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<p>In this work, we tested the ability of an experimental system, involving the use of micropipettes as force transducers, to measure the coefficients of friction of several systems. Using a magnetic pipette puller, the micropipettes were produced by first heating and stretching the glass. The pipettes are then manipulated into an L-shape. This geometry allows one arm to act as the normal force transducer, and the other to act as the lateral force transducer for the purposes of friction measurements. We then analyzed the variation of the friction force of 15 micrometre polystyrene beads in contact with silicon and polystyrene in a fluid environment at increasing velocities. We also measured the variation in friction coefficient of poly(dimethyl siloxane) coated polystyrene beads in contact with a silicon surface. Our results were then compared to known values where possible, and the variation of the friction coefficient with increasing velocity was fit to a known phenomenological model. From our experiments, we have shown that our experimental technique can provide reproducible friction coefficient measurements, and these coefficients vary with velocity in a known manner. These results confirm the ability of micropipettes to act as both normal and lateral force transducers in friction experiments, and that they have the potential to be used in measuring friction coefficients of more complex materials.</p> / Master of Science (MSc)

<p>The aim of this study was to explore environmentally friendly solutions to reduce the friction present in automotive transmissions.</p> <p>A 2005 Ford Escape Hybrid transmission was used in this study to establish reasonable operating conditions for the gear surfaces.</p> <p>Background on gear operation and surface interaction was studied to understand the nature of the contact between the gear surfaces. Based on this, a mathematical model of gear interaction was developed and used to bracket the loading conditions of the gear tooth interface to be up to 1.5GPa of contact pressure with 2m/s relative sliding velocity. This information was used to aid in the identification of suitable surface engineering technologies and set the operating conditions for reciprocating tribometer based measurements.</p> <p>Additionally, tribological tests were performed on pin-on-disc samples which were treated with various surface treatments. The resulting wear surfaces were then studied using optical and Scanning Electron Microscopy (SEM) as well as Raman Spectroscopy. These techniques were used to better understand the mechanisms associated with wear and the role that the surface treatments played in reducing wear. Based on the testing performed, the best surface treatment for this application was a super finishing process. This process also met cost and environmental constraints. An in-house dynamometer was also developed to be used in the future full scale testing of a transmission.</p> / Master of Applied Science (MASc)

Friction in machining is a complex phenomenon that can directly affect cutting productivity and product quality. Currently, different coatings are developed for machining applications which can increase tool life in the machining processes. Since performing a real machining test to quantify the friction is expensive and time-consuming, developing a bench scale testing method to simulate the friction in machining can reduce the cost and help researchers and industries select a suitable coating for their specific applications. The goal of this work was to study the adhesion between the tool and workpiece material under machining conditions by simulating them using a heavy-load high-temperature tribometer. A high normal load was applied to plastically deform the workpiece material. The contact zone was then heated up using a resistance heating method. The normal load should be in the range that can generate a plastic flow on the surface of the workpiece material prior to seizure. Three groups of in-house coatings were tested to study the effects of coating deposition parameters on the coefficient of friction. The results of these tests showed that the coating with the lowest bias voltage and highest Nitrogen pressure had the best tribological performance. As a next step, three different commercial coatings were selected. Super duplex stainless steel was chosen as the workpiece material and the tribometer tests were performed. To validate the tribometer results real machining tests and tool wear analysis were performed. AlTiNOS+ WC/C was observed to be a lubricious coating which reduced the cutting force and coefficient of friction during the running-in stage. However, the low hardness of the coating provided little abrasion resistance and was removed after the first pass. AlTiNOS+ TiB2 demonstrated a good combination of hardness and lubricity associated with improved coating tribological performance as well as wear resistance. / Thesis / Master of Applied Science (MASc)

MACHINABILITY ENHANCEMENT OF STAINLESS STEELS THROUGH CONTROL OF BUILT-UP EDGE FORMATION / Demand for parts made from stainless steel is rapidly increasing, especially in the oil and gas industries. Stainless steel provides a number of key advantages, such as high tensile strength, toughness, and excellent corrosion resistance. However, stainless steel cutting faces some serious difficulties. At low cutting speeds, workpiece material and the chips formed during machining tend to adhere to the cutting tool surface, forming a built-up edge (BUE). The BUE is an extremely deformed piece of material which intermittently sticks to the tool at the tool-chip interface throughout the cutting test, affecting tool life and surface integrity. Unstable BUE can cause tool failure and deterioration of the workpiece. However, stable BUE formation can protect the cutting tool from further wear, improving the productivity of stainless steel machining. This thesis presents an in-depth study of machining performance using different coated tools and various coolant conditions to examine the nature of the different tool wear mechanisms present during the turning of stainless steels. Then, different textures are generated on the tool rake face to control the stability of BUE and reduce friction during the machining process. Results show that the BUE can significantly improve the frictional conditions and workpiece surface integrity at low cutting speeds. Finally, square textures on tool rake face were found to control the stability of BUE and minimize the friction at the tool-chip interface. This reduces the average coefficient of friction by 20-24% and flank wear by 41-78% and increases surface finish by 54-68% in comparison to an untextured tool. / Thesis / Doctor of Philosophy (PhD) / Three main objectives are presented in this thesis. The first is a detailed investigation of the performance of stainless steel machining obtained by the use of different coated cutting tools and various cooling conditions. The goal of this research is to assess the reduction of tool service life, productivity, and part quality. The thesis also examines the causes of workpiece material adhesion to the cutting tool during the cutting test and to better explain its effects on tool wear and workpiece surface finish. This phenomenon is known as the "built-up edge" (BUE). Finally, different textures are applied on the cutting tool via a laser to stabilize the BUE formation on the cutting tool, thereby improving the quality of the part.

