Master of Science / Department of Civil Engineering / Mustaque A. Hossain / Road surfaces may prematurely lose pavement friction due to polished aggregates on sharp horizontal curves, steep grades, or near intersections resulting in vehicle skidding. The problem gets exacerbated during wet weather. The Federal Highway Administration (FHWA) estimates that about 70% of wet pavement crashes can be prevented or minimized by improving pavement friction. High Friction Surface Treatment (HFST), a specially-designed thin surface application of hard aggregates and thermosetting resins like epoxy, has been proven to be an effective method to increase road surface friction. Calcined bauxite has been predominantly used in the United States as the hard aggregate in combination with an epoxy binder for HFST. However, this treatment is expensive since the calcined bauxite is imported. The objective of this study is to evaluate the performance of a local aggregate in HFST. Slab specimens of hot-mix asphalt (HMA) were compacted in the laboratory and treated with HFST systems incorporating both calcined bauxite and a local, hard aggregate, Picher Oklahoma flint aggregate. The treated HMA specimens were then tested with a Dynamic Friction Tester (DFT) and a Circular Track Meter (CTM) to determine the frictional coefficient and texture depth, respectively. Also, Hamburg Wheel Tracking Device Testing were conducted on these HFST systems to evaluate wearing resistance under repetitive wheel load. Field measurements of texture depths on HFST were also done. Statistical analysis was performed to compare the performance of high friction surfaces prepared with different aggregate epoxy combinations. The results show that flint aggregate can be a suitable substitute for the calcined bauxite in HFST. Field measurements also showed marked improvements in texture depth with HFST.

Made available in DSpace on 2014-10-09T12:25:56Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:01:50Z (GMT). No. of bitstreams: 1 11273.pdf: 2821885 bytes, checksum: 146c300ba4598f02a259aa3fe860b0c6 (MD5) / Dissertacao (Mestrado) / IEA/D / Instituto de Energia Atomica - IEA

Este trabalho apresenta o desenvolvimento de um tribômetro para a realização de ensaios com materiais de fricção utilizados em freios veiculares, capaz de servir como uma ferramenta adicional para pesquisa e desenvolvimento de novos produtos. São apresentadas todas as etapas de desenvolvimento da máquina, desde suas premissas básicas, projeto mecânico e de automação e procedimento de calibração até os testes finais para comprovação das suas potencialidades. Construiu-se um equipamento de pequeno porte (dimensões reduzidas), a fim de permitir ensaios rápidos e de baixo custo. O sistema atuador e de rotação foi dimensionado a partir de faixas de velocidade e pressão de contato que ocorrem em sistemas de freio comerciais. O tribômetro permite a troca rápida dos corpos de prova além do ajuste do raio de deslizamento do par de atrito. Além disso, um mecanismo de atuação próprio permite a realização de ensaios sem a influência do tipo de sistema de freio empregado. O sistema de automação, composto por hardware para aquisição de dados e programa para gerar interface gráfica, gerencia todos os processos envolvidos na máquina, além de tornar a sua operacionalidade simples e racional. Um conjunto composto por resistência aquecedora, soprador de ar, relé e termopares é responsável por controlar a temperatura do disco, separando esta variável dos demais parâmetros de operação (pressão e velocidade de escorregamento) durante os ensaios. O procedimento de calibração adotado mostra que o equipamento projetado fornece medições confiáveis da força normal, do torque de frenagem e, conseqüentemente, do coeficiente de atrito. Testes de avaliação do sistema atuador apontam que a força medida sofre a influência da rugosidade do disco, da baixa capacidade do reservatório de ar do sistema pneumático, de efeitos de histerese mecânica e da dilatação térmica e de ruídos eletromagnéticos. Os resultados dos ensaios de frenagem empregados comprovam que a máquina projetada é capaz de separar a variável temperatura do disco dos demais parâmetros de operação e, desta forma, pode servir de ferramenta adicional na compreensão do comportamento do atrito (e do desgaste em um momento posterior) frente às diferentes condições de operação contribuindo, de certa forma, para o aumento do conhecimento dos fenômenos tribológicos. / This work presents the development of a tribometer for friction tests with materials used in vehicular brakes, able to serving as an additional tool for research and development of new products. Every stage of the project are presented since its basic premises, mechanical and automation design, the calibration procedure until the final tests to prove its potential. It was constructed an equipment with small dimensions to enable rapid and low cost testing. The actuator and rotation system has been designed to operate in the range of velocity and contact pressures that occur in commercial brake systems. The tribometer allows the rapid exchange of specimen beyond the adjustment of the wear track radius. Furthermore, a special mechanism of action was designed to allow testing without the influence of the type of brake system employed. The automation system, composed of a data acquisition hardware and software to generate graphical interface, manages all processes involved in the machine, and makes its operation simple and rational. A set composed of heating resistance, air blower, relay and thermocouples is responsible for controlling the temperature of the disk, separating it from other variable operating conditions (pressure and slip velocity) during tests. The calibration procedure performed show that the equipment designed provides reliable measurements of normal force, braking torque and friction coefficient. The tests for evaluating the system actuator suggest that the force measurement has influence of the disk surface roughness, of low air capacity in the tank, of thermal dilation and mechanic hysteresis effects and of electromagnetic noise. The results of braking tests performed show that the designed machine is capable of separating the variable disk temperature of the other operation parameters and thus can serve as an additional tool in understanding the friction behavior (and wear a moment later) under a set of operating conditions. It can contribute, in some way, to enlarge the knowledge with respect to tribologics phenomenons.

