Neste trabalho foram conduzidos experimentos de laboratório no intuito de avaliar o efeito da textura superficial no desempenho de óleos lubrificantes aditivados e não aditivados. Os materiais envolvidos nos ensaios são referentes a materiais de anel e camisa de motores de combustão interna e as condições de superfície envolveram processamentos de lixamento e retífica, bem como texturização de microcavidades a laser. Os ensaios foram do tipo alternado, com regime limítrofe de lubrificação. Inicialmente foram feitas análises sobre a metodologia utilizada para o cálculo do coeficiente de atrito em ensaios alternados, mostrando que os valores fornecidos diretamente pelo equipamento (aqui chamados de coeficiente de atrito pico a pico) não foram efetivos para este estudo, pois apresentam alta dispersão entre as réplicas dos ensaios e não é representativo em termos de eficiência do tribossistema. Foram geradas microcavidades nas superfícies de alguns blocos de ferro-fundido mediante texturização a laser. Esta texturização gerou rebarbas que foram retiradas por um processo de lixamento. Com isso, uma parte dos resultados avaliou o efeito do lixamento nos parâmetros de rugosidade, no entanto que o processo acaba por aumentar os valores de raio de aspereza e reduzir a altura média dos picos. Por fim, ensaios com óleo sem aditivo tiveram formação de óxido em todas as condições de superfície, com pouca variação do coeficiente de atrito. Já nos ensaios com óleo aditivado, os resultados mostraram pouca influência das microcavidades e maior contribuição das características de picos (raio e altura) na formação de tribofilmes redutores de atrito (neste caso MoS2). / This work was conducted by experimental tests in order to evaluate the effect of surface texture on fully formulated oil and base-oil performance. In these tests, the materials were related to the piston ring and cylinder, in which surfaces were sanded, grounded and textured by laser. In addition, the tests were carried out by reciprocating movement and boundary conditions. A coefficient of friction study in reciprocating tests was performed, showing that peak-to-peak methodology does not represent properly the tribosystem efficiency. Burr was generated around the dimples (made by laser surface texturing), in which were removed by sanded process. The results showed that sanded process increased the peak radius and decreased the peak height. The results considering the base oil showed oxide formation on the surface in all the cases, occurring low variation of friction coefficient in the system. On the other hand, in the fully formulated oil results, the dimples had no influence on MoS2 formation; however, it was possible to see a strong relation with the radius and average height of the asperities.

Perception and sense of touch are extremely important factors in design, but until recently, the exploration of skin tribology related to tactility has been relatively untouched. In this emergence, skin-on-polymer interactions are becoming more widely investigated due to the prevalence of polymers in everyday life, and the ability to define these interactions in terms of tactility would be hugely beneficial to the engineering and design process. Previous work has investigated polymer textiles concerning tactility, examining environmental and material properties that affect skin on fabric coefficient of friction. In this study, similar friction procedure was used to compare coefficients of friction of a fingerpad across varying polymer fabrics. Forces were applied in both longitudinal and lateral directions, and it was discovered that force directionality greatly affects coefficient of friction. Specific causes have yet to be determined, but it is suspected that material weave and microscopic surface properties play a major role in this directional behavior. To complement these studies and relate them to tactility, trained human evaluators rated the samples against four tactile attributes: abrasiveness, slipperiness, sensible texture, and fuzziness. These ballots were then analyzed with Quantitative Data Analysis and shown to be repeatable among the participants, and each of the attributes were shown to be statistically independent of coefficient of friction. It should be noted, however, that fuzziness showed the greatest correlation coefficient of R^2=0.27. Material selection plays an integral role in frictional behavior, and researchers have been studying contact theory on both microscopic and macroscopic levels to determine how surface topography affects skin-polymer tribology. To negate material effects discussed in the Greenwood-Williamson contact model, frictional tests were performed on identical polypropylene plaques with textured grooves of varying dimensions. Both geometry and directionality proved to be major frictional contributors; as groove size increased, finger friction in the longitudinal direction decreased, but friction increased laterally. In addition to testing a fingerpad, friction was measured with a silicone wand to simulate a finger with different material properties. The silicone exhibited the opposite trend as skin; as groove width decreased, frictional forces increased longitudinally and decreased laterally. While topography affects frictional behavior, counterface stiffness, and intrinsic material properties may cause the trend shift between skin and silicone.

