Failure in structural materials occurs initially by localization of deformation, and subsequently through a process of nucleation, growth and coalescence of voids. Predicting material failure requires a careful investigation of the different stages of damage evolution at the multiple scales. The main objective of this thesis is to explore the evolution of damage and to correlate this with the deformation of the material at the continuum and microstructural levels. This is accomplished through macroscopic measurements of strain evolution using digital image correlation and microscale measurements of strain and damage using optical and scanning electron microscopy. Three materials with different microstructure were examined. In oxygen-free, high-conductivity copper, a high-purity material without appreciable second phase particles, strain levels in the order of three were observed in the material without any trace of damage. Failure was observed to be triggered by plastic instability in the form of shear bands and the emergence of a prismatic cavity that grows in a self-similar fashion by an alternating slip mechanism. In Al 6061-T6, a material with a dispersion of second phase particles at a volume fraction of about 0.01, nucleation of damage does not appear until plastic strain levels of 0.5 to 1.0. Once damage in the form of particle fracture or decohesion at the interface initiates, subsequent failure follows by the void nucleation, growth and coalescence; but, dominated by the fluctuations in the distribution of second phase particles, final separation occurs in a highly localized layer of material on the order of the grain size, corresponding to a small increase in the overall strain. In nodular cast iron, a material with an initial porosity of about 0.10, growth of voids was observed initially, but this was terminated by a transition of the deformation into a localized region. Phenomenological models based on strain-to-failure and micromechanical models based on a mechanistic description of the microscale deformation are evaluated in light of the above examination of failure in these three classes of materials. / text

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ITC/USA 2010 Conference Proceedings / The Forty-Sixth Annual International Telemetering Conference and Technical Exhibition / October 25-28, 2010 / Town and Country Resort & Convention Center, San Diego, California / Most helicopter programs require the acquisition of parameters from the rotating systems. Historically, these systems made use of electromechanical slip rings for the transfer of power, control, and data from within the helicopter's cabin to the rotating hardware. Slip rings are primarily used in dedicated instrumentation vehicles and are not commonly used in production platforms that may require instrumentation of the rotating systems for in-service load and fatigue monitoring. Additionally, the use of slip rings requires time and money to integrate the hardware and equipment into the aircraft in order to perform rotor data acquisition. The time needed to perform modifications to transmissions and drive trains plays a big factor in the increased costs of aircraft development. Less intrusive installations would minimize the need for mechanical changes and would improve the time needed to install the instrumentation. This paper describes a wireless system approach to perform the test without the slip ring, and provides performance data that validates this new method of instrumenting unobtrusively to save time and money without sacrificing data integrity.

Poly(N-isopropylacrylamide) (PNIPAM) belongs to a class of stimuli-responsive materials known as “smart” polymers. When cast in the form of a hydrogel, PNIPAM’s lower critical solution temperature (LCST) of 32°C serves as a threshold for volumetric change. For solution temperatures below LCST, PNIPAM hydrogels exist as swollen, hydrophilic networks of polymer and water, spontaneously expelling the bound water molecules to shrink (and become increasingly hydrophobic) as temperature increases beyond LCST. This thesis centers on PNIPAM hydrogel layers grafted along the inner diameter of glass capillaries in order to form a temperature-responsive gating mechanism that spontaneously seals for solution temperatures below LCST. Surprisingly, very thin layers (10-20µm) of PNIPAM have dramatic effects on bulk fluid flow through the capillary due to complex interactions at the swelling interface. Specifically, for the case of capillary pressure driven flow, the swelling PNIPAM interface gives rise to "stick-and-slip" motion for bulk flow. Experiments explore the extent of this phenomenon, while a theoretical framework is proposed to model how the evolving gel interface pins the contact line. Additionally, an exploratory segment of this work examines the ways in which PNIPAM hydrogel nanoarrays can be synthesized via scalable template methods. Nanostructured PNIPAM films exhibit dramatic changes in surface properties with temperature, characterized by very low contact angles (~10°) below LCST, and very high ones (~160°) above LCST. Results for several methods are presented with lessons learned to guide future development of surfaces with temperature-responsive wetting properties.

The no-slip boundary condition is the foundation of traditional lubrication theory. It says that fluid adjacent to a solid boundary has zero velocity relative to that solid surface. For most practical applications the no-slip boundary condition is a good model for predicting fluid behavior. However, recent experimental research has found that for special engineered surfaces the no-slip boundary condition is not applicable. Measured velocity profiles suggest that slip is occurring at the interface. In the present study, it is found that judicious application of slip to a bearings surface can lead to improved bearing performance. The focus of this thesis is to analyze the effect an engineered slip/no-slip surface could have on hydrodynamic bearing performance. A heterogeneous pattern is applied to the bearing surface in which slip occurs in certain regions and is absent in others. Analysis is performed numerically for both plane pad slider bearings and journal bearings. The performance parameters evaluated for the bearings are load carrying capacity, side leakage rate and friction force. Fluid slip is assumed to occur according to the Navier relation and the effect of a critical value for slip onset is considered.