Este trabalho apresenta o desenvolvimento de um tribômetro para a realização de ensaios com materiais de fricção utilizados em freios veiculares, capaz de servir como uma ferramenta adicional para pesquisa e desenvolvimento de novos produtos. São apresentadas todas as etapas de desenvolvimento da máquina, desde suas premissas básicas, projeto mecânico e de automação e procedimento de calibração até os testes finais para comprovação das suas potencialidades. Construiu-se um equipamento de pequeno porte (dimensões reduzidas), a fim de permitir ensaios rápidos e de baixo custo. O sistema atuador e de rotação foi dimensionado a partir de faixas de velocidade e pressão de contato que ocorrem em sistemas de freio comerciais. O tribômetro permite a troca rápida dos corpos de prova além do ajuste do raio de deslizamento do par de atrito. Além disso, um mecanismo de atuação próprio permite a realização de ensaios sem a influência do tipo de sistema de freio empregado. O sistema de automação, composto por hardware para aquisição de dados e programa para gerar interface gráfica, gerencia todos os processos envolvidos na máquina, além de tornar a sua operacionalidade simples e racional. Um conjunto composto por resistência aquecedora, soprador de ar, relé e termopares é responsável por controlar a temperatura do disco, separando esta variável dos demais parâmetros de operação (pressão e velocidade de escorregamento) durante os ensaios. O procedimento de calibração adotado mostra que o equipamento projetado fornece medições confiáveis da força normal, do torque de frenagem e, conseqüentemente, do coeficiente de atrito. Testes de avaliação do sistema atuador apontam que a força medida sofre a influência da rugosidade do disco, da baixa capacidade do reservatório de ar do sistema pneumático, de efeitos de histerese mecânica e da dilatação térmica e de ruídos eletromagnéticos. Os resultados dos ensaios de frenagem empregados comprovam que a máquina projetada é capaz de separar a variável temperatura do disco dos demais parâmetros de operação e, desta forma, pode servir de ferramenta adicional na compreensão do comportamento do atrito (e do desgaste em um momento posterior) frente às diferentes condições de operação contribuindo, de certa forma, para o aumento do conhecimento dos fenômenos tribológicos. / This work presents the development of a tribometer for friction tests with materials used in vehicular brakes, able to serving as an additional tool for research and development of new products. Every stage of the project are presented since its basic premises, mechanical and automation design, the calibration procedure until the final tests to prove its potential. It was constructed an equipment with small dimensions to enable rapid and low cost testing. The actuator and rotation system has been designed to operate in the range of velocity and contact pressures that occur in commercial brake systems. The tribometer allows the rapid exchange of specimen beyond the adjustment of the wear track radius. Furthermore, a special mechanism of action was designed to allow testing without the influence of the type of brake system employed. The automation system, composed of a data acquisition hardware and software to generate graphical interface, manages all processes involved in the machine, and makes its operation simple and rational. A set composed of heating resistance, air blower, relay and thermocouples is responsible for controlling the temperature of the disk, separating it from other variable operating conditions (pressure and slip velocity) during tests. The calibration procedure performed show that the equipment designed provides reliable measurements of normal force, braking torque and friction coefficient. The tests for evaluating the system actuator suggest that the force measurement has influence of the disk surface roughness, of low air capacity in the tank, of thermal dilation and mechanic hysteresis effects and of electromagnetic noise. The results of braking tests performed show that the designed machine is capable of separating the variable disk temperature of the other operation parameters and thus can serve as an additional tool in understanding the friction behavior (and wear a moment later) under a set of operating conditions. It can contribute, in some way, to enlarge the knowledge with respect to tribologics phenomenons.

