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Magnetoelastic coupling and relaxation processes in magnetic materials monitored by resonant ultrasound spectroscopyThomson, Richard Ian January 2013 (has links)
No description available.
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Moving object counting with an ultrasound sensor network /Gao, Min. January 2005 (has links)
Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2005. / Includes bibliographical references (leaves 58-60). Also available in electronic version.
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HIGH RESOLUTION ULTRASOUND SPECTROSCOPIC ANALYSIS OF BOVINE MUSCLETimothy Sweet Unknown Date (has links)
Accurate and reliable measurement of meat quality is essential for the Australian beef industry to remain competitive in both the domestic and export markets. Recent developments of the resonator technique have lead to the commercial availability of the High Resolution Ultrasound Spectroscope (HR-US). This research project was designed to assess the potential of HR-US for the analysis of post-mortem bovine muscle. This was accomplished by; 1) establishing a suitable measurement protocol that considered sources of variability, 2) the effects of post-mortem aging on HR-US parameters, 3) analysis of thermal related changes that occur in muscle, and extracted connective tissue during heating, and 4) the use of HR-US for the measurement of the intramuscular fat. A procedure for the measurement of bovine muscle with HR-US was established. Briefly, an external semisolid cell was used as the measurement cell. The frequency range of 2000 KHz to 3000 KHz was selected as the most suitable for whole muscle analysis and all five resonance peaks within this range were analysed and used to obtain velocity and attenuation values of the meat sample. Water was used as the reference media, and measurements were conducted at 250C. Changes were made to this method during experimental work depending on the sample being run and the objectives of the study. The measurement protocol was shown to be repeatable. Factors likely to cause variation in measurements of the samples, such as water loss and freeze-thaw, were also considered when developing the operational parameters of the study. High resolution ultrasound spectroscopy was applied to measure the post-mortem changes that occur in bovine muscle. Using two muscle types, Semitendinosus and Psoas major, significant changes were observed in HR-US parameters with ageing. Significant increases in the acoustic impedance of bovine muscle with increased ageing time were attributed to degradation of the muscle structure. This was confirmed in transmission electron microscopy images where clear disruption the myofibillar structure was apparent in the muscle at 21 days post-mortem.In localised regions the Z bands and the adjoining actin fibres were totally degraded. Water loss from the muscle system had a significant influence on HR-US measurements. Thermal related changes that occur in whole bovine muscle and in isolated intramuscular connective tissue were observed with HR-US. Heat induced changes were identified in whole muscles and included the melting of the fat within samples at 48oC, coagulation of sarcoplasmic proteins between 450C and 55oC, and the shrinkage of collagen fibres at 630C. An 80% reduction in the attenuating properties of extracted connective ageing in buffer solution was observed within the first 5 days. This is attributed to the degradation of proteoglycans and the resulting disassociation of collagen fibrils. Structural changes occurring in extracted connective tissue were observed with TEM. HR-US measurements proved to be highly sensitive to identifying temperatures at which transitions occurred. Unfolding of the triple helix structure of collagen was identified in velocity transitions between 59°C and 63oC. HR-US results suggested a greater sensitivity to thermal related changes in extracted intramuscular connective tissue when compared with differential scanning calorimeter results. An increase in temperature was observed for thermal denaturation of collagen with ageing, however a reduction was also observed in the temperature range at which the denaturation process occurred. Temperature ramps conducted on extracted intramuscular bovine showed a reduction in velocity from 1613.1m/s at 250C to 1343.1 m/s at 900C equalling an overall reduction in velocity of 270m/s. A transition in the velocity trend seen at 46°C indicates the majority of the triglycerides are melted (or in liquid state) above this temperature. Results are confirmed with differential scanning calorimeter thermogram. HR-US measurements showed high sensitivity to increasing concentration of bovine fat in prepared emulsions with an adjusted R2 99.46% for velocity measurements taken at 5100 kHz. Attenuation values at 8100 kHz also showed a strong linear response to increasing fat concentration in the emulsion (R2 98.77). The use of HR-US for the measurement of intramuscular bovine fat demonstrated a high sensitivity to extracted bovine fat in prepared emulsions. An increase in the intramuscular fat content of whole bovine muscles resulted in a reduction in the velocity measurements and an increase in the attenuation of the ultrasonic signal. This provides the basis for potential method for the prediction intramuscular fat in bovine muscle. The present studies have highlighted the complexities of investigations relating to meat quality and have demonstrated the diversity of data required to assess quality. Only when comprehensive data are available, can we hope to accurately determine meat quality and predict how it will vary with changes in animal production and meat processing.
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Ultrasonically controlled antibiotic release from hydrogel coatings for biofilm preventionNorris, Patrick Michael. January 2004 (has links) (PDF)
Thesis (M.S.)--Montana State University--Bozeman, 2004. / Typescript. Chairperson, Graduate Committee: Aleksandra Vinogradov. Includes bibliographical references (leaves 83-90).
