This thesis work is an evaluation of journal bearings in manual transmissions in automobiles. Today both journal- and needle bearings can be positioned into the gearboxes and in order to reduce the power loss developed by friction when a relative angular velocity arises, the right type of bearing must be chosen. In order to succeed, this work is aimed to develop a Matlab simulation model, which should be used as a tool in the design process of manual transmissions. The program development is later supposed to be followed by real tests of journal bearings, partly to cover things that can not be covered in the model but also to confirm how well the model reflects the reality. The absence of resources resulted in no performed real test and therefore was a comparison between theoretical-  and practical results not possible. Here the plain journal bearings in full film lubrication will have an disadvantage compared to the needle bearings regarding the power lost. To reduce the drag below the values of the needle bearings a modified journal bearing in the area of boundary lubrication with a very low coefficient of friction may be an option. But problems with wear under this condition could most certainly be devastating and must be further investigated with real tests. Out of a efficiency point of view the most suitable bearing position is the gear in the most frequently used area. Here it is assumed to be the 4th gear. A suitable journal bearing design should have a small sliding surface area in order to minimize the viscous drag. To achieve low friction the boundary lubricated area could be a good idea in cases when wear is not a critical factor. To longer the useful life nitrocarburizing is recommended, which both reduces wear and lower the coefficient of friction, in cases of asperites in contact. In order to work under the full film lubricated condition, with neglected wear, the sliding area needs to be large enough to create the required oil pressure.

This thesis work sought to find a tribological testing method suitable for cementedcarbide drill bit inserts used when drilling rock. A review of the literature publishedon the matter showed that there are quite a few test methods developed for wearstudies with cemented carbides, but most of them were not designed for the rockdrilling industry. Published studies performed with the found methods and articleswith analyzed field tests have been studied. It is generally agreed upon that the stepsof wear is that the binder disappears first, followed by removal of carbide grains. Themechanisms of binder phase and carbide grain removal is somewhat debated, butalmost every study observes fracture of the carbide grains. The wear test created inthis thesis was shown to give wear linear with time, but not with load. The newmethod was shown to be capable of distinguishing between different cementedcarbides worn in three body abrasion against different rocks. Analysis of the wornsamples shows that there are similarities with bit inserts worn in field testing. Many ofthe observations made during the analysis are also similar to observations inliterature.

This thesis work is performed at Sandvik Mining Rock Tools, a world leading supplier of rock drilling tools. The work is part of developing a new tribological wear test method for cemented carbide drill bit inserts. The test method has earlier been judged successful in mimicking the rotary-percussive rock drilling process because it gives the same wear mechanisms as have been observed for inserts used in rock drilling. During testing the cemented carbide drill bit insert is pressed against a moving rock surface while water and particles are added to the contact area. The particles are present to simulate the rock crushings formed during drilling. They are believed to cause abrasive wear of the inserts. In this work the effect of load, particle material and particle size are studied. When adding silica particles, which are softer than the cemented carbide material, no correlation is obtained between wear rate and load or particle size. Cracking of WC grains, added rock material and removal of pieces of carbide material are seen at the worn sample surfaces. These observations are similar to observations described in other works about wear of cemented carbide. Adding alumina particles, which are harder than the sample material, gives high wear rate and ground/striped sample surfaces. The wear rate increases with alumina particle size.

