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.

It is commonly known that coastal vegetation dissipates energy and aids in shoreline protection by damping incoming waves and depositing sediment in vegetated regions. However, this critical role of vegetation to dampen wave forces is not fully understood at present. A series of laboratory experiments were conducted in the Haynes Coastal Laboratory and 2-D flume at Texas A&M University to examine different vegetative scenarios and analyze the wave damping effects of incident wave height, stem density, wave period, plant type, and water depth with respect to stem length. In wetland regions vegetation is one of the main factors influencing hydraulic roughness. Traditional open-channel flow equations, including the Manning and Darcy- Weisbach friction factor approach, have been successfully applied to determine bottom friction coefficients for flows in the presence of vegetation. There have been numerous relationships derived relating the friction factor to different flow regime boundary layers to try and derive a wave friction factor for estimating energy dissipation due to bottom bed roughness. The boundary layer problem is fairly complex, and studies relating the wave friction factor to vegetation roughness elements are sparse. In this thesis the friction factor is being applied to estimate the energy dissipation under waves due to artificial vegetation. The friction factor is tuned to the laboratory experiments through the use of the numerical model COULWAVE so that the pipe flow formulation can be reasonably applied to wave problems. A numerical friction factor is found for each case through an iterative process and empirical relationships are derived relating the friction factor for submerged and emergent plant conditions to the Ursell number. These relationships can be used to reasonably estimate a wave friction factor for practical engineering purposes. This thesis quantitatively analyzes wave damping due to the effects of wave period, incident wave height, horizontal stem density, water depth relative to stem length, and plant type for a 6 m plant bed length. A friction factor is then determined numerically for each of the laboratory experiments, and a set of equations is derived for predicting a roughness coefficient for vegetation densities ranging between 97 stems/m2 and 162 stems/m2.

Skin is the largest organ of the human body. It is the first line of defense between the vulnerable organs and tissues of the body and the environment. Healthy skin is paramount to avoiding infection and disease. Therefore, any breach in the skin represents a significant risk to the health and comfort of its owner. Friction blisters are one of the most common modes of damage to human skin. In some extreme cases, such as those who suffer from Epidermal Bullosa, friction blisters are a very common and painful occurrence. Prior research on blister formation has been performed at mostly an observational level. In some cases, blisters have been deliberately created on human volunteers or animal test subjects. However, these studies are very difficult to recreate due to the legal issues of human and animal testing and the fact that no two people will have the same response to external stimulus. Other studies have followed athletes or soldiers who use different textile fabrics for socks or clothing to determine which have significant effects. Concurrent studies have focused on mimicking human skin for haptics research in product development. These have made great strides in introducing engineering properties such as coefficient of friction (COF) and elastic modulus into the field of skin study. While these studies are very useful to understanding the properties and mechanisms of human skin in rubbing applications, their primary audience is the cosmetics industry or product developers. There is a significant opportunity to take a similar approach of applying an engineering viewpoint to repeatably model the onset and formation of blisters on human skin. The authors have developed the Synthetic Skin Simulant Platform (3SP) to fulfill this role. The 3SP is a three-layer composite of elastomeric materials that outputs a visually recognizable blister upon sufficiently strong shear loading. The authors determined through two factorial experiments conducted on a custom wear testing table which variables were most significant to blister formation in the 3SP. The results showed that COF and dermal stiffness are the primary contributors. This agrees with prior literature about the significance of COF, and it suggests that dermal stiffness is a significant factor that merits examination in future blister research. Finally, the authors ran another experiment to ascertain the influence of textile fabrics and surface treatments on blister formation in the 3SP. The results demonstrated that surface treatments of corn starch and aloe-based lubricant were effective at mitigating blister formation on the 3SP. Furthermore, the results show that fabric is also bordering statistical significance on blistering.

This study calculate the frictional temperature of the dissimilar metal pair by theoretical analysis. Analyze the frictional temperature rise at interface dividing into the flash temperature rise and the bulk temperature rise. According the frictional temperature rise, establish the model of the temperature rise at the first cycle and the quasi-steady state cycle. And then discuss the condition of asperity contact by the measurement of experimental temperature rise. In the bulk temperature rise and the flash temperature rise, compare with the exact solution, the approximate solution of the average temperature rise that we derived have little error in specific range of Peclet number. Combine the approximate solution of the bulk temperature rise and the flash temperature rise to calculate the temperature rise of asperity contact at rubbing interface. We can evaluate the average contact length of asperity by measured values.