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A resonant ultrasound spectroscopy study of hydrogen-absorbing intermetallic compoundsAtteberry, Jennifer Eve. January 2004 (has links)
Thesis (Ph. D.)--Colorado State University, 2004. / Includes bibliographical references.
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Elastic Properties of Bulk-metallic Glasses Studied by Resonant Ultrasound SpectroscopyZhang, Zhiying 01 August 2008 (has links)
The elastic properties of a solid are of considerable interest to both science and technology. Not only do they contain fundamental information about the nature of the inter-atomic bonding in the material, but they also determine the mechanical behavior of solids. In the past few years, considerable effort has been devoted to the study of elastic properties of bulk metallic glasses (BMGs), a relatively new class of metallic materials that display a unique combination of mechanical and physical properties. Our research has focused on Zr-based, Cu-based and Ca-based metallic glasses. Zr-based BMGs are known to have superior glass forming ability and high strength, but their ductility is too low for wide-spread practical applications. Cu-based BMGs recently received wide interest because of their low cost and good mechanical properties. Ca-based BMGs have low glass transition temperature Tg, around 390 K, which make them very attractive to be studied near Tg.
In this work, resonant ultrasound spectroscopy (RUS) has been applied to study the elastic properties of above mentioned BMGs from 5 K to their glass transition temperature Tg. RUS is a novel technique for determining the elastic moduli of solids, based on the measurement of the resonances of a freely vibrating body. In an RUS experiment, the mechanical resonances of a freely vibrating solid of known shape are measured, and an iteration procedure is used to “match” the measured lines with the calculated spectrum. This allows determination of all elastic constant of the solid from a single frequency scan.
Below Tg, the elastic constants of the BMGs under investigation show “normal” behavior, i.e. with increasing temperature, all moduli decrease and Poisson ratio increases. Above Tg changes in the trends occur due to structural relaxation and crystallization. We confirmed the suggested link between ductility and Poisson ratio: BMGs showing good ductility display high Poisson ratio. By increasing palladium content in Zr50Cu40-xAl10Pdx alloys, BMGs with high Poisson ratio and thus good ductility have been obtained. In addition, we developed a simple model to provide fast and good estimate of the temperature dependence of elastic constants of BMGs from room temperature measurements.
Keywords: Elastic properties; Bulk metallic glasses (BMGs); Resonant ultrasound spectroscopy (RUS); Internal friction.
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Elastic properties of complex transition metal oxides studied by Resonant Ultrasound SpectroscopyLuan, Yanbing 01 May 2011 (has links)
The elastic properties of novel transition metal oxides have been investigated, using a powerful technique known as Resonant Ultrasound Spectroscopy (RUS). Two sets of transition metal oxides have been studied. One is the ruthenate Ca2-xSrxRuO4 series with a layered perovskite structure, a Mott transition system that connects the Mott insulator Ca2RuO4 with the unconventional superconductor Sr2RuO4. The other set contains geometrically frustrated materials, including vanadium spinels AV2O4 (A = Zn, Mn and Fe) and titanate pyrochlores A2Ti2O7 (A= Y, Tb, Yb, Ho and Dy).
The elastic response of five Ca2-xSrxRuO4 single crystals (x = 2.0, 1.9, 0.5, 0.3 and 0.2) has been measured. For 2.0 ≥ x ≥ 0.5, a dramatic softening over a wide temperature range is observed upon cooling, caused by the rotational instability of RuO6 octahedra (for x = 2.0 and 1.9) or the static rotation of the octahedra (for x = 0.5). For the Ca-rich samples (x = 0.3 and 0.2), the softening occurs in a very narrow temperature range, corresponding to the structural phase transition from high-temperature-tetragonal to low-temperature-orthorhombic symmetry.
Elastic softening in ZnV2O4 is observed near the cubic-to-tetragonal structural phase transition at 50 K. The elastic response of MnV2O4 is quite unusual, displaying a softening over a wide temperature range with decreasing temperature. Upon cooling, C’ of FeV2O4 becomes so soft that it drops to almost zero around 140 K, where the cubic-to-tetragonal structural transition occurs.
For Y2Ti2O7, all three elastic constants show normal “Varshni” behavior. For spin liquid Tb2Ti2O7, all three elastic constants show a pronounced softening below 50 K, indicative of a possible Jahn-Teller, cubic-to-tetragonal transition at very low temperatures. It is also found that the application of a magnetic field suppresses the elastic softening in this compound. Another spin liquid Yb2Ti2O7 shows no elastic softening. The elastic moduli of the spin-ice compounds, Ho2Ti2O7 and Dy2Ti2O7, show a broad “dip” around 100 K, which is believed to be caused by the strong crystal field effect in those two compounds.