In today’s energy sector, it has been observed a revolutionary increase in shale gas recovery induced by reservoir fracking. So-called unconventional reservoirs became profitable after introducing a well stimulation technique. Some of the analysts expect that shale gas is going to expand worldwide energy supply. However, there is still a lack of an efficient as well as accurate modeling techniques, which can provide a good recovery and production estimates. Gas transports in shale reservoir is a complex process, consisting of slippage effect, gas diffusion along the wall, viscous flow due to the pressure gradient. Conventional industrial simulators are unable to model the flow as the flow doesn’t follow Darcy’s formulation. It is significant to build a unified model considering all given mechanisms for shale reservoir production study and analyze the importance of each mechanism in varied conditions. In this work, a unified mathematical model is proposed for shale gas reservoirs. The proposed model was build based on the dual porosity continuum media model; mass conservation equations for both matrix and fracture systems were build using the dusty gas model. In the matrix, gas desorption, Knudsen diffusion and viscous flow were taken into account. The model was also developed by implementing thermodynamic calculations to correct for the gas compressibility, or to obtain accurate treatment of the multicomponent gas. Previously, the model was built on the idealization of the gas, considering every molecule identical without any interaction. Moreover, the compositional variety of shale gas requires to consider impurities in the gas due to very high variety. Peng-Robinson equation of state was used to com- pute and correct for the gas density to pressure relation by solving the cubic equation to improve the model. The results show that considering the compressibility of the gas will noticeably increase gas production under given reservoir conditions and slow down the production decline curve. Therefore, for a more accurate prediction of shale gas production, it is crucial to consider compressibility behavior of the gas.

Thesis (M. Sc.)--University of Canterbury, 2004. / Typescript (photocopy). Includes transparent overlays. Includes bibliographical references (leaves 147-152). Also available via the World Wide Web.

Thesis (B.S.)--University of Missouri, School of Mines and Metallurgy, 1939. / The entire thesis text is included in file. Typescript. Title from title screen of thesis/dissertation PDF file (viewed April 26, 2010) Includes bibliographical references (p. 25).

Large earthquakes often exhibit complex slip distributions and occur along non-planar faults, resulting in variable stress changes throughout the fault region. To better discern the role of stress changes and fluid flow on aftershock sequences, we examine areas of enhanced and reduced mean stress along the structurally complex strike-slip faults that hosted the 1992 Landers, 2010 El-Mayor Cucapah, and 2016 Kumamoto earthquakes. We characterize the behavior of aftershock sequences with the Epidemic Type Aftershock-Sequence Model and use the Maximum Log Likelihood method to determine the optimal set of ETAS parameter values along each fault. This study indicates that extensional areas experience greater secondary aftershock triggering and a higher density of aftershocks directly following the mainshock, which could be attributed to fluid influx. However, our results also highlight some shortcomings of the ETAS model, including high parameter correlation, and influence of catalog size and magnitude cutoff on parameter estimations.

AN ABSTRACT OF THE THESIS OF Jacob Boone, for the Master of Science degree in Mechanical Engineering, presented on 10/28/2010, at Southern Illinois University Carbondale. TITLE: DESIGN, CONSTRUCTION, AND EVALUTAION OF UNIVERSAL FRICTION TESTER MAJOR PROFESSOR: Dr. Peter Filip Many different types of friction testers are currently available for testing specific frictional applications. Of these machines very few have versatility, and of the ones that do, the amount of versatility is limited. Since friction is a property specific to each system, all operating parameters need to match the specific application as closely as possible in order to obtain accurate data. This requires many research facilities to have several specific friction testers in order to provide the necessary testing capabilities. The goal of this project was to design a Universal Friction Tester (UFT) with enough versatility to reproduce most types of sliding friction situations. This was accomplished by providing a wide range of testing capabilities through the use of interchangeable system components. Results show that the UFT provides quality data over its entire operating range. It was shown that normal pressure, sliding speed, temperature and system stiffness all have drastic effects on frictional performance. By using a borosilicate glass disc, the friction surface was viewed in-situ during testing. This allowed insights into true surface temperature and contact area. In conclusion, the UFT can successfully take the place of several friction testers and thus provide many friction research capabilities while requiring fewer resources. The wide range of testing capabilities will allow the UFT to be used as a research tool for many types of advanced friction studies. Some of these may include true surface temperatures, true contact area, influence of conditions on stick-slip phenomenon, and thermo-elastic instabilities.