Nanoscaled-Al2O3 particles reinforced 1050 Aluminum composites by FSP were successfully fabricated in this study. The grain size of 1050 aluminum was obviously refined to about 0.5£gm by friction stir process(FSP), and there was a tendency that grain size decreased with increasing of Al2O3 content, where grain size of 0.84£gm was achieved with 24.7vol% of Al2O3. Nanoscaled-Al2O3 particles reinforced 1050 Al alloy by FSP revealed an excellent strengthening effect and excellent ductileity, Where hardness and UTS of the composite with 24.7vol% nanoscaled-Al2O3 particles were increased up to Hv113 and 310MPa respectively. The tensile result showed a 400% of increase in UTS comparing to the pure Al after FSP.

Automotive engine mounts are used to support engine weight, protect engine from road inputs and isolate transmission of vibrations created by the engine, which has a drastic effect on the noise generated inside the passenger cabin. Most common types of engine mounts are elastomeric and hydraulic mounts, the former having better vibration isolation characteristics whereas the latter displays better shock isolation. Elastomeric mounts are widely used for their low initial cost, while hydraulic mounts with inertia track and decoupler are chosen for their good vibration isolation and shock excitation characteristics. However, hydraulic mounts with inertia track and decoupler are not appropriate for small segment and commercial vehicles due their high initial cost. In this thesis, the effect of the addition of a dry friction damper on the performance of elastomeric automobile engine mounts is investigated. Friction dampers are used to attenuate vibration amplitudes in many applications such as gas turbine engines, railway vehicles, space structures and civil buildings. In this study, a friction element is added to the engine mount at its axial direction and its effect is studied. Results show that, the addition of dry friction damping to the original system increases vibration isolation performance significantly at low frequencies / whereas, due to the increased stiffness of the system, at high frequencies dry friction damper has a mitigating effect on performance. In order to overcome this problem, original system parameters are modified. In the modified system a softer mount that increase vibration isolation performance at high frequencies / but, which might cause excessive static deflection due to reduced stiffness of the system is used. On the other hand, addition of dry friction damping prevents excessive static deflections due to the increased stiffness effect and also increases the performance at high frequencies due to the soft mount. Final results showed that vibration isolation performance at low frequencies increases considerably while vibration isolation performance at high frequency is similar and even slightly better than the original system with addition of dry friction damping.

ABSTRACT Because of a great variety of tribocomponents and lubricants, the phenomenon of frictional magnetization and electrification between tribocomponents becomes more obvious. In order to understand the effects of frictional magnetization and electrification on tribology characteristics and miniature electrical control component signal, the frictional magnetization and electrification test under dry friction condition is investigated by the reciprocating electrification tester. Three material-pair types will be investigated their frictional magnetization and electrification behavior under various operating parameters, e.g. driver speed, normal load, and sliding distance. Moreover, the worn surface will be observed by the optical microscopy and SEM. Results show that the magnetization and electrification on friction surfaces increases with increasing load, and decreases with the carbon content of a material, and depends on material-pair. It is found that wear particles have been magnetized on the friction surface, even that the wear particles has been adhered to the surface caused by electro static action. Moreover, in the microscopic view, the frictional magnetization and electrification are related to both friction and wear.

Abstract Friction stir processing (FSP) is modified to produce various grain sizes of aluminum matrix composites (Al-Al2O3, Al-Zn-Al2O3 and Al-Zn) ranging from 300 nm to 3£gm. The microstructures of the composites were characterized using SEM and TEM. Tensile tests were performed to evaluate the mechanical properties of these composites. In the Al-Al2O3 system, it was found that the nano-scale alumina made it very effective to accumulate dislocations within grains during deformation, and resulted in increasing working hardening rate which is very critical to extend uniform elongation for materials with submicron grain sizes. In the Al-Zn-Al2O3 system, addition of Zn which dissolved into Al matrix to form solid solution and subsequently uniformly distributed G-P zones can improve strength and uniform ductility to some extent, comparing to those without addition of Zn. In addition, the relaxed and dislocation-free boundaries were observed regardless the existence of Al2O3 particles on boundaries. As a result, ko derived from Hall-Petch equation from various strain region decrease as Zn increases. In the Al-Zn system, experimental evidence suggests that increasing Zn content from 0 to 15wt% can enhance the total elongation but not uniform elongation as a result of the uniform spreading of the fine slip bands all over the gauge length and the contribution of grain boundary sliding (GBS) at RT. The relaxed and dislocation-free boundaries and GBS are attributed to the combination of high fraction of high-angle GBs and high GB diffusion to help fast dislocations annihilation at boundaries.

Thesis (M.S.)--Brigham Young University. Dept. of Mechanical Engineering, 2004. / Includes bibliographical references (p. 83-85).

Thesis (M.S.)--Brigham Young University. Dept. of Mechanical Engineering, 2004. / Includes bibliographical references (p. 27-40).