Thesis (Ph. D.)--University of Texas at Austin, 2003. / Vita. Includes bibliographical references. Available also from UMI Company.

Thesis (MScIng)--University of Stellenbosch, 2005. / Bibliography. Also available via the Internet.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2006. / Includes bibliographical references (leaves 112-123). Also available in electronic version.

Thesis (M.Phil.)--Hong Kong University of Science and Technology, 2007. / Includes bibliographical references (leaves 81-88). Also available in electronic version.

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This work is concerned with the prediction of short (SGF) and long glass fiber (LGF) orientation in a center-gated disk and end-gated plaque injection molding test geometry using a simulation method that has not been attempted previously. Previous work has used assumptions to simplify the fiber orientation geometry (assuming a thin cavity) or flow field (neglecting fountain flow and entry regions). LGF orientation is predicted in a center-gated disk injection molding geometry including the advancing front and simulating the sprue and gate region (SGM method) so that no assumption about fiber orientation at the mold entrance has to be made. Using a semi-flexible fiber model and orientation parameters obtained through rheology, increased agreement was found between predicted and experimentally obtained values of orientation using the SGM method and a semi-flexible fiber model than was found using a Hele-Shaw approximation. The SGM method was applied to the end-gated plaque to predict SGF orientation both along and away from the centerline using an objective (reduced strain closure model) and non-objective (strain reduction factor model) orientation model. The predicted values of the strain reduction factor model showed reasonable agreement with experimentally obtained values of orientation throughout the three-dimensional cavity when using orientation parameters fit to experimental orientation data. Furthermore it was found that the objective model predicted results very similar to the non-objective model suggesting that objectivity may not play a role in predicting orientation in more complex geometries such as an end-gated plaque. Finally, the SGM method was applied to the end-gated plaque geometry to predict LGF orientation using a rigid and semi-flexible fiber model. It was found that the SGM method and the semi-flexible fiber model provides orientation predictions that are similar to experimentally obtained values of orientation. / Ph. D.

Histotripsy is a nonthermal ultrasound therapy used to treat cancer noninvasively by tissue mechanical fractionation with cavitation bubble clouds. Histotripsy is conducted through focused ultrasound transducers, where the piezoceramic (PZT) plate or disc, which emits the ultrasound wave, is the fundamental unit of the transducer. For modular prototype histotripsy designs, these PZTs are housed in a 3D printed focused lens. However, 3D printing transducer components can be time consuming and expensive when scaling up manufacturing, and 3D printing is limited in material selection for transducer applications. This thesis investigates the use of a novel fabrication process for prototype focused ultrasound transducers, injection molding, with an in-house benchtop injection molding machine. Acoustic material properties for investigated injection molded materials, ABS, GPPS, 30% glass filled nylon, nylon 6/6, and nylon 101, are quantified experimentally. Single elements are constructed with injection molded lenses made from ABS, 30% glass-filled nylon, nylon 6/6, and nylon 101 on an in-house benchtop machine. Results show that injection molding is a novel feasible method for applications in focused ultrasound devices and the investigated plastics have favorable properties for developing prototype histotripsy transducers, comparable to 3D printed transducer housings. Future work aims to apply injection molding to various transducer designs and additional materials for focused ultrasound therapy devices. / Master of Science / Histotripsy is a cancer therapy that can noninvasively treat tumors without surgery. This is done through devices called focused ultrasound transducers which emit ultrasound waves to administer treatment to ablate tumors. These transducers are constructed using 3D printing methods, but this can be limiting when scaling up manufacturing or in material selection for transducer applications, therefore additional fabrication methods are needed. This thesis presents injection molding as a novel method for making transducer components with an in-house benchtop injection molding machine. Five plastic materials are investigated to determine ultrasound properties that would identify preferred transducer materials. Single element transducers are made from injection molded materials, tested, and compared with 3D printed single element transducers. Results of this thesis show that injection molding is a feasible manufacturing method capable of producing transducers for histotripsy, and researched materials have favorable properties for this application. In future research, additional injection molded materials should be investigated and multiple transducer designs created for injection molding fabrication. These injection molded transducers can be applied to histotripsy or applied to other focused ultrasound therapies.