Made available in DSpace on 2014-10-09T12:25:56Z (GMT). No. of bitstreams: 0 / Made available in DSpace on 2014-10-09T14:01:50Z (GMT). No. of bitstreams: 1 11273.pdf: 2821885 bytes, checksum: 146c300ba4598f02a259aa3fe860b0c6 (MD5) / Dissertacao (Mestrado) / IEA/D / Instituto de Energia Atomica - IEA

Une assemblée d’objets solides de taille typique d’une fraction de millimètre n’est pas sensible à l’agitation thermique. En effet, ces éléments sont trop massifs pour être mis en mouvement par le chaos moléculaire. Cependant, un tel empilement est susceptible de se réorganiser sous la seule influence des variations de température ambiante. Ces dernières induisent des changements de longueur certes relativement petits (coefficient de dilatation typique de l'orde de 10-5 K-1) mais, compte tenu de la rigidité de ces matériaux (module d’Young de l’ordre de 1011Pa), les déformations associées sont suffisantes pour créer des efforts capables de déplacer des grains de manière irréversible. Nous étudions expérimentalement la compaction d’une colonne de billes de verre soumise à des cycles de température. Imposer les variations de température par un fil tendu placé au centre de la colonne et alimenté par un courant sinusoïdal de fréquence assez haute permet de minimiser les effets de la dilatation du récipient. La dynamique du système est étudiée en fonction des caractéristiques du chauffage et des conditions mécaniques. Par ailleurs, d'un point de vue théorique, nous nous intéressons aux effets des variations de température sur un système discret modèle, des patins liés par des ressorts en contact frictionnel avec un plan incliné. Nous étudions l’influence de l’angle d'inclinaison et des caractéristiques des variations de température sur la reptation du système. Nous observons que proche d’une amplitude critique, entre mouvement et arrêt du système, ce dernier exhibe une dynamique intermittente. / An assembly of solid objects of typical size, a fraction of a millimeter is not sensitive to thermal agitation. Indeed, these elements are too massive to be moved by the molecular chaos. However, such a stack is likely to reorganize under the influence of ambient temperature variations. The latter lead to changes in length relatively small (coefficient of expansion typical of order 10-5 K-1), but, due to the rigidity of these materials (Young's modulus of about 1011Pa) deformations associated are sufficient to create stresses capable of moving grain irreversibly.We study experimentally the compaction of a column of glass beads subjected to temperature cycles. The temperature variations imposed by a stretched wire placed at the center of the column supplied by a high frequency sinusoidal current minimize the effects of expansion of the container. The dynamic of the system is studied for different heating and mechanical conditions.Moreover, from a theoretical point of view, we consider the effects of temperature variations on a discrete model system, sliders connected by springs in frictional contact with an inclined plane. We study the influence of the inclination angle and the characteristics of temperature variations on the creep of the system. We observe that close to a critical amplitude, between motion and rest, the system exhibits an intermittent dynamic.

