Mode of access: World Wide Web. / Thesis (Ph. D.)--University of Hawaii at Manoa, 2005. / Includes bibliographical references (leaves 94-111). / Electronic reproduction. / Also available by subscription via World Wide Web / xv, 111 leaves, bound ill. (some col.) 29 cm

Thesis (Ph. D.)--University of Wisconsin--Madison, 1955. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

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With the development of urban areas and the constant need to change or improve the existing structures, a need for creative and less destructive soil reinforcement processes has occurred. Jet-grouting is one possible ground improvement technique. The behavior of the soil improved by jet-grouting is still not well understood. In this thesis, the mechanical behavior of the injected soil is modeled in order to determine the different parameters needed for the engineering design of a soil reinforcement based on jet-grouting. At first several models are presented in order to determine the extent of the injected zone within the soil mass, based on engineering parameters (cement poroelastic properties, injection rate). A model based on an energetic balance is proposed to compute the lower bound of the injection radius. The second part of the thesis focuses on the characterization of the uniaxial compressive strength of the soilcrete created in the injected area determined in the first part. Three different methods have been adapted to the problem. A hollow sphere model has been calibrated against published data. After calibration, both Eshelby's and averaging methods proved to provide results close to the reference data. The last part of this report presents numerical studies of the pile and of a group of piles. The study of the group of piles focuses on the effect of arching between soilcrete columns to reduce the vertical settlements due to urban tunneling at the surface. It appears that the values obtained for settlements in the presence of jet-grouted columns are much less important than in usual tunneling problems (with no reinforcement).

The demand for renewable load-carrying materials is increasing with increasing environmental awareness. Alternative sources for materials manufacturing and design have to be investigated in order to replace the non-biodegradable materials. The work presented in this thesis investigates structure-property relations of such renewable materials based on cellulose nanofibrils. Cellulose is the most abundant polymer on earth and exists in both ordered and disordered phases, where the ordered crystalline cellulose shows excellent mechanical properties. The celluloses nanofibril is composed of partly crystalline cellulose where the stiff crystal regions, or crystallites, are orientated in the axial direction of the fibrils. The cellulose nanofibrils have a high aspect ratio, i.e. length to diameter ratio, with a diameter of less than 100 nm and a length of some micrometres. In the presented work, different properties of the cellulose nanofibril were studied, e.g. elastic properties, structure, and its potential as a reinforcement constituent. The properties and behaviour of the fibrils were studied with respect to different length scales, from the internal structure of the cellulose nanofibril, based on molecular dynamic simulations, to the macroscopic properties of cellulose nanofibril based materials. Films and composite materials with in-plane randomly oriented fibrils were produced. Properties of the cellulose nanofibril based materials, such as stiffness, thickness variation, and fibril orientation distribution, were investigated, from which the effective elastic properties of the fibrils were determined. The studies showed that a typical softwood based cellulose nanofibril has an axial stiffness of around 65 GPa. The properties of the cellulose nanofibril based materials are highly affected by the dispersion and orientation of the fibrils. To use the full potential of the stiff fibrils, well dispersed and oriented fibrils are essential. The orientation distribution of fibrils in hydrogels subjected to a strain was therefore investigated. The study showed that the cellulose nanofibrils have high ability to align, where the alignment increased with increased applied strain.

Many concentrated paste-like materials are composed of deformable particles randomly packed into a dense suspension. Examples of the constituent soft particles include polyelectrolyte microgels, emulsion droplets, polymer coated colloids, and star polymers. These materials share in common many properties such as yield stress, shear thinning, non-zero normal stresses, wall-slip, shear-banding, memory and aging (similar to that in structural, spin and polymer glasses). Their unique properties make soft particle pastes (SPPs) scientifically interesting and extremely useful in industrial applications (as rheological modifiers). In this dissertation particle simulations, theoretical models and experiments are used to study the flow dynamics and rheological behavior of SPPs near confining surfaces - wall-slip and shear flow, and in the bulk - elasticity at small stresses and the non-linear shear rheology. In the study of slip near smooth surfaces, rheological measurements are shown that identify the influence of the chemical nature of the shearing boundary on slip at the shearing boundary. A modified elastohydrodynamic model is presented that incorporates attractive and repulsive short range interactions between the paste particles and captures the corresponding suppression and promotion of slip at the wall. Further, fluorescence microscopy and particle tracking velocimetry is used to visualize slip and flow of pastes near smooth boundaries and study the sensitivity of the bulk flow profile to the nature of the shearing surface. In the study of elastic properties of pastes, SPPs are modeled as three-dimensional systems of randomly packed elastic spheres. Simulations are performed wherein the packing is subject to small deformations to compute the high- and low-frequency shear moduli. The simulation results are compared with the data from experiments on microgel pastes. This model is extended to study paste dynamics under simple shear with added pairwise elastohydrodynamic lubrication interactions between the densely packed soft particles. The shear and normal stress differences generated during simple hear flow are calculated that compare well with the experimental data. In addition, the pair distribution function of the initial isotropic configuration, the elastically deformed and the steady sheared configurations is investigated. A semi-empirical analysis of the microstructure and its evolution due to shearing is presented. / text