This paper documents the investigation into injection molding, or die casting, a bulk metallic glass (BMG). A BMG is an amorphous metal of a thickness greater than 25 ��m, according to leading researchers in the field. This critical thickness differentiates a normal metallic glass from a "bulk" metallic glass. The impetus for studying the ability to process lies in the material properties of the BMG, which has twice the strength of steel and the ability to be formed much like a thermoplastic. An initial discussion of processing options and history precedes a detailed description of the machine concept and design, including the governing parameters placed on the design. An account of methods and materials used has been included, along with problems encountered and resultant remedies. The initial results consist of the verification of the machine concept and the ability to replicate nanometer-sized surface features from a mold. Design issues are addressed and the corresponding revisions described. The final machine revision shows an increase in process repeatability. A presentation of photographs, which show results of forming the BMG against both copper and stainless steel, is offered as a qualitative assessment of the processing capability. A discussion of considerations and paths forward has been included for future research using the machine that was developed, but these processing theories could also be carried over to other experiments. In the end, this study proves the ability to form extremely small surface features in cast BMG parts and makes suggestions on research avenues that may give a better understanding of the variables involved in processing BMG from the molten state. / Graduation date: 2003

Flax fiber-reinforced plastic composites have attracted increasing interest because of the advantages of flax fibers, such as low density, relatively high toughness, high strength and stiffness, and biodegradability. Thus, oilseed flax fiber derived from flax straw, a renewable resource available in Western Canada, is recognized as a potential replacement for glass fiber in composites. Among plastics, polyethylene is a suitable material for use as a matrix in composites. However, there are not many studies in this area. Therefore, the main goal of this research was to develop flax fiber-polyethylene (PE) biocomposites via injection molding and investigate the effect of material properties and processing parameters on their properties. <p>Alkali, silane, potassium permanganate, sodium chlorite, and acrylic acid treatments were employed to flax fiber to decrease the hydrophilic of fiber and improve the adhesion between the fiber and the matrix. All chemically treated fiber-HDPE biocomposites had higher tensile strength and lower water absorption compared with non-chemically treated ones. Acrylic acid treatment of the fiber resulted in slight increase in its degradation temperature; using this treated fiber resulted in biocomposites with the best performance. Therefore, the morphological, chemical, and thermal properties of acrylic acid treated fiber were also studied. <p>Linear Low Density Polyethylene (LLDPE) and High Density Polyethylene (HDPE) were the main matrices investigated in this research. Showing a high tensile strength and similar water absorption, HDPE was used as the matrix in further research. Flax fiber with 98-99% purity was chosen as reinforcement since the flax shive mixed with the fiber decreased the tensile and flexural properties but increased the water absorption of the biocomposite. <p>Acrylic acid-treated fiber-HDPE biocomposites had been developed through injection molding under different processing conditions. Increasing the fiber content of biocomposite increased its tensile and flexural strengths, especially flexural modulus, but its water absorption capacity also increased. It was possible to improve the mechanical properties of biocomposites and decrease the water absorption by adjusting injection temperature and pressure. Injection temperature had more influence on the quality of the biocomposite than injection pressure. Injection temperature lower than 195°C was recommended to achieve good composite quality. <p>Melts of HDPE and flax fiber-HDPE biocomposites were categorized as power-law fluids. Apparent viscosity, consistency coefficient, and flow behavior index of biocomposites were determined to study their flow behavior. The statistical relationship of these parameters with temperature and fiber content were modeled using the SAS and SPSS softwares. The injection filling time was related to the material rheological properties: biocomposites required longer filling time than pure HDPE. Low injection temperature also resulted in long filling time.<p>The thermal conductivity, thermal diffusivity, and specific heat of biocomposites containing 10, 20, and 30% fiber by mass were determined in the processing temperature range of 170 to 200°C. Fiber content showed a significant influence on the thermal properties of the biocomposites. The predicted minimum cooling time increased with the thickness of the molded material, mold temperature, and injection temperature, but it decreased with the ejection temperature.