Additive friction stir deposition (AFSD) is an emerging solid-state additive manufacturing process that leverages the friction stir principle to deposit porosity-free material. The unique flow of material that allows for the transformation of bar stock into a near-net shape part is driven by the non-linear heat generation mechanisms of plastic deformation and sliding frictional heat generation. The magnitude of these mechanisms, and hence the total applied thermal power, implicitly depend on the thermal state of the system, forcing power input to become a dependent variable. This is not the case in other 3D printing methods; thermal power can be controlled independently. In this work, the heat generation in AFSD is explored, and its transfer is quantified. In particular, the time-dependent ratio between the amount of conduction into the AFSD tool versus into the substrate is quantified. It was found for the conditions tested with a single-piece AFSD tool, conduction up the tool was on the order of the conduction into the stir. For a more modern three-piece tool, the ratio between the tool and the substrate varied between 0.3-0.1. It was also found that traversing faster resulted in more heat flux into the substrate as would be expected by moving heat source modeling. The total heat generated was also quantified as being equal to between 60% and 80% of the mechanical spindle power depending on the tool type and the exact process conditions. That ratio was found to be time-invariant. At the same time, this changing heat flux ratio was shown to dramatically alter thermocouple measurements in the tool, showing the uncertainty of that method of process control. The contact state between the stir and the tool was treated as a thin conductive layer and a contact heat transfer coefficient was calculated on the order of 20 frac{kW}{m^2K}. The limitations of this treatment were found to occur when a significant amount of the heat generation came from frictional heating rather than plastic deformation. This implies that any measurement conducted in the tool is related to the stir by a complex function driven by the state of the stir; showcasing the need for more well-understood in-situ monitoring. Finally, some of the ideas about thermal control are applied to a case study on the repair of corroded through holes using AFSD to restore fatigue life. It was found that modifying the thermal boundary conditions and applying active cooling at the end of the repair could improve the fatigue life drastically. This was due to less time spent in a thermally active region leading to less heterogeneous nucleation and less grain boundary nucleation. This more preferred microstructure morphology led to a change in the fracture mode and increased the number of cycles to crack initiation and the number of cycles after crack initiation. / Doctor of Philosophy / Metal 3D printing of industrially relevant aluminum alloys is plagued with problems. Additive friction stir deposition seems well posed to overcome some of the problems associated with aluminum printing. Being able to 3D print these alloys with properties that are as good as traditional manufacturing offers a large potential cost and time savings over traditional manufacturing for the aerospace industry (e.g. Boeing, Lockheed Martin, U.S. Navy). For these components to be part of a plane, the manufacturer must prove the components were made the same way print-to-print regardless of the actual shape of the component being made. This dissertation focuses on the key metallurgical variable of temperature and explores how thermal energy is generated and where that energy goes in to the system. The key takeaway is, that without precise knowledge of the total heat generated and the entire thermal system, assurances about processing temperature cannot be made. An exploration of heat generation and metrics about its dispersion are presented. This is followed by a study on repairing structural components while changing the thermal system to understand its effects.

Yes / In this paper, an analytical model that represents the streamwise velocity distribution for open channel flow with submerged flexible vegetation is studied. In the present vegetated flow modelling, the whole flow field has been separated into two layers vertically: a vegetated layer and a non-vegetated free-water layer. Within the vegetated layer, an analysis of the mechanisms affecting water flow through flexible vegetation has been conducted. In the non-vegetated layer, a modified log-law equation that represents the velocity profile varying with vegetation height has been investigated. Based on the studied analytical model, a sensitivity analysis has been conducted to assess the influences of the drag and friction coefficients on the flow velocity. The investigated ranges of drag and friction coefficients have also been compared to published values. The findings suggest that the drag and friction coefficient values are non-constant at different depths and vegetation densities, unlike the constant values commonly suggested in literature. This phenomenon is particularly clear for flows with flexible vegetation, which is characterised by large deflection.