Browsing by Subject "TRIBOLOGY"
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Item Static characteristics and rotordynamic coefficients of a four-pad tilting-pad journal bearing with ball-in-socket pivots in load-between-pad configuration(2009-05-15) Harris, Joel MarkStatic characteristics and rotordynamic coefficients were experimentally determined for a four-pad tilting-pad journal bearing with ball-in-socket pivots in loadbetween- pad configuration. A frequency-independent [M]-[C]-[K] model fit the measurements reasonably well, except for the cross-coupled damping coefficients. Test conditions included speeds from 4,000 to 12,000 rpm and unit loads from 0 to 1896 kPa (0 to 275 psi). The test bearing was manufactured by Rotating Machinery Technology (RMT), Inc. Though it has a nominal diameter of 101.78 mm (4.0070 in.), measurements indicated significant bearing crush with radial bearing clearances of 99.6 ?m (3.92 mils) and 54.6 ?m (2.15 mils) in the axes 45? counterclockwise and 45? clockwise from the loaded axis, respectively. The pad length is 101.6 mm (4.00 in.), giving L/D = 1.00. The pad arc angle is 73?, and the pivot offset ratio is 65%. The preloads of the loaded and unloaded pads are 0.37 and 0.58, respectively. A bulk-flow Navier-Stokes model was used for predictions, using adiabatic conditions for the bearing fluid. Because the model assumes constant nominal clearances at all pads, the average of the measured clearances was used as an estimate. Eccentricities and attitude angles were markedly under predicted while power loss was under predicted at low speeds and very well predicted at high speeds. The maximum detected pad temperature was 71?C (160?F) and the rise from inlet to maximum bearing temperature was over predicted by 10-40%. Multiple-frequency force inputs were used to excite the bearing. Direct stiffness and damping coefficients were significantly over predicted, but addition of a simple stiffness-in-series model substantially improved the agreement between theory and experiment. Direct added masses were zero or negative at low speeds and increased with speed up to a maximum of about 50 kg; they were normally greater in the unloaded direction. Although significant cross-coupled stiffness terms were present, they always had the same sign. The bearing had zero whirl frequency ratio netting unconditional stability over all test conditions. Static stiffness in the y direction (obtained from steadystate loading) matched the rotordynamic stiffness Kyy (obtained from multiple-frequency excitation) reasonably at low loads but poorly at the maximum test load.Item Tribological characterization of coatings and nanofluids(2009-05-15) Baxi, Juhi BhaskarAdvancement in biotechnology has successfully converted the conventional bearing couples into artificial joints. Materials used today, however, have not been satisfactory. Problems such as osteolysis and aseptic loosening lead to failure of artificial joints and also the lifespan of these joints is to be further improved. This research targets two issues related to the problem: coatings and design of new generation biofluids. Superior to metals and polymers, ceramics are hard and biocompatible and exhibit low wear and friction. The ceramic-on-ceramic bearing pair could last for a long time which could be beneficial to younger and active patients who need a bearing pair which would last for more than 15 years to avoid the possibility of a revision surgery. The first part of this thesis deals with studying the microstructure-property relationship of new ceramic-based materials and coatings. Specifically, alumina (ceramic) coatings at different current intensities were tested in order to determine their feasibility as a biomaterial for artificial joints. In order to find a new avenue for developing biofluids, the second part of this thesis focuses on the failure of artificial joints under inadequate lubrication. Also due to osteoarthritis, synthetic biofluid is injected into joints to help relieve pain but it works for only 6-9 months. We propose a new method using noble gold nanoparticles to modify fluids. This was accomplished by mixing different concentration of nanoparticles with biofluid. This thesis consists of 6 sections. The first section is an introduction to tribology, biotribology and artificial joints which is followed by the second section which discusses the objectives of the research. The third section describes the materials and methods used in the research. The tribological characterization of MAO alumina coatings is discussed in the fourth section and the fifth section discusses the effect of nanoparticles on fluid lubrication. The last section is the conclusion.