Two-dimensional (2D) transition metal dichalcogenides (TMDs) with intrinsic band gaps are considered to be prospective alternatives for graphene in the applications of emerging nano-semiconductor devices. As a significant member of the TMDs family, WSe₂ with superior optical properties attracts increasing attention, especially in the optoelectronics. In this thesis, the electronic and mechanical properties of 2D WSe₂ have been studied experimentally and theoretically. Firstly, the fabrication of substrate-supported and suspended pre-patterned WSe₂ FETs with the low-cost optical lithography and vapour HF etching technology have been realised. The subsequent electrical measurement of the fabricated WSe₂ FETs indicates that the WSe₂/dielectric interface can affect the electrical performance of 2D WSe₂ negatively. To gain more insights on the impact of field-effect on 2D WSe₂, first-principle calculations have been conducted in this research to study the evolutions of the crystal structure, electronic band structure, conductive channel size, and electrical transport property of WSe2 under various levels of field-effect. Furthermore, a layer thinning and chemical doping method of 2D WSe₂ by vapour XeF₂ exposure featured with good air-stability, scalability, and controllability has been developed to enable the layer engineering of 2D WSe₂ and integration of 2D WSe₂ to logic circuits, solar cells, and light-emitting diodes (LED). The thinning and doping mechanism has been investigated with a combination of Raman spectroscopy, photoluminescence (PL) spectroscopy, and Xray photoelectron spectroscopy (XPS) characterization techniques. Afterwards, the inplane elastic properties (including the Young's modulus, breaking strain, and etc.) of 2D WSe₂ have been measured with nanoindentation experiments implemented by atomic force microscopy (AFM). The results prove the suitability of 2D WSe₂ in the applications of flexible devices and nanoelectromechanical systems (NEMS) operating in the audio resonance frequency, such as acoustic sensors and loudspeakers. To provide a comprehensive understanding of the strain engineering of 2D WSe₂, the strain induced variations of the crystal structure, electronic band structure, and electrical transport property of 2D WSe₂ have been further studied with first-principle calculations, which paves the way for the performance tuning of 2D WSe₂ devices via strain and applications of 2D WSe₂ in strain sensors.

The fact that many of the giant hydrocarbon reservoirs, such as the Ghawar field in Saudi Arabia and the Grosmont formation in Alberta, are formed from carbonates make these rocks important research topics. Compressional and shear wave velocities (at 1 MHz) and the quasi-static strains of thirty seven carbonate rock samples were measured as functions of saturating fluid and confining pressure. Furthermore, P- and S-wave velocities of the saturated samples were measured at constant differential pressure of 15 MPa. The quasi-static strains of the samples under jacketed and unjacketed conditions were also simultaneously acquired. The lithology, mineralogy, porosity and pore type and size distribution of each sample were obtained using a combination of thinsection and scanning electron microscopy, helium porosimetry and mercury intrusion porosimetry. Due to the lack of closing microcracks and compliant pores in low porosity samples, the travel times show slight changes with the confining pressure. Whereas the high porosity samples show remarkable reduction of travel time with the increase of confining pressure in both P- and S-wave. The samples show no changes in travel time with increasing confining pressure under constant differential pressure, and this behavior is taken to be representative of full saturation of the sample and hence used as a measure of quality control. The comparisons of Biot, Gassmann, squirt-Biot and squirt-Gassmann model predictions with the measured water saturated velocities show that the squirt mechanism is not active on all the studied samples. Biot mechanism is likely to be the principle dispersion mechanism in these samples. For S-wave velocities, Gassmanns model consistently over-predict the saturated at low pressure and closely fit the measured velocities at high pressure, whereas, Biot model over-predicts the saturated velocities in most of the studied samples. The strains over the horizontal axis are higher than the vertical axis suggesting that the majority of the compliant pores and crack-like pores are oriented almost in direction parallel to the length of the sample. The static bulk modulus is always lower than dynamic one for all measured samples. The measured grain bulk modulus is reasonably close to the bulk modulus of the constituent mineral. / Geophysics

The purpose of this diploma project has been to investigate the elastic properties of hexagonal close-packed Fe-Ni-Mg alloys at high pressure. Recent research has suggested that iron and magnesium can form an alloy under high pressure because of the great compressibility of the magnesium atoms. This also makes it possible for magnesium alloying with nickel atoms which are very similar to iron so that we get Fe-Ni-Mg alloys. Learning more about the elastic properties of iron alloys at high pressure will give us a better understanding of the inner core of our planet, which is believed to be composed primarily of iron. The calculations are based on a ab-inito method supported on the Density Functional Theory. The calculations were performed with a simulation package based on the Exact Muffin-Tin Orbitals theory, in conjuction with the Coherent Potential Approximation. The effects that small impurities can have on iron are remarkable.

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