No description available.

A considerable number of total-joint replacement devices used in orthopedic medicine involve articulation between a metallic alloy and ultra-high molecular weight polyethylene (UHMWPE). Though this polymer has excellent wear resistance, the wear particulate produced leads to the limited lifetime of the devices – osteolytic bone loss. Crosslinking has been shown to reduce the wear rate of UHMWPE, but can cause a reduction in various mechanical properties such as impact toughness. This study presents two alternate approaches to improving the wear performance of UHMWPE in orthopedic applications Previous work has shown that UHMWPE-based composites have wear resistance comparable to the irradiation-crosslinked polymer. Zirconium has been shown to have excellent corrosion resistance and biocompatibility, and the authors have used the material as reinforcing filler in UHMWPE with promising results. Compression-molded UHMWPE composites with up to 20 weight percent (wt%) of micro-sized zirconium particles were investigated with regards to wear behavior and impact toughness. These composites showed a significant reduction in wear compared to unfilled polymer while still maintaining impact toughness. These results reinforce the paradigm of using polymer composites for orthopedic applications and may provide a viable alternative to the property tradeoffs encountered with irradiation crosslinking. Apart from UHMWPE, novel materials including hydrogels and bio-derived polymers show great potential in orthopedics, but such materials require the development of innovative fixation techniques [1-3]. The development of controlled porous UHMWPE morphologies offers the opportunity to utilize and expand these developing technologies. Interconnected porous structures were prepared by dry mechanical mixing of NaCl particles and UHMWPE powders followed by compression molding. Samples were soaked in water to remove the embedded salt, leaving a porous UHMWPE structure. Computational simulations of porogen distribution and leaching predicted leaching to be 95% effective when initial salt concentrations were 60wt% and higher, which was found to match very well with the experimental data. It was found that varying the concentration and particle size of the porogen can tailor the final pore morphology to a specific application, while DMA results showed that storage and loss moduli depend greatly on porosity, but not on pore size. Finally, porous UHMWPE scaffolds were successfully impregnated with gelatin, confirming the compatibility of UHMWPE with hydrogel-based fillers.

Prehistoric quarries in America are poorly understood and thus problematical to take into account when making inferences about past behavior. A microwear analysis of Clovis blades from the 2000 Texas A&M University excavations at the Gault site (41BL323), located in southern Bell County, Texas, provided a window into this problem. Texas A&M excavations on the site produced an extraordinarily large number of Clovis artifacts in two bounded geologic units, 3a and 3b. Included in the artifact types are blades, specialized elongate flakes associated with a core and blade technology. In conducting a microwear analysis of the Clovis blades from Gault, I proposed the following questions: (1) were the Clovis blades utilized at Gault?; (2) is there a difference in the use-wear patterns of Clovis blades from the geological units 3a and 3b?; and (3) is Gault, as a quarry/workshop site, a place to just obtain raw materials or did it also serve as a craft site? Observations from experiments, stereomicroscope analysis, compound microscope analysis, and SEM/EDS analysis led to answers for two research questions: (1) blades were used at Gault and (2) there is a difference between Clovis units 3a and 3b. Eight Clovis 3a blades, or 3.0% of the total Clovis 3a blade/blade fragment population (n=264), exhibit use-wear. Six Clovis 3b blades, 3.3% of the total Clovis 3b blade/blade fragment population (n=182), exhibit use-wear. In general, Clovis 3b blades were used on harder contact materials (wood to bone) than those in Clovis Unit 3a (softer contact materials similar to grass, sinew, and rawhide). The function(s) of quarries and quarry-related workshops were interpreted by William Henry Holmes as a place to obtain raw materials, while Kirk Bryan interpreted them as a place to bring other materials to work in craft activities. Following the microwear analysis of Clovis blades/blade fragments at Gault, I compared Gault to three other Paleoindian quarry-workshop sites (Wells Creek, Dutchess Quarry, and West Athens Hill). My intent is to provide supplemental data for the consideration when applying Holmes’ and Bryan’s respective hypotheses.