Copper polishing performance depends significantly on the properties of pads, slurries, conditioning, pressure, sliding velocity, slurry flow rate and temperature. A slight variance in each of these parameters will cause significant change in polising results. Various investigations are performed during this study to understand the effect of consumables and other main operating parameters on copper polishing in terms of removal rate, lubrication mechanism, and temperature transients. A modified two-step Langmuir-Hinshelwood removal rate model and a flash heating thermal model are developed to describe the removal mechanism.Results indicate that grain size plays an important role during copper polishing. Smaller grain size may enhance the chemical rate by providing a higher density of favorable reaction sites. However, denser grain boundaries due to smaller grain size may reduce the mechanical rate by increasing the probability of disruption of three body sliding contact. It is found that removal rate increases as slurry flow increases from 60 to 80 cc/min because higher slurry flow rate can provide more reactants to the system. Then removal rate decreases as slurry flow rate is further increased to 140 cc/min, which is due to synergic effects of the wafer temperature, slurry flow and slurry residence time under the wafer. The observed removal rate drop is thought to be due to the change of the wafer temperature at high sliding velocity.Experimental results from eight slurry formulations with various abrasize size and content show that in the case of 13-nm abrasives, the dominant tribological mechanism is that of partial lubrication, while in the case of 35-nm abrasives, the dominant tribological mechanism is that of boundary lubrication. COF values of the slurry with surfactant are generally lower that those of the slurry without surfactant.Logarithmic spiral positive pad, whose spiral groove is at a slight angle to the pad rotation direction, shows the highest average COF. The radial pad results in the smallest average COF. For all types of the grooved pads investigated, CMP is mechanically limited at low pV, and chemically limited at high pV. Non-Prestonian behavior is thought to be due to variations of COF and substrate temperatures.Dual Emission UV Light Enhanced Fluorescence results indicate that during polishing the wafer is tilted towards the center of the pad and that the extent of wafer tilt is a strong function of diamond disc pressure. Increasing the oscillation frequency of the diamond disc or the rotation rate decreases slurry film thickness. Slurry film thickness increases with the slurry flow rate. Also slurry film thickness strongly depends on diamond disc design.

The use of carbon-carbon (C/C) composites for clutch application requires a basic understanding of the structural characteristics of the composites that control their frictional and engineering properties. These are related to the microstructure of the matrix and fiber architecture, with the character of fiber/matrix interface and type of defects, porosity and microcracks being the most relevant. The purpose of this study is to examine and characterize the relation between the fiber architecture of selected C/C composites and its relation to their frictional properties when subjected to different normal forces and relative humidity. Friction tests is conducted using a Brüker Universal Friction Tester (UFT). This study also seeks to characterize and analyze the microstructure and fiber architecture through Polarized Light Microscopy, X-Ray Diffraction and Ultrasound Scans. This study shows that the Coefficient of Friction (COF) at constant normal force and RPM are always slightly lower for the samples with surface fibers orientated at 45° relative to the direction of rotation compared to samples with surface fibers orientated 0/90° at 50% relative humidity. The percent difference ranges from 1.62% to 15.30%. However, at 85% relative humidity, the average COF at the constant normal force and RPM are always slightly higher for the 45° compared to 0/90° samples for Rotor samples, while in contrast the average COF are always lower for the 45° samples compared to 0/90° samples for Stator samples. The percent difference ranges from 3.14% to 35.46%. This study found significant differences between the 0/90° samples and the 45° samples. There is indication that the fiber orientation can cause differences between frictional properties even if the clutches are made from the same material. The change in humidity also significantly changes the resulting COF.