This study considered using a relatively new method to study soil-tool wear which could drastically reduce the time and associated costs of traditional wear studies. The goal was to utilize discrete element method (DEM) simulations to recreate the results of a circular soil bin test in order to develop a relationship that could be used to predict wear under different conditions. Through the application of DEM, simulations could be used to study different materials or designs intended to result in improved wear performance.<p> Three replications of aluminum cylindrical bars were worn during 400 km of travel in a circular soil bin. Wear was quantified by measuring the change in radius of the cylinders at 18-degree intervals around their circumference. Mass data were also obtained to provide an overall average of wear occurring on the bar and to validate the radii measurements.<p> The DEM simulations were executed using EDEM software. Conditions present in the physical soil bin trials were simulated by recreating components in the soil bin and incorporating soil properties that were directly measured, using representative soil samples. Forces exerted on the bar by the soil and the relative velocities between the soil and tool were used to generate a relationship to predict wear of the bar. The wear equation was verified using a portion of the experimental data from the soil bin.<p> The wear model showed promise in predicting the amount of wear recorded in the soil bin through the application of DEM-predicted compressive forces and relative velocities between the tool and soil particles. The Archard equation for wear was modified to create a non-linear equation. Plotting the measured wear against the wear predicted from the fitted equation produced a trendline with a slope of 0.65. Although a perfect correlation would have produced a slope of 1, the model was able to predict a large portion of the wear that occurred. Refinement of the model could further be achieved with changes in the design of the geometry used in the simulation and through verification of force predictions with experimental data. Because of the variable nature of wear, additional replications of tools in the soil bin would have increased the number of data points available to create the model and reduced the impact of outlying data. With these recommended improvements, the wear model has the ability to very accurately predict the wear of a cylindrical bar.

<p>Human joints are able to withstand millions of loading cycles with loads regularly more than 3 times an individual's body weight in large part due to the unique bearing properties of articular cartilage, a strong, slippery tissue that covers the ends of long bones. PRG4 is a boundary lubricating glycoprotein present on the cartilage surface and in the synovial fluid surrounding it. While evidence that PRG4 lubricates and preserves normal joint function is strong, little is known of its effect on cartilage surface properties, the mechanism by which it lubricates, or its postulated role of preventing wear on joints. The effect of PRG4 on cartilage friction, wear, structure, morphology, and the mechanisms by which it mediates these factors are studied here. Methods to study these parameters at the microscale using atomic force microscopy are also developed. </p><p>Cartilage of mice with the Prg4 gene (which expresses PRG4) deleted is shown to be different in a number of ways from wild type cartilage. The uppermost layer is thicker and less uniform and the surface is rougher and softer. There is also a loss of proteoglycans, structural components of cartilage, from the underlying superficial tissue, and apparent tissue damage in some cases. Wear in the presence of PRG4 in shown to be significantly lower than in its absence, a finding which may have direct implications for prevention and treatment of osteoarthritis. It appears that PRG4 needs to be present in solution, not merely on the cartilage surface to have this effect, indicating that adsorption properties are important for wear prevention.</p> / Dissertation

This research studies individual and combined effects of hydrogen gas exposure and low temperature on the tribological characteristics of Ti-6Al-4V. Experimental approaches include test system modification and tribological analysis. An existing ballon- disk tribometer was modified to allow liquid nitrogen to be constantly injected into an insulated test chamber to enable testing at low temperature. Twelve 3.8 cm diameter Ti-6Al-4V disks were manufactured and polished, then half were exposed to pure hydrogen gas at elevated temperature and pressure and the remaining disks were untreated. The testing was split in to four groups of three disks based on testing temperature and previous hydrogen exposure. A silicon nitride ball was used for all tests. Each group was tested at two normal loads, 10N and 20N, at the same linear speed. Group 1 was unexposed and tested at room temperature, Group 2 was unexposed and tested at low temperature, Group 3 was exposed and tested at room temperature and Group 4 was exposed and tested at low temperature. Average friction coefficients and the specific wear rate were calculated from the test data. Also high-resolution digital microscope imaging was used to observe and characterize the wear mechanisms of the four groups of samples. Results show that hydrogen exposure facilitated adhesive wear of the surface and that low temperature induced a slip-stick wear mechanism under higher loads, but not at lower loads and regardless of exposure to hydrogen gas. This research opens avenues for future investigation in effects of hydrogen and low temperature embrittlement on the tribological performance of materials. With the increasing interests in hydrogen energy, the present work established a foundation for future study.

