Over the years, different lubricants have been used to operate hip simulators. The current applicable ISO standard (ISO 14242-1:2002) recommends the use of 25% calf serum diluted with deionised water. The standard further recommends that the fluid be changed and the acetabular cup be weighed every 500 000 cycles. This procedure results in a loss of both the third body wear particles and the wear pattern. The purpose of this study was to develop a synthetic lubricant that would map the viscosity and lubricity properties of joint fluid (“synovial fluid”) over the whole duration of a simulator test, which is typically five million cycles. The first objective of this study was to find the effect of temperature increase on the viscous and lubricative properties of joint fluid retrieved from both primary and revision patients prior to surgery. The lubricity tests were done on a Linear-Oscillation Test Machine (SRV machine). Three test temperatures were used namely 38ºC, 50ºC and 60ºC. The load at failure and the average coefficient of friction were parameters measured during these tests. A decrease in the load at failure was found for an increase in test temperature, while the coefficient of friction stayed relatively stable. The viscosity tests were done using a Brookfield Viscometer. The three test temperatures mentioned above, were copied. The joint fluid tested showed pseudoplastic flow behaviour. An increase in the viscosity as a function of test temperature increase and a magnitude of shear rate was observed. The second objective of this study was to develop a synthetic lubricant that had the same average properties than that found for the retrieved joint fluid. A mixture of three different chemicals, namely Poloxamer 188, Xanthan Gum and Lube Boosterâ II was used to map the viscous and lubricative properties of the joint fluid. A comparative test using the synthetic lubricant and bovine serum was performed in a custom-built simulator. Wear debris was sampled at 500 000 cycle intervals up to 4 500 000 cycles. During these intervals the bovine serum stations were drained and washed with deionised water, but not stripped and weighed as specified in the ISO standard. This was done intentionally to preserve the wear pattern during the entire test. The synthetic lubricant stations were not stripped or drained during these intervals. This ensured that the wear pattern was maintained and that the effect of accumulative wear could be investigated throughout the duration of the test. The wear debris from the test was then compared to wear debris retrieved from scar tissue of revision patients. The wear debris that was found in the scar tissue retrieved from patients was similar in shape and size to that which was found in the simulator using bovine serum and the synthetic lubricant. It can thus be concluded that an acceptable lubricant had been developed to replace the current test medium in the simulators. / Dissertation (MEd (Mechanical Engineering))--University of Pretoria, 2006. / Mechanical and Aeronautical Engineering / unrestricted

The high frequency reciprocating rig (HFRR) is typically used to determine the lubricity of diesel fuels and has been accepted as the universal test apparatus in most countries of the world. A study was undertaken to analyse results obtained with the HFRR instrument by identifying crucial factors contributing to friction and wear mechanisms during a lubricity test under given conditions that may lead to a better understanding of test results obtained. The transient temperature distribution on a semiinfinite disk due to a circular continuous oscillatory heat source was also modelled. The model was used to calculate the contact temperature of a contact similar to what can be expected in the HFRR apparatus. For lubricated tests a mixture of n-hexadecane (cetane) as base fluid and palmitic acid as lubricity additive was used. Experimental results, including results obtained by running unlubricated (dry) tests and results obtained from literature were all considered to formulate the hypothesis that a fully functional additive film will not survive the full duration of the lubricity test, which is 75 minutes (ISO 12156-1, 2003). Friction values obtained in the experiments conducted were much higher than what is expected for boundary films formed by long chain carboxylic acids. Comparable friction values were obtained in the first few seconds of the tests, but the friction values increased indicating the destruction of the boundary film. Metal oxide lubrication dominates for the remainder of the test. Information of the exact mechanism prevailing in the crucial first few seconds of the test should be obtained by increasing the data acquisition rate of the apparatus. It is believed that junction growth through adhesion is the dominant factor in the initial stages of the test. GCxGC/TOF-MS showed the formation of hexane and heptane, which is a strong indication of the catalytic decomposition of the C16-hydrocarbons in the sample. / Dissertation (MEng)--University of Pretoria, 2010. / Chemical Engineering / unrestricted

The examination of the application and accuracy of optical sensors for the purpose of determining rail lubricity of top-of-rail friction modifier is investigated in this research. A literature review of optical sensors as they relate to detecting thin layers is presented, as well as a literature review of the significant aspect of surface roughness on optical signature. Both commercially available optical sensors and optical devices, such as independent lasers and detectors, are examined in a comprehensive parametric study to determine the most suitable configuration for a prototype with adequate third-body detection. A prototype is constructed considering parameters such as sunlight contamination, vibrations, and angle of detection. The prototype is evaluated in a series of laboratory tests with known lubricity conditions for its accuracy of measurements and susceptibility to environmental conditions, in preparation for field testing. Upon field testing the prototype, the data