Dans cette thèse, nous nous intéressons à l’adhésion d’élastomères sur des substrats rigides (interactions de van der Waals). Nous revisitons ainsi, en nous appuyant sur une approche expérimentale, deux situations classiques qui permettent la mesure de l’énergie d’adhésion. Dans une première partie dédiée à l’étude du pelage, nous montrons que le frottement peut modifier le processus de détachement d’une bande d’élastomère. Ceci est tout d’abord mis en évidence lors du pelage parallèlement à l’interface, où nous montrons qu’il conduit à la progression d’une zone de frottement jusqu’au détachement de la bande pour une force proportionnelle à l’aire de contact. Nous généralisons par la suite nos résultats au pelage selon un angle quelconque. En particulier, nous montrons comment la dissipation par frottement peut augmenter de façon significative la force de pelage pour des angles faibles. Dans une deuxième partie, nous nous tournons vers la mesure d’adhésion dans une géométrie JKR, c’est à dire lors de l’indentation d’une sphère élastique adhésive avec un substrat rigide. Nous utilisons des coques élastiques dont la réponse mécanique est beaucoup plus souple bien que plus complexe. Nous montrons qu’il est néanmoins possible d’obtenir une mesure de l’adhésion par une méthode très simple et très robuste, puisqu’elle ne suppose pas de connaissance a priori de la mécanique du système. Nous espérons que cette technique permettra dans le futur d’accéder à des énergies d’adhésion très faibles ou mettant en jeu des tissus biologiques particulièrement mous. / In this thesis, we are devoted to study the adhesion of elastomers to rigid substrates through van der Waals interactions. We review, from an experimental point of view, two classical methods to measure the adhesion energy. A first part is dedicated to the study of the peeling system, we show that friction can modify the detachment process of an elastomer strip. This is firstly observed in the lap-test configuration, where a sliding front propagates on the interface up until the end of the strip, for a pulling force proportional to the initial contact area. We generalize this results for the finite peeling angle case. In particular, we show how the friction dissipation significantly increases for small peeling angles. In the second part, we study the adhesion measure in the JKR geometry, i.e. for the indentation of an adhesive elastic sphere into a rigid plate. We use elastic thin shells, which elastic response is much softer, as well it is much more complex. However, it is possible to measure the adhesion energy through a very simple and robust method with no need of much details of the mechanical response of the system. We hope this technique will allow to measure the effect of very weak and sensitive adhesive systems such us biological tissues which are particularly soft.

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.

Perforated tubes are widely used in industry for various applications. A special application arises when there is fluid injection into the perforated tube. Such cases arise when perforated tubes are used for horizontal oil well drilling and French drains. The behaviour of the flow under these conditions has led to the development of correlations, which consider the effects of the perforations and injection process. However, there are few friction factor correlations in literature, which consider the increased kinetic energy at the perforated tube outlet caused by fluid injection and acceleration. The current study reports experimental correlations for determining the friction factor of perforated tubes when the additional kinetic energy from the injection process is considered. The friction factor measurements were conducted in copper tubes with an internal diameter of 20.8 mm and a wall thickness of 1 mm at three nondimensional pitches of 0.375, 0.75 and 1.5. A perforated length-to-diameter ratio of 40:1 was used for the perforated tubes. A perforation row contained seven small perforation holes with a diameter of 1.5 mm spaced evenly around the perimeter of the tube. These perforation rows were staggered row to row, resulting in triangular perforation patterns. Water was used as a test medium with Reynolds numbers at the tube outlet ranging from 20 000 to 60 000. The injection ratio was varied from 0 to 5% to obtain a total of 135 unique combinations of perforated tube friction factor data at different injection ratios, Reynolds numbers and nondimensional perforation pitches. The experiments were condensed into friction factor correlations, which allow perforated tube parameters to be optimisation for minimising pressure losses encountered in draining operations. Copyright / Dissertation (MEng)--University of Pretoria, 2011. / Mechanical and Aeronautical Engineering / unrestricted

Weld quality in the context of process control and internal conditions is studied. Several different alloys are welded including plain carbon steel, high-temperature steels, and several traditional and advanced superalloys. Across all studied weld systems, the following conditions led to stronger welds: higher forces and feedrates, lower temperatures, and moderate or limited upsets. In the best cases, post-weld strengths were nearly equal to basemetal strength. Tradition holds that large and symmetric upsets are necessary for good welds, but this study contradicts that notion. The fundamental requirements for bonding are two sufficiently clean surfaces in intimate contact. Only minimal upset is necessary to achieve that. In welding alloy 718, only 1 mm of feed (or ~0.4 mm of sample upset) was necessary to achieve $>$95\% of basemetal strength. In an advanced superalloy with low ductility, very low upsets were required in order to achieve high joint strength. For this low-ductility alloy, using a containing geometry increased both the internal pressure and ductility of this alloy, leading to a much larger window of sound welding conditions and stronger welds overall. In several dissimilar alloy systems, the relationship between force/feedrate and upset asymmetry varied between each alloy, but a more symmetric upset did not correlate to stronger welds. Advanced process control in FW was also performed with closed-loop temperature control and open-loop predictive cooling rate control. Using this technique, martensitic microstructures associated with a fast natural cooling rate were avoided, and a pearlitic microstructure was obtained. The yield and tensile strength of the weld was not adversely affected, and both were within range of published values for the basemetal.