With the possession of extremely broad unique properties, particulate reinforced aluminum composites are very attractive in diverse applications. Aluminum matrix particulate composites are challenging to work with. A single pressing and sintering process was used to fabricate the reinforced aluminum composites in this study. The key advantage of this method is its comparative low expense. However, abrasive reinforcement powders can lead to shorter tool life. To study the fundamental wear mechanisms during the die compaction process, a new method was developed and combined with experiments to quantify tool wear. Automatic die compaction experiments and tribological experiments are employed in this study. The tribologcial experiments consist of a modified pin-onlat test and a modified loop test. Mass loss of tools was recorded during all the experiments. A new tool wear model was used in this study to investigate effect of different hard phase and different lubricant level on die compaction process.

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Under current regulations, gasoline engines are facing lubricity and wear challenges that need to be met by enhanced gasoline lubricity. Gasoline lubricity can be enhanced by lubricity improvers such as heavy fatty acid methyl esters. This thesis presents the ‘High Frequency Reciprocating Rig’ (HFRR) tests carried out on a standardized tribological test rig as per a modified version of ASTM D6079, to account for the effects of volatility of gasoline. Testing 5 gasoline types (gasolines A-E) blended with 2 lubricity improver types (LI1-2) at 2 concentrations, 250 and 500 ppm, provided insights on the changes in lubrication behavior with different gasoline composition, LI type, and concentration. The gasoline types with higher aromatic content and average carbon number (lower volatility) resulted in less wear and better lubricity regardless of LI concentration. The highly aromatic gasoline “A” performed better with the fatty acid-based LI1. Gasolines “B-E”, which are less aromatic, resulted in less wear with the ester-based LI2. The decrease in wear volumes with LI2 was more pronounced with the highly volatile gasolines B and E. These insights were mainly challenged by the failure of some tests due to the high volatility of gasoline. To mitigate this effect and confirm the findings, less volatile gasoline surrogates were designed to mimic the composition of the gasoline types on functional group basis, and were blended with the same lubricity improvers, and then tested using the same method. This improved the results and showed that high aromaticity enhanced the lubricity of the gasoline blends, especially with fatty-acid based LI1, but degraded it beyond 50% aromatic content. The enhancement of lubricity with higher average carbon number was also highlighted. To create deeper understanding of the lubrication mechanisms involved, it is recommended to study the rheological properties of the blends, analyze the chemical composition of the deposits on the wear tracks, and repeat the tests with continuous supply of lubricant to further decrease the effect of gasoline volatility

Tribology is the science of interacting surfaces in relative motion. It is specifically concerned with the friction, wear and lubrication of these surfaces. Although tribology has conventionally been associated with the surface interaction of mechanical systems, concepts of tribology have also been important in the study of biological systems. Biotribology is one of the newest fields to emerge in the discipline of tribology. It can be described as the study of friction, wear and lubrication of biological systems, mainly synovial joints such as the human hip and knee. Osteoarthritis (OA) is partially characterized by the loss of articular cartilage from the contacting surface of the articulating bones in synovial joints. Although it has been studied extensively, the exact pathways and pathogenesis of OA have yet to be determined. Several factors have been cited as possible contributors to the condition. These factors can primarily be grouped into two categories of mechanical or biochemical abnormalities. Research in biotribology enables the examination of both the mechanical and biochemical factors involved in joint lubrication and OA. This research has focussed on the mechanisms of normal joint lubrication, as well as the possible connections between biotribology and osteoarthritis. Particular emphasis is placed on the effects of biochemical changes and environment on cartilage wear and damage. Studies were carried out using a test device developed to study the tribological properties of articular cartilage, in vitro. A cartilage-on-cartilage test configuration was used with bovine articular cartilage and a cartilage-on-stainless steel configuration used with lapine articular cartilage. Articulating surfaces were put in sliding contact under a normal load. Natural and biochemically modified environments were created to simulate possible normal and pathologic in vivo conditions. Wear and friction of the articular cartilage were measured and related to biochemical environments which are suspected in clinical cases of OA. Quantitative measurement of cartilage wear was achieved through hydroxyproline assay of the post-test lubricants. Surface and subsurface damage were also examined through the use of scanning electron microscopy and histological staining techniques. The results of four separate studies demonstrated that: (1) exposure of bovine cartilage to collagenase-3, an enzyme suspected in the cartilage degeneration seen in OA, significantly increased cartilage wear (p = 0.001); (2) lapine cartilage with surgically induced OA exhibited higher coefficients of friction, but no significant increase in wear over normal cartilage from the same animal; (3) the addition of white blood cell lysate, comparable to what would be seen in mild joint inflammation, to synovial fluid significantly increased cartilage wear over normal synovial fluid (p = 0.002); (4) the removal of "boundary lubricating" surface-active phospholipids (SAPLs) from normal synovial fluid had no significant effect on cartilage wear. These results demonstrate that biochemical changes in the cartilage, as well as the synovial fluid, can lead to increased wear of and damage to the articular cartilage surface. How these changes may occur in living systems remains to be determined. The use of the tribological test device developed and various analytical techniques has made it possible to quantitatively evaluate the effects of biochemical changes and environment on the wear and damage of articular cartilage. These studies have demonstrated that research in biotribology has the potential to make significant contributions to the current knowledge not only of normal joint lubrication but of joint pathology as well. / Ph. D.

Novel coatings have been designed to solve problems associated with biofouling of marine structures, particularly ship hulls. The best candidates to date are multilayered coatings incorporating silicone rubber technology. These materials are efficient because they exhibit excellent release properties. However, they are very soft and tend to be more susceptible to various forms of mechanical damage. Fundamental analysis of the durability of these coatings has been done using standard laboratory tests. Simulative studies are essential to screen candidates as well as to predict the true life of the systems. The goal of this project was to develop a testing protocol for the evaluation of the durability of elastomeric easy release coatings and to implement it on selected candidate coatings. A brushing apparatus was designed and built to simulate the cleaning processes of ship hulls. Wear was measured with profilometry. The proposed methodology is valuable to study the processes of wear of the coatings, to screen various materials and to identify parameters, either functional or material, which would directly affect their durability. Two groups of candidate coatings were tested: the EXS series and the NRL series. The EXS samples showed better wear resistance than the NRL samples and showed no dependence on the rotational speed of the brushes. The NRL samples showed that increasing the sliding speed resulted in a decrease in wear. An increase in the applied load resulted in increased wear for both sample series. The effect of coating thickness was also investigated and discrimination between the proposed coatings could not be established because the tips of the bristles were sharp and irregular. Scratches matching the path of the brush bristles were observed in the wear scars of both sample types under all load and speed conditions. The NRL samples also exhibited ridges perpendicular to the sliding direction similar to the abrasion pattern. / Ph. D.

Polymers were slid on rough hard steel surfaces with normal loads which caused full penetration (real and apparent areas equal) and partial penetration (real less than apparent area). Wear data for polyvinylchloride (PVC) and polychlorotrifluoroethylene (PCTFE) was obtained on a pin-on-disk machine using neutron activation analysis A (NAA). Observations of the wear process were made in the scanning electron microscope (SEM) both before, during, and after the wear experiment. It was observed that these polymers along with Nylon 6-6 tend to wear in discrete sites rather than continuous films. At these discrete sites the polymer shears at an angle which is dependent on the mechanical properties of the polymer and on the asperity angle. There appears to be a minimum shear angle beyond which no wear occurs. / Ph. D.