indicates that it is capable of providing subjective measurements that can help with determining whether a rail is highly lubricated or unlubricated, or it is moderately lubricated. It is anticipated that the device could be used to provide a rail lubricity index. The investigation of the optical response of a rail in various conditions, including top-of-rail friction modifier presence and underlying surface roughness, reveals the behavior of friction modifying material on rail/wheel interactions. It is determined that surface roughness is imperative for distinguishing between scattering due to surface condition and scattering due to third-body layers. Additionally it is revealed that friction modifying materials become entrapped within the surface roughness of the rail, effectively causing a "seasoning" effect instead of a simple third body layer. This provides some explanation on the inadequacy of determining lubricity conditions using contacting methods since they cannot detect the entrapped material that are revealed only when the top of rail undergoes a micro deformation due to a passing wheel. Furthermore, the fluorescent signature of flange grease can be utilized to detect any flange grease contamination on top of rail. The results of the study indicate that it is possible to have practical optical sensors for top-of-rail third body layer detection and any contamination that may exist, initially through spot checking the rail and eventually through in-motion surveying. / Master of Science

The lubricants that are applied during metal cutting acts on the interface between the tool and the nascent surfaces generated by the cutting process. Dispersions of oil in water made using suitable emulsifier(s) are used as metal cutting lubricants. The efficiency of the emulsion in rendering a low friction layer on the freshly cut surface will depend on the composition of the emulsion and on the speed, load and temperature characteristics in the tribological system. A unique tribometer which can perform friction testing on freshly cut surfaces has been designed and built for the experimental investigation. In this experimental facility experiments are conducted by performing cutting operation inside a pool of the lubricant and friction force is measured in-situ. Experiments at different loads and speeds were performed. The surfaces were subsequently subjected to spectroscopic analysis using X-ray Photoelectron spectroscopy and Fourier Transform Infrared Spectroscopy (FTIR). Lubricity of the base oils on nascent and preformed (oxidized) surfaces are compared by performing friction tests on surfaces which are cut and friction tested without exposing them to the environment, and on surfaces which were cut and exposed to the environment. While the freshly cut surfaces were seen to be sensitive to the structure of the base oil, the oxidized surfaces did not differentiate between the oil structures. Amongst the three base oils tested, aromatic oil was found to exhibit the least friction. This is attributed to tendency of the aromatic chains to react with the surface and form a film, due to the formation of radical anion-metal cation complexes. Results from spectroscopic investigations are presented to substantiate these arguments. The thesis then explores the differences in the tribological behavior promoted by an emulsion between, when it acts on a cut surface and is slid just once, and when it acts on a cut surface slid repeatedly. Due to repeated sliding, friction was found to decrease with sliding time (distance), and the transition from a freshly formed surface to a repeatedly slid one was found to follow a smooth transition. The improvement in lubricity is attributed to the formation of carboxylate type structures (C=O) which get generated due to the tribological action under repeated sliding conditions in the presence of water. Under repeated sliding conditions, the friction as a function of emulsifier concentration is found to exhibit a minimum at a value which is much below the critical micellar concentration of the emulsifier (CMC). However, the variation under continuous cutting followed a different pattern, with the friction undergoing a sharp decrease close to the CMC. The effect of speed on the tribological performance was investigated and friction was found to increase dramatically beyond a critical speed which is marked as the onset of starvation. The characteristic time required for a film to develop on a newly created surface, together with the contact pressure conditions dictated by the load and speed dictates starvation. The films formed at speeds corresponding to starvation conditions was found to have a significantly different chemical structure from that corresponding to a speed less than the starvation speed.. The effect of temperature was found to affect the lubricity adversely. At elevated temperature, the nature of the film was found to change to that to starved condition, even at a speed which does not register starvation when operating at a lower temperature. The effect of solubility of the emulsifier on the friction characteristics were explored by using emulsifiers of varying hydrophilic-lypophilic values (HLB). Lower HLB emulsifiers were found to exhibit lesser friction, than those corresponding to high HLB value. The variation in lubricity is examined in the light of the morphology of the micellar structures which evolve using these emulsifiers. The main conclusions of the thesis are: 1 Evaluation of lubricity of metal cutting fluids warrants a testing strategy which tests their lubricity on freshly cut surfaces. 2 The formation of carboxylate structures aids lubricity while using an emulsion; emulsions which can result in the formation of such structures exhibit better lubricity under cutting conditions. 3 Tribofilms which show characteristic peaks related to chemisorbed oxygen is found to exhibit good lubricity under the test conditions. 4 Emulsifiers which form lamellar micellar structures which aid easy shear give better lubricity in cutting than those which yield spherical micelles.