This thesis research synthesizes a new class of composite materials and investigates their properties, performance, and potential applications. The new materials that are multi-phase and multifunctional are considered for use in car cooling systems, internal combustion engine waste-heat-power generators, and engine crack healing which are major problems plaguing the auto industry. This research uses primarily experimental approaches to study the magnetocaloric compound, Ge5Si2Ge2 (GSG), that has large strain effects. Such a material was formed into a composite using Al as a substrate. The newly developed composite, GSG-Al, is the first material of its kind that possesses self-healing effects in cracks. X-ray diffraction was used to determine the crystal structures that existed within the material. It is found that the sintering process used to create the composite caused the formation of GdAlGe that is a magnetic compound with a high Curie temperature. The GSG-Al has a wide variety of crystal structures, ranging from face centered cubic for aluminum phases to monoclinic and orthorhombic phases for GSG. The discovery of GdAlGe confirmed that alpha-ThSi-type tetragonal and YAlGe-type orthorhombic crystal structures existed. Transmission electron microscopy (TEM) was used to analyze the wear debris collected during tribo-testing. The debris were also analyzed using energy-dispersive X-ray spectroscopy (EDS) for chemical analysis. The GSG-Al was put through tribological studies at several different temperatures to determine the thermal effects on the composite. The GSG-Al, although found to be ductile, showed high resistance to wear when compared to a common aluminum alloy, Al 6061-T651. The wear rate decreased with increasing temperature when the temperature was increased from the room temperature to 150 degrees C. Results showed that with GSG, the composite did not show cracking common in Al alloys. This was due to the unique thermal expansion properties of the GSG-Al. The phase transformation induced a significant volume expansion in the material and thus a giant strain effect. This research opens new approaches in energy conversion and improving efficiency of automobile engines. The composite developed here is important for future scientific investigation in the area of multifunctional materials as well as materials that exhibit self-healing tendencies.

Polyetheretherketone (PEEK) is a designation given to materials of the polyaryletherketone family having a characteristic distribution of ether and ketone groups in the polymer backbone. PEEK materials have high strength and chemical resistance as well as very high melting points and glass transition temperatures. Because of this combination of properties, PEEK materials find use for wear application in extreme environments where they provide a light-weight and corrosion resistant bearing material that often does not require lubrication. An initial study focused on determining the effects of supplier and molecular weight on the wear of particular PEEK materials, in addition to the effect of contact pressure. This work is significant because it highlights the fact that tribologically relevant polymers, such as PEEK materials, vary greatly in terms of their polymer morphology and processing history, and this variation must be recognized by investigators when reporting wear data. Because of their light weight, chemical resistance, and self-lubricating properties, polymers are used in applications ranging from biomedical to aerospace. Some polymers exhibit significant differences in wear resistance based on whether they are in unidirectional or multidirectional sliding. Shear induced polymer chain orientation is believed to be responsible for this behavior. Polyetheretherketone (PEEK) has excellent wear resistance, but its multidirectional sliding behavior has not been thoroughly investigated. A factorial multidirectional pin-on-plate wear study of PEEK was conducted with a focus on molecular weight and sliding path directionality. These factors were studied for their correlation to overall wear performance. Additionally, transfer film thickness was measured at locations along the wear path using white light interferometry. A result of this work has been a greater understanding of PEEK wear mechanisms in various sliding configurations and how they relate to transfer film formation. A major outcome was the development of a quantitative metric to describe transfer film thickness and continuity. It was found that thinner more continuous transfer films form under sliding conditions that change direction rather than overlapping along the same path. The thinner more continuous transfer film was found to also correspond with statistically lower wear behavior. Scanning electron microscope (SEM) investigation of the transfer film and pin wear surface confirmed the relationship between transfer film quality and wear.

The effects of abrasive particle size and tool surface roughness on tool and work wears of a polishing process were investigated. It was aimed to obtain a polishing condition that could result in a high work wear while the tool wear was low. An analytical study was first done to examine how the various operating conditions affected the wear rates of tool and work. It was done from a wear model developed by Su and Horng [1]. This model was further extended in the study to allow the wear rate analysis for an abrasive particle with ellipsoid shape. It was shown that an enhancement of abrasive particle size or tool surface roughness would increase the work wear while decrease the tool wear. Several sets of experiments were conducted to confirm the predictions of analytical study. It was shown that the experimental trends were the same as the analytical ones. Finally, the possible causes of observed phenomena and the limitations of the study were discussed.

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