No description available.

No description available.

The goal of this work is to investigate the physical mechanisms that distress thrust washer bearings through physical modeling and numerical techniques. The thrust washer bearing is subjected to non-axisymmetric loads within the planetary gear sets of automatic transmissions in automobiles. In practice the thrust washer bearing often distresses severely and unpredictably, causing transmission breakdown and liability issues. A specially designed thrust washer bearing test rig allows for controlled variation of the operational parameters (speed, load, lubrication flow rate, etc.) governing the tribological behavior of the washer. The test rig also records pertinent real-time data (frictional torque and temperature) from the bearing. In conjunction with the experimental model, a new comprehensive numerical simulation of thrust washer bearings is constructed. The numerical simulation incorporates the effects of macro-scale deformation, micro-scale surface asperity contact, heat generation, boundary and full film lubrication. To model surface asperity contact, the current work performs an extensive finite element study of elasto-plastic spherical contact. The numerical and experimental results show that significant sliding asperity contact can cause high temperatures, high friction, and severe wear.

Abstract The tool wear characteristics of the hydrodynamic polishing process under various lubricating conditions are examined in this study. Both the experimental and theoretical studies will be done in this paper. In the experimental study, the relationships between tool wear and its possible influential factors will be examined. In the theoretical study, the mathematical model will be established to interpret the qualitative and quantitative relationships between tool wear characteristics and various operating parameters. For the experimental study, a series of experiments will be done to investigate the effect of various factors on the tool wear and machining rate, under non-contact or semi-contact lubricating condition. The factors may include the tool¡¦s angular speed, the applied load, the tool¡¦s surface irregularities, the slurry viscosity, and the properties of tool, workpiece and abrasive particle (such as surface energy). To establish the mathematical model, the principle of dynamics, law of minimum potential energy and elasto-hydrodynamic lubricating theorem of hydrodynamic polishing process are adopted to derive the removal rate model of a particle under differential contact conditions or under various material parameters (such as surface energies or speed constants) from the energy point of view. In addition, the wear rate of tool is to be analyzed. To deal with the random nature of tool¡¦s surface irregularities, the probability theory is applied to calculate the average wear rate of tool, under semi-contact or non-contact condition or under various material parameters. It is shown that both the tool waviness and radius of tool curvature changed and had specific trends in the wear process. Especially, the wear rate of tool under semi-contact lubricating condition was not necessarily large than that under the non-contact one. The experimental data indicated that the effects of tool wear on machining rate highly depended on the lubricating condition of tool. The trend of machining rate versus accumulated machining time under non-contact lubricating condition was very different from that under the semi-contact one. A mathematical model relating the removal capability of an abrasive particle at the tool¡¦s or workpiece¡¦s surface and various operating parameters are proposed. The qualitative properties of removal capability the under different material parameters and various contact conditions are obtained by the computer simulations. The analysis indicates that the relationships between the removal capability and various material parameters (such as surface energies of adhesion or operating conditions) are not monotonic. Under the contact condition, it is shown that the tool¡¦s surface energy of adhesion and the speed constant has a negative effect on the removal capability at tool¡¦s surface. On the other hand, the surface energy of adhesion on work and the speed constants have a positive effect on the removal capability at tool¡¦s surface. For the workpiece, the converse implications are also true. Three types of patterns for removal capability at tool¡¦s surface due to the degree of embedding of a particle were obtained. There are increase or first increase then decrease or decrease directly, respectively. Under non-contact condition, it is shown that the removal capability has a negative relationship with local film thickness. In addition, a mathematical model relating the tool or work piece wear rate and various operating parameters are also proposed. The qualitative properties of tool wear rate under various lubricating conditions are obtained by the simple statistic analysis. The analysis indicates that the relationships between tool and workpiece wear rate and various parameters are also not monotonic. Under non-contact condition, the tool or workpiece wear rate will first increase then decrease due to the tool periphery speed increase. The magnitude of wear rate will decrease or increase due to the material parameters. Under the semi-contact condition, the up-and-down trend is also occurred in the relationship between tool or workpiece wear rate and the tool periphery speed. Accordingly, the relationships between wear rate and tool periphery speed, in a lubricating range covering the non-contact and semi-contact conditions, will reveal a twin-peak pattern. Generally, the workpiece wear rate under the semi-contact condition is not less than the non-contact one. However, the tool wear rate under the semi-contact condition is not necessarily large than the non-contact one. For a specific condition, under the semi-contact condition, the magnitude of the tool wear rate under different speed will increase or decrease by choosing different tool¡¦s surface adhesive energy and speed constant and the relationship between tool wear rate and tool speed will become complex. The wear rate could increase or decrease significantly. In other word, the tool wear rate under the semi-contact condition may be smaller or large than the non-contact one. Hence, a tool with large surface adhesive energy and speed constant should have a lower tool wear rate or higher work wear rate under certain lubricating regime. Finally, the experimental study tests that the proposed model is closely related with the experimental data. The study showed that the qualitative trends of experimental data are consistent with the analytical predictions. Some of the qualitative relationships between tool wear and machining rate could be properly explained from the elasto-hydrodynamic lubrication theorem and the proposed wear theorem for hydrodynamic polishing process.

