small size and simple structure of the top compression ring, it has a disproportionate contribution to the total frictional losses. This suggests further analysis would be required to understand the underlying causes of compression ring behaviour throughout the engine cycle. The available literature on tribological analyses of compression rings does not account for the transient ring elastodynamics. They usually assume a rigid ring for film thickness and power loss predictions, which is not representative of the ring's dynamic response. A combined study of ring elastodynamic behaviour and its tribological conjunction is a comprehensive approach.

Contact between rough surfaces occurs in numerous engineering systems and in many instances influences the macro behavior of the system. In many instances, the interaction between rough surfaces, affect the macro behavior of the system. Effective treatment of systems containing rough surface contact requires multiscale modeling and analysis approach. It is the goal of this research to develop simple methods for treating contact of rough surfaces so as to facilitate multiscale analysis of systems containing rough surface contact and friction. This dissertation considers a multi-scale approach that includes interaction at nano-scale, micron-scale and accounting for their cumulative effect as to what we normally perceive to be the influence of contact surfaces and friction. In linking each scale to a higher scale this study employs statistical means to obtain cumulative effect of smaller-scale features. A mixed interactive/optimization technique is used to derive, in approximate closed form, equations for the contact load and real area of contact dependence on approach and parameters of rough surfaces. The equations so derived relate the normal and tangential components of contact load to displacement and surface parameters for three types of contact. The nature of contact interaction that include elastic, elastic-plastic, visco-elastic, and visco-elasto-adhesive behavior are considered and equations relating the normal and tangential contact load to approach and relative sliding are obtained in approximate closed form. The approximate equations provide a tool for efficient calculation of contact force components, especially in surface optimization efforts where repetitive calculation of contact force components may be needed. The approximate equations also facilitate a multi-scale dynamic analysis wherein the effect of contact interaction can be readily included in a mechanical system model. Several dynamical problems involving mechanical systems with friction contact are presented and nonlinear dynamic analyses are employed to link the micron-scale properties of surface to the macro-scale properties of the mechanical system. These lead to, perhaps, the first derivation of contact frequency and damping in rough surface contact.

Graphene is a single atomic sheet of graphite that exhibits a diverse range of unique properties. The electrons in intrinsic graphene behave like relativistic Dirac fermions; graphene has a record high Young's modulus but extremely low bending rigidity; and suspended graphene exhibits very high thermal conductivity. These properties are made more intriguing because with a thickness of only a single atomic layer, graphene is both especially affected by its environment and readily manipulated. In this dissertation the interaction between graphene and its environment as well as the exciting new physics realized by manipulating graphene's lattice are investigated. Lattice manipulations in the form of strain cause alterations in graphene's electrical dispersion mathematically analogous to the vector potential associated with a magnetic field. We complete the standard description of the strain-induced vector potential by explicitly including the lattice deformations and find new, leading order terms. Additionally, a strain engineered device with large, localized, plasmonically enhanced pseudomagnetic fields is proposed to couple light to pseudomagnetic fields. Accurate strain engineering requires a complete understanding of the interactions between a two dimensional material and its environment, particularly the adhesion and friction between graphene and its supporting substrate. We measure the load dependent sliding friction between mono-, bi-, and trilayer graphene and the commonly used silicon dioxide substrate by analyzing Raman spectra of circular, graphene sealed microchambers under variable external pressure. We find that the sliding friction for trilayer graphene behaves normally, scaling with the applied load, whereas the friction for monolayer and bilayer graphene is anomalous, scaling with the inverse of the strain in the graphene. Both strain and graphene's environment are expected to affect the quadratically dispersed out of plane acoustic phonon. Although this phonon is believed to provide the majority of graphene's very high thermal conductivity, its contributions have never been isolated. By measuring strain and pressure dependent thermal conductivity, we gain insight into the mechanism of graphene's thermal transport.