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High-temperature superconductivity in a family of iron pnictide materialsGillett, Jack January 2011 (has links)
The work in this thesis falls roughly into three parts, which I characterise loosely as a developmental stage, an exploratory stage, and an attempt to contribute to understanding of the field. In the developmental stage, I have worked to design a variety of methods to create high-quality samples of various Iron Pnictide superconductors, to dope them with various chemicals and to characterise the resulting crystalline samples. I discuss in depth the signature of good quality crystals and the various experiments that they have been used in by myself and my collaborators. These processes are ongoing and will hopefully continue to contribute to my research group's capabilities. My exploratory work involves a detailed survey of one particular family, Sr(Fe1-xCox)2As2, as the level of Cobalt is varied, and the mapping of the phase diagram for the system. I have also made a comparison to the better-measured Barium analogue, and discuss the reasons for the differences in character between the two, most notably the lack of a splitting of the structural and magnetic transitions in the first species. I also discuss the effect of pressure, which can lead to superconductivity in lightly doped samples for very modest pressures; and annealing, which increases transition temperatures within samples, on a limited quantity of crystals. Finally, I attempt to contribute to the understanding of the field via a series of Resonant Ultrasound Spectroscopic experiments conducted by a collaborator on my crystals and analysed by me. I see distinct first-order transitions in the parent compounds, characterisable above the high-T structural transition within a Ginzburg-Landau pseudoproper ferroelastic scheme for a transition coupling weakly to strain but driven by another order parameter. My observations allow several statements about the symmetry of the order parameter and are suggestive of a non-magnetically driven structural transition. In the case of doped samples a much richer behavior is seen, with a broad transition and simultaneous relaxation of all elastic peaks and a broad temperature range of significant dispersion. The effect of the softening is seen far above TN and lends strong support to the family of models predicting such high-T fluctuations.
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Residual stress hole drilling of elastic anisotropic commercially pure titaniumSanchez Archuleta, Zachary J. 28 May 2024 (has links)
Residual stress measurement methods have commonly been used to characterize states of stress in various elastic isotropic materials. In order to investigate the effects of elastic anisotropy on residual stress measurements, commercially pure grade 2 titanium (CP Ti Gr 2) was selected to study a strong texture, or preferred grain orientation. Warm rolled and air-cooled CP titanium is well known to have a texture from the factory. This texture and resulting elastic anisotropy were confirmed using two material characterization methods, resonant ultrasound spectroscopy (RUS) and electron backscatter diffraction (EBSD). The texture was further developed using a rolling mill to cold roll the titanium. A vacuum furnace set to a temperature of 550 C for one hour was used to stress relieve the titanium without reducing the texture. RUS and EBSD methods were used again to confirm the texture achieved by cold rolling. Well-characterized residual stresses were introduced with a shrink-fit ring and plug. The residual stress hole drilling method was used to characterize stresses in the rolling and transverse directions of the ring and plug assemblies. Stress profiles from hole drilling indicated some possible elastic anisotropic effects in two assemblies and are presented. However, more assemblies are needed to confirm the results. A stress determination technique with higher sensitivity may be necessary to substantiate assembly stress profile results.
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Experimental and Numerical Studies of Aluminum-Alumina CompositesGudlur, Pradeep 16 December 2013 (has links)
The preliminary goal of this study is to determine the effects of processing conditions, compositions and microstructural morphologies of the constituents on the physical and thermo-mechanical properties of alumina (Al_2O_3) reinforced aluminum (Al) composites. Composites with 0, 5, 10, 20 and 25 vol% Al_2O_3 were manufactured using powder metallurgy method. The elastic properties (Young's and shear modulus) and the coefficient of thermal expansion (CTE) of the composites were determined using Resonant Ultrasound Spectroscopy (RUS) and Thermo Mechanical Analyzer (TMA) respectively at various temperatures. Increasing compacting pressure improved relative density (or lowered porosity) of the composites. Furthermore, increasing the Al_2O_3 vol% in the composite increased the elastic moduli and reduced the CTE of the composites. Increasing the testing temperature from 25 to 450 oC, significantly reduced the elastic moduli of the composites, while the CTE of the composites changed only slightly with temperatures.
Secondly, the goal of this study is to determine the effect of microstructures on the effective thermo-mechanical properties of the manufactured Al-Al_2O_3 composites using finite element (FE) method. Software OOF was used to convert the SEM micrographs of the manufactured composites to FE meshed models, which were then used to determine the effective elastic modulus and CTE. It was observed that, effective modulus dropped by 19.7% when porosity increased by 2.3%; while the effective CTE was mildly affected by the porosity. Additionally, the effect of residual stress on the effective thermo-mechanical properties was studied, and the stress free temperature of the composites was determined.
Another objective of this study is to examine the stress-strain response of Al-Al_2O_3 composites due to compressive loads at various temperatures. Elastic modulus, yield stress and strain hardening parameters were determined from the stress-strain curves and their dependency on temperature, porosity and volume fraction were studied. The experimental results were compared with the numerical results. It was observed that high-localized stresses were present near the pores and at the interfaces between Al and Al_2O_3 constituents.
Finally, functionally graded materials (FGMs) with varying Al_2O_3 concentration (0, 5and 10 vol%) in Al were manufactured; and their stress-strain response and CTE were determined at various temperatures.
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