Traditionally, there are several kinds of method for restraining wear. Usually, it includes the choice of the best operating conditions, the surface coating, the surface heat treatment, and the choice of the best lubricants. Among these methods, only the choice of the best lubricants has the mendable process of chemical element for worn surface, others do not have the mendable process. Consequently, this project proposes a method of continuous tribo-plating, and takes preliminary experiments by using SUJ2 ball specimen and S45C disk specimen to investigate the effects of rotational speed, anode¡¦s density of current, and specimen¡¦s surface roughness on the coating growing rate and the coefficient of friction. Results show that the coating growing rate increases with increasing rotational speed and anode¡¦s density of current, but it doesn¡¦t be influenced by surface roughness. According to the experimental results, it is found that the frictional coefficient in order is uncoated specimen, coated specimen, and continuous coated specimen. Furthermore, at continuous tribo-plating test, specimen whose surface roughness is rough has lower frictional coefficient. According to the analyses of surface pattern and composition, specimen whose surface roughness is rough remains a lot of piece-like coating film on the surface, and this residual film provides a good effect of lubrication. The result of this project proves that continuous tribo-plating not only reduces frictional loss but also has the mendable process of worn surface.

With the development of MEMS and nano-technology, effects of tribo-electrification on the size accuracy and quality of micro-element will be more sensitive. The electrification in the order of mV is also important in the nano-machining process. Therefore, the tribo-electrification mechanisms and characteristics between the metal surfaces are investigated in this study. The experiments are conducted on a reciprocating friction tester with a measuring system, and the tribo-electrification behavior is studied for eleven pure metals, namely, Platinum (Pt), Ferrous (Fe), Molybdenum (Mo), Titanium (Ti), Tungsten (W) and Lead (Pb), Zinc (Zn), Aluminum (Al), Silver (Ag), Aurum (Au), Copper (Cu), in dry severe wear process. According to the SEM and EDS observations on the wear particles and the worn surfaces, the tribo-electrification mechanisms between the metal surfaces are proposed. Concerning the study of self-mated pure metal pairs; a model of the tribo-electrification mechanism by asperity removal for five hard metal pairs of Pt/Pt, Fe/Fe, Mo/Mo, Ti/Ti, and W/W is proposed. In this model, the wear for the hard self-mated metals is mainly caused by the asperity removal with small wear particle. When the material transfers from pin specimen to plate specimen, the polarity of tribo-electrification for pin specimen becomes positive, and vice versa. Another model of the tribo-electrification mechanism by junction growth for six soft metal pairs of Pb/Pb, Zn/Zn, Al/Al, Ag/Ag, Au/Au and Cu/Cu is proposed. In this model, the wear mechanism of the soft self-mated metals is the flake-like wear particles that are formed by the particle aggregation with junction growth. The polarity of tribo-electrification for the upper specimen keeps negative due to the wear loss of the upper specimen always less than the plate specimen. Furthermore, the transition mechanisms of tribo-electrification are investigated with changing normal load, hence a map has been established to predict the polarity of tribo-electrification for self-mated metal pairs. That is, with increasing normal load, the polarity of tribo-electrification varies from the random, through tending to negative, to negative, and the formation mechanism of wear particle from the micro-asperity removal, through the transition, to the particle aggregation with junction growth. Moreover, an equation is proposed to predict the average magnitude of tribo-electrification. Results show that the average magnitude of electrification voltage is linearly proportional to the electric resistivity and the relative wear rate, but inversely to the real contact area. Concerning the study of dissimilar metal pairs of Pb/Fe, Ag/Fe, Cu/Fe, Zn/Fe and Al/Fe; the total voltage of tribo-electrification Vt for dissimilar metal pairs consists of three components: (a) tribo-electrification by material transfer Vw, Vw is independent of the reciprocating speed, and is proportional to the (1+n) power of normal load, where n is in the range from ¡V0.5 to ¡V0.9 for lead, silver, copper, zinc, and aluminum. (b) tribo-electrification by friction heat Vf, Vf is linearly proportional to the reciprocating speed, and is proportional to the square root of normal load. (c) tribo-electrification by residual heat Vr, Vr is linearly proportional to the reciprocating speed, and is proportional to the square root of normal load. Moreover, Temperature rise Tt between the contact surfaces can be calculated by Vf and Vr. Hence, Tt consists of two components: (a) temperature rise by friction heat Tf, an equation is proposed to predict Tf. Results show that Tf is a function of friction coefficient, normal load and speed. (b) temperature rise by residual heat Tr, Tr is linearly proportional to the reciprocating speed, and is proportional to the square root of normal load. Finally, a model of tribo-electrification mechanism for dissimilar metal pairs is proposed to describe the tribo-electrification phenomenon for sliding pairs with low to high mutual solubility.