Neste trabalho foram conduzidos experimentos de laboratório no intuito de avaliar o efeito da textura superficial no desempenho de óleos lubrificantes aditivados e não aditivados. Os materiais envolvidos nos ensaios são referentes a materiais de anel e camisa de motores de combustão interna e as condições de superfície envolveram processamentos de lixamento e retífica, bem como texturização de microcavidades a laser. Os ensaios foram do tipo alternado, com regime limítrofe de lubrificação. Inicialmente foram feitas análises sobre a metodologia utilizada para o cálculo do coeficiente de atrito em ensaios alternados, mostrando que os valores fornecidos diretamente pelo equipamento (aqui chamados de coeficiente de atrito pico a pico) não foram efetivos para este estudo, pois apresentam alta dispersão entre as réplicas dos ensaios e não é representativo em termos de eficiência do tribossistema. Foram geradas microcavidades nas superfícies de alguns blocos de ferro-fundido mediante texturização a laser. Esta texturização gerou rebarbas que foram retiradas por um processo de lixamento. Com isso, uma parte dos resultados avaliou o efeito do lixamento nos parâmetros de rugosidade, no entanto que o processo acaba por aumentar os valores de raio de aspereza e reduzir a altura média dos picos. Por fim, ensaios com óleo sem aditivo tiveram formação de óxido em todas as condições de superfície, com pouca variação do coeficiente de atrito. Já nos ensaios com óleo aditivado, os resultados mostraram pouca influência das microcavidades e maior contribuição das características de picos (raio e altura) na formação de tribofilmes redutores de atrito (neste caso MoS2). / This work was conducted by experimental tests in order to evaluate the effect of surface texture on fully formulated oil and base-oil performance. In these tests, the materials were related to the piston ring and cylinder, in which surfaces were sanded, grounded and textured by laser. In addition, the tests were carried out by reciprocating movement and boundary conditions. A coefficient of friction study in reciprocating tests was performed, showing that peak-to-peak methodology does not represent properly the tribosystem efficiency. Burr was generated around the dimples (made by laser surface texturing), in which were removed by sanded process. The results showed that sanded process increased the peak radius and decreased the peak height. The results considering the base oil showed oxide formation on the surface in all the cases, occurring low variation of friction coefficient in the system. On the other hand, in the fully formulated oil results, the dimples had no influence on MoS2 formation; however, it was possible to see a strong relation with the radius and average height of the asperities.

The ability of a lubricating oil to reduce friction in mechanical surfaces which are in relative sliding motion depends on the base oil behaviour. Previous studies have demonstrated that temperature has a significant influence on the friction behaviour of mineral and synthetic base oils by using a laboratory based friction testing machine. However, the effect of a constantly changing load under different temperature conditions has not been explored fully. In this study, the effect of an increasing load on the friction behaviour of four six different mineral base oils and a polyalphaolefin (PAO) base oil were studied using the SRV4® tribometer. The sliding surfaces were AISI 52100 steel ball and disc. The average loads (range: 50 – 250 N), temperatures (range: 40 – 120 oC), relative humidity of 20 % and a sliding speed of 0.2 m.s-1 were selected as the test conditions. The seven base oils were selected from four API base oil groups. Stribeck curves were used as a tool to characterize the friction behaviour of the base oils. The results show that for all the base oils, the coefficient of friction and the Stribeck parameter decrease gradually with the increase in applied normal load under constant temperature conditions. The increase in temperature increased the coefficient of friction and decreased the Stribeck parameter at each load stage. The external friction mechanisms dominated the friction behaviour under all test conditions. Viscosity showed a strong influence on the film forming characteristics of the seven base oils only at 40 and 60 oC. Between 80 and 120 oC, the oil-surface interactions were predominant. The results further demonstrated that effect of an increasing temperature on the coefficient of friction was bigger between 80 and 100 oC for all Group III base oils and was consistent between 40 and 120 oC for the Group III+ and PAO base oil. The highly saturated (PAO and Group III+) base oils have demonstrated good thermal stability and less reactivity compared to the less saturated base oils (GI and GIII) under all test conditions. The friction behaviour of the PAO base oil was the most affected by the presence of dissolved water. The presence of water proved to increase the friction at the sliding steel interfaces. / Dissertation (MEng)--University of Pretoria, 2018. / Chemical Engineering / MEng / Unrestricted