Thesis (M.S.)--West Virginia University, 2003. / Title from document title page. Document formatted into pages; contains ix, 73 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 72-73).

The aim of this thesis was to design, develop and evaluate a Non-Contact Corneal Aesthesiometer (NCCA), using a controlled pulse of air, of a pre-determined pressure. First, the system design and alterations are described, then in a series of model experiments, the standardisation and characteristics of the air-pulse were examined. These studies revealed that the NCCA could produce a repeatable stimulus of known volume and rate of air-flow. Furthermore, the air-flow exiting the stimulus air jet was of a laminar shape, with minimal dispersion. The control of the air-flow dispersion was further enhanced by using a 0.5mm diameter air jet and a working distance of lcm. Varying the stimulus duration was not found to influence these qualities of the air-pulse. The air-pulse stimulus was shown to possess the ability to produce corneal nerve stimulation either by surface deformation, temperature change, or both. Using thermal imaging equipment, a temperature drop in the ocular tear film was demonstrated that was localised, and limited to the cornea. A second series of experiments investigated the ability of the NCCA to measure a corneal sensitivity threshold. These studies indicated that a forced-choice, doublestaircase, Method of Limits experimental technique produced an accurate threshold, with low variability in the results, over a minimum time period. Further studies showed that this threshold measurement was repeatable to within 0.1 mbars. A database of typical normal sensitivity thresholds, under a number of physiological variables - corneal location, gender, age and iris colour, was developed. The results from these studies compared well qualitatively with those using invasive stimuli. A third series of experiments examined the ability of the NCCA to assess corneal nerve function when it was under a number of external influences. The first situation was that of anaesthesia,p roduced by 0.4% benoxinate hydrochloride. Non-contact corneal sensitivity loss and recovery were shown to return to normal levels 60mins after instillation of the anaesthetic. The second situation was that of long-term contact lens wear (i.e. longer than three years). Non-contact sensitivity was shown to be reduced with both soft and gas-permeable lens wear, although the extent of loss did not differ between them, nor was it influenced by the length of wear. Thirdly,corneal sensitivity loss and recovery was assessed in subjects following excimer laser photorefractive keratectomy (PRK). Three laser trials were completed: a longitudinal myopic study, a transverse myopic study, and a longitudinal hyperopic study. The results indicated that non-contact corneal sensitivity loss/recovery was not related to the attempted depth of ablation, and that sensitivity had still not returned to normal levels one year post-op.

An investigation has been completed to determine the feasibility of using vibration measurement to develop an online tool wear monitoring system.Conventionaltransducers and FFT signal analysers have been used as the starting point for data collection and analysis. Additional software has been developed in order to obtain additional and enhanced analysis using statistical data such as percentile analysis and 4th statistical moments. The signal analysers have been interfaced with an IBM compatible PC to allow efficient data collection and analysis. • The measurement of surface finish via the use of centre line average has been selected as the primary indicator of tool wear. An experimental programme has been completed which examines the relationship between vibration measurement and surface finish during turning operations. This has provided sufficient general rules and guidelines to enable the method to be extended to other processes. It also provides information from which commonly occurring faults such as looseness of the tool holder, changes in material properties and swarf presence in the toolholder can be identified. Tests have been completed using cast iron, ENS and EN3 steels. An expert system has been developed. It has been demonstrated that sufficient data can be collected during the setting-up stage or commissioning part of a machining process from which, using the expert system, reliable tool wear monitoring can be achieved for all subsequent tests. In addition to predicting'the surface for all stages of tool life, the system can identify common faults such as looseness of the toolholder, the presence of swarf in the toolholder and changes in material properties. This system has been evaluated in relation to the available data, the present expectation of quality assesment required from the machine operation and relative to available commercial monitors. The system offers significant improvements.

No description available.

No description available.

Thesis (Ph.D.)--University of Western Australia, 2007.