The labyrinth seal is widely used in turbomachinery to minimize or control leakage between areas of different pressure. The present investigation numerically explored the effect of damage and wear of the labyrinth seal on the turbomachinery flow and temperature fields. Specifically, this work investigated: (1) the effect of rubgroove downstream wall angle on seal leakage, (2) the effect of tooth bending damage on the leakage, (3) the effect of tooth "€œmushrooming"€ damage on seal leakage, and (4) the effect of rub-groove axial position and wall angle on gas turbine ingress heating. To facilitate grid generation, an unstructured grid generator named OpenCFD was also developed. The grid generator is written in C++ and generates hybrid grids consisting primarily of Cartesian cells. This investigation of labyrinth seal damage and wear was conducted using the Reynolds averaged Navier-Stokes equations (RANS) to simulate the flows. The high- Reynolds k - Model and the standard wall function were used to model the turbulence. STAR-CD was used to solve the equations, and the grids were generated using the new code OpenCFD. It was found that the damage and wear of the labyrinth seal have a significant effect on the leakage and temperature field, as well as on the flow pattern. The leakage increases significantly faster than the operating clearance increase from the wear. Further, the specific seal configuration resulting from the damage and wear was found to be important. For example, for pure-bending cases, it was found that the bending curvature and the percentage of tooth length that is bent are important, and that the mushroom radius and tooth bending are important for the mushrooming damage cases. When an abradable labyrinth seal was applied to a very large gas turbine wheelspace cavity, it was found that the rub-groove axial position, and to a smaller degree, rub-groove wall angle, alter the magnitude and distribution of the fluid temperature.

<p>A general approach to numerically simulating wear in rollingand sliding contacts is presented in this thesis. A simulationscheme is developed that calculates the wear at a detailedlevel. The removal of material follows Archard’s wear law,which states that the reduction of volume is linearlyproportional to the sliding distance, the normal load and thewear coefficient. The target application is the wheel-railcontact.</p><p>Careful attention is paid to stress properties in the normaldirection of the contact. A Winkler method is used to calculatethe normal pressure. The model is calibrated either withresults from Finite Element simulations (which can include aplastic material model) or a linear-elastic contact model. Thetangential tractions and the sliding distances are calculatedusing a method that incorporates the effect of rigid bodymotion and tangential deformations in the contact zone.Kalker’s Fastsim code is used to validate the tangentialcalculation method. Results of three different sorts ofexperiments (full-scale, pin-on-disc and disc-on-disc) wereused to establish the wear and friction coefficients underdifferent operating conditions.</p><p>The experimental results show that the sliding velocity andcontact pressure in the contact situation strongly influencethe wear coefficient. For the disc-on-disc simulation, therewas good agreement between experimental results and thesimulation in terms of wear and rolling friction underdifferent operating conditions. Good agreement was alsoobtained in regard to form change of the rollers. In thefull-scale simulations, a two-point contact was analysed wherethe differences between the contacts on rail-head to wheeltread and rail edge to wheel flange can be attributed primarilyto the relative velocity differences in regard to bothmagnitude and direction. Good qualitative agreement was foundbetween the simulated wear rate and the full-scale test resultsat different contact conditions.</p><p><b>Keywords:</b>railway rail, disc-on-disc, pin-on-disc,Archard, wear simulation, Winkler, rolling, sliding</p>

Thesis (Ph.D.)--University of Wollongong, 2009. / Typescript. Includes bibliographical references: p. 267-287.

Thesis (M.S.)--West Virginia University, 2001. / Title from document title page. Document formatted into pages; contains xiv, 160 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 120-122).

Thesis (Ph. D.)--Ohio State University, 2004. / Title from first page of PDF file. Document formatted into pages; contains xxviii, 254 p.; also includes graphics. Includes abstract and vita. Advisor: Taylan Altan, Dept. of Industrial and Systems Engineering. Includes bibliographical references (p. 240-248).