This thesis deals with the study of the effect of the constituents of the model synovial fluid on the frictional properties of articular cartilage. The influence of constituents, concentration, speed and load is observed. Experiments were performed on a commercial tribometer at configuration pin-on-plate. Several types of lubricants containing synovial fluid constituents have been selected for the experiments. Lubricants were prepared at two concentrations, the concentration of healthy individuals and at a concentration typical of for osteoarthritic patients. Speeds 5 and 10 mm/s and 5 and 10 N loads were used for all experiments. It is shown that when using only lubricant containing proteins, no difference in the coefficient of friction is observed and the effect of concentration is also not observed. The addition of hyaluronic acid has a synergistic effect with -globulin, however in the case of lubricants containing albumin, the effect is opposite. After the addition of phospholipids, no significant effect on friction is observed in -globulin containing lubricants. No significant effect of the composition and concentration of the lubricants is observed with the load change.

This thesis deals with tests of forming operations, which are used to determine coefficient of friction. In the theoretical part of thesis, the individual tests are described in details, with the greatest emphasis on the upsetting test. In the experimental part of thesis was perform upsetting test on the cylindrical and ring samples. Coefficient of friction of the cylindrical samples was determined by a calculation method and ring samples were evaluated using diagram of calibration. The thesis includes comparison of the result received on lubricant and unlubricated samples and method for determined coefficient of friction. Graphite Delta 144 was used as a lubricant. This result show that the lubricant has a positive effect on forming process.

Research has shown that older adults who have experienced a previous fall are 60-70% more likely to suffer future falls. A study was conducted to investigate if stress and anxiety associated with a fear of falling contributes to the increased incidents of falls among older adults. The investigation compared physiological parameters, with biomechanical parameters of walking for twenty-eight participants in two age groups: (18-35) and (65 or older). Both age groups were evaluated while walking over dry and slippery floor surfaces. Biomechanical parameters included: step length, required coefficient of friction (RCOF), slip distance, and heel contact velocity. Physiological parameters included: stress and anxiety. Overall, the results indicated that there were differences between older and younger adult's biomechanical parameters of walking, and their physiological stress and anxiety associated with an inadvertent slip. Younger adult's normal RCOF was higher and their normal step length was longer compared to older adults. Older adult's stress level after a slip was significantly higher than younger adults. However, younger and older adult's anxiety scores were not significantly different. Furthermore, younger and older adults modified their step length differently to avoid slipping, when walking over the slippery floor surface. It was concluded that some anxiety and stress may be beneficial in reducing the occurrence of inadvertent slips and falls due to an increased awareness of one's external environment. / Master of Science

This dissertation presents a series of studies relating to optimization of kinematics and consumables during chemical mechanical planarization processes. These are also evaluated with the purpose of minimizing environmental and cost of ownership impacts.In order to study diamond micro-wear and substrate wear during planarization processes, a series of static etch tests and wear tests were performed using different types of diamond discs and subjected to various treatments. Scanning Electron Microscopy (SEM) and Inductively Coupled Plasma Membrane Spectroscopy (ICPMS) were used to estimate the extent of diamond micro-wear and substrate wear.Next, the impact of various factors (type of slurry abrasive, pH, abrasive content and abrasive concentration) on pad wear rate during planarization process was studied. Another study in this dissertation focuses on the development of a novel technique of using coefficient of friction (COF) data to distinguish between good and bad diamond discs. This study made use of the innovative tool diamond disc dragging device (DDD-100) designed and developed for the purpose of this study.It is known that the performance of chemical mechanical planarization depends significantly on the polishing pad grooving type and the kinematics involved in the process. Variations in pad grooving type as well as pressure and sliding velocity can affect polishing performance. One study in this dissertation investigates the effect of pressure and sliding velocity on the polishing performance. The study is conducted on multiple pressure and sliding velocity variations to understand the characteristic of each condition. A subsequent study focuses on the impact of pad grooving type on polishing performance.The greatest contribution of this dissertation involves development of the novel slurry injector to optimize the utilization of slurry during planarization processes. Slurry is a critical component in chemical mechanical planarization processes and accounts for approximately 50 percent of the cost of ownership (CoO). The novel injector apart from reducing the consumption of slurry, also contributed in addressing problems associated with foaming, reduced the number of defects and achieved better within wafer non-uniformity (WIWNU).