This research serves to evaluate the ability of optical detection techniques to ascertain the lubricity of revenue service track from a moving platform for railroad applications. A literature review is presented that covers the rail vehicle dynamics that drive the need of Top-of-Rail lubrication and directly affect the manner in which the Top-of-Rail Friction Modifiers (TORFM) and flange grease both spread down rail and eventually wear away. This literature review also highlights previous research in the field of rail lubrication and the benefits that rail lubricants, specifically TORFM, provide for the railroads. Finally, the literature review covers the governing optical principals inherent to the synchronous spot radiometer that has been developed for use in the research as a gloss ratio instrument and also addresses the drawbacks and challenges inherent to applying this type of instrument in the railroad industry. The research then overviews previous rail lubricity sensors developed by the Railway Technologies Laboratory (RTL) at Virginia Tech and the lessons learned from their application. The preceding field testing conducting with a modified second generation rail lubricity sensor and a rail push car is briefly summarized with emphasis on the drawbacks and issues that were used to develop the third generation sensor used for this research. The development of the third generation sensor is covered, including the issues that it attempts to solve from its predecessor and the governing optical principals that govern the operation of the sensor. The laboratory evaluations conducting to commission the sensor are also covered in preparation for deploying the new third generation sensor in medium speed, medium distance revenue service testing. This includes a shakedown run on a siding in Riverside, VA prior to conducting mainline in-service testing. Finally, this research thesis covers the in-service testing on revenue track conducted with the new third generation rail lubricity sensor and the accompanying remote-controlled (RC) rail cart. The two components, when combined, create a Lubricity Assessment System which is capable of being operated at speeds upwards of 10 mph remotely from a follow hy-rail truck. The data collected from this field test is analyzed for the lubricity assessments that are able to be drawn from this initial phase of field service testing. The conclusions from this testing affirm the ability of optical methods to determine and evaluate Top-of-Rail (TOR) lubricity from a moving platform. Specifically, the new sensor is able to identify several local phenomena that demonstrate the high potential for errant evaluation of rail lubricity evaluation from spot check based methods that are solved by evaluating the track in a continuous, moving fashion. Based on the continuous moving data collected for this test, several new signal traits such as the spatial frequency (wavenumber) associated with the passing freight cart wheels in the lubricity signal and the phantom applicator effect of transient lubricity conditions at the entrances and exits of curves can be detected and investigated. The success of this research indicates the continued evaluation of lubricity signals from a moving platform is warranted and suggests the potential for introducing one of these systems to various track metrology cars deployed throughout the United States railroads. / Master of Science / The United States railroads have been employing rail lubricants to the rails since the beginning of the industry and have recently, in the past 20 years, introduced another type of lubricant: Top-of-Rail Friction Modifiers (TORFM). TORFM creates a third body layer between the train wheels and the Top-of-Rail surface to minimize asset wear of both the wheel and rail and to increase the train efficiency. As the United States railroads embrace Precision Scheduled Railroading (PSR), increased train efficiency can allow the railroads to run longer trains with fewer locomotives. This increases the efficiency and capability of the rail network and also decreases the fuel burned and the amount of rail and wheel wear. TORFM has been proven to be effective and is widely adopted, but the railroads are still in need of tools to determine the presence and absence of these thin and often nearly invisible layers of lubricant on the rail surface. This research uses lasers as tool to quantify the level of lubrication of the rail surface. The presence of rail lubricants, such as TORFM, on the rail surface change the amount of light that is reflected and scattered off the shiny steel surface. These changes are often small but can be captured by photodetectors housed in the instrument. By plotting the detected sensor values, trends in the lubricity signal can be tracked and evaluated to determine the presence or absence of rail lubricants and assess the overall quality of lubrication on the rail at specific locations down track. The research in this thesis takes existing methods that were used for single spot inspections and adapts them to a moving platform. The moving platform is able to continuously scan the Top-of-Rail surface as the instrument moves along and generates continuous moving evaluations of rail lubricity. This can be especially important when the lubricity is not uniform and allows for trends in the data to be analyzed to provide more consistent and precise evaluations of the lubricity trends down rail. Optical tools like this sensor, which are by nature non-contact sensors, can easily be adapted to existing track measurement railcars and deployed system wide. This solves a strong need for railroad engineers: to be able to identify the presence of rail lubricants and evaluate the effectiveness of their lubrication practices.