Over the past years, microfluidic systems have been rapidly developed from early single channel devices to current complex integrated analysis systems. The development in microfluidics has led to the realization of miniaturized applications in biomedical or chemical analysis. High throughput and automated microfluidic systems have made it possible to achieve biomedical or chemical instruments with new levels of performance and capability. However, because of the requirement of biomedical systems, disposed and optically transparent materials, high aspect ratio structures, and complicated fluidic connection are desirable. Conventional silicon microfabrication process may not overcome these limitations. In this work, micro molding replication technique is proposed as a low-cost polymer microfabrication technique. Based on this technique, four polymer based microfluidic devices, which are vortex micropump, discretized micromixer, carbon nanotube based flow sensor, and Surface Plasmon Resonance (SPR) imaging biosensor have been designed, fabricated and demonstrated. According to different applications, these individual devices can be integrated into an automated microfluidic analysis system to sense, regenerate, and deliver fluid volumes in the order of micro-liters. This miniaturized and integrated system can provide a high throughput, increased resolution, and better controllable environment. Using the integrated and automated microfluidic system, two biomedical experiments, including monitoring of bovine serum albumin (BSA) binding reaction with BSA antibodies, and cell adhesion properties under the influence of trypsin, have been conducted. / Lei Kin Fong Thomas. / "August 2005." / Adviser: Wen J. Li. / Source: Dissertation Abstracts International, Volume: 67-07, Section: B, page: 4065. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2005. / Includes bibliographical references (p. 88-98). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract in English and Chinese. / School code: 1307.

Composite materials are increasingly used in many industries due to the high strength and low weight properties that they exhibit. Since composites are becoming more popular, they are being used in applications such as aircraft, boats, wind turbine blades, and even sports equipment. Composite behavior is complicated since they are made up of two completely different materials such as strong thin fibers and a relatively weaker resin material that hold the fibers together. It is becoming more important to understand how composites behave in different situations so that equipment designers have reliable material information in order to design safe products that will not harm human life. Fabrication of composite material is not perfect and introduces defects such as the fibers being wavy and the matrix having voids. These defects decrease the strength of composites and if not accounted for in design, could be detrimental. To better understand the effects of these defects in composite materials, experimental tests can be performed to determine the material properties but it costs a lot of money and time. If the material properties of the composite do not match what is desired, different constituent materials are selected to create new composite specimens and the tests must be repeated which costs more time and more money. Computational approaches such as Finite Element Modeling (FEM) are gaining popularity as a way to predict composite behavior without the high cost of fabrication and equipment. Another advantage is the ability to test various materials and various defects by simply changing parameters in the computation. For this thesis, an FEM protocol is developed to model composites made from the material AS4/8552. First, the strength properties are extracted from a model without defects and then, defects such as waviness in the fiber and voids in the matrix are added to the model to see its effect. Knowing the effect of certain defects may help motivate composite fabricators to develop processes that eliminate detrimental defects.

Microscale fluid processes are an increasingly important subgroup of fluid mechanics. Applications for heat transfer and micro-electro-mechanical devices use flows on the scale of less than one hundred microns. This study is part of a larger work in which a multiphase, high shear environment is studied in a microchannel that has a depth of approximately 130 μm. Velocities are obtained using non-invasive imaging schemes. Laser induced fluorescent Particle Image Velocimetry (PIV) is used to analyze the velocity distribution in the microchannel. Multiple image processing techniques are used to optimize the images for correlation calculations. Velocity profiles for three flow rates and three void fractions (one of which is zero) are developed experimentally. The effect of the microbubbles on the PIV analysis is shown to flatten the profile through one primary mechanism and possibly a secondary, less dominant mechanism. / Graduation date: 2006

The effect of unsteady thermocapillary convection on the mass transfer rate of a solute between two immiscible liquids within a rectangular microscale channel with differentially heated sidewalls was numerically investigated. A computational fluid dynamic code in Fortran77 was developed using the finite volume method with Marker and Cell (MAC) technique to solve the governing equations. The discrete surface tracking technique was used to capture the location of the moving liquid-liquid interface. The code produced results consistent with those reported in published literature. The effect of the temperature gradients, the aspect ratio, the viscosity of liquid, and the deformation of the interface on the mass transfer rate of a solute were studied. The mass transfer rate increases with increasing temperature gradient. The improvement of the mass transfer rate by the thermocapillary convection was found to be a function of the Peclet number (Pe). At small Pe, the improvement of the mass transfer rate increases with increasing Pe. At high Pe, increasing the Pe has no significant effect on increasing the mass transfer rate. Increasing the aspect ratio of the cavity up to 1 increases the mass transfer rate. When the aspect ratio is higher than 1, the vortex moves only near the interface, resulting in decreasing the mass transfer rate. By increasing the viscosity of the liquid in top phase, the maximum tangential velocity at the interface decreases. As a result, the improvement of the mass transfer rate decreases. The deformation of the interface has no significant effect on the improvement of the mass transfer rate. By placing the heating source at the middle of the cavity, two steady vortices can be induced in a cavity. As a result, the mass transfer rate is slightly enhanced than that in the system with one vortex. By reversing the direction of the temperature gradient, the mass transfer rate decreases due to the decrease in the velocity of bulk fluid. The thermocapillary convection also promotes the overall reaction process when the top wall of the cavity is served as a catalyst. / Graduation date: 2005

A two-dimensional model was developed to predict concentration profiles from passive, laminar mixing of concentration layers formed in a fractal-like merging channel network. Both flat and parabolic velocity profiles were used in the model. A physical experiment was used to confirm the results of the model. Concentration profiles were acquired in the channels using laser induced fluorescence. The degree of mixing was defined and used to quantify the mixing in the test section. Although the results of the experiment follow the trend predicted by the two-dimensional model, the model under predicts the results of the experiment. A three-dimensional CFD model of the flow field in the channel network was used to explain the discrepancies between the two-dimensional model and the experiment. For the channel network considered, the degree of mixing is a function of Peclet number. The effect of geometry on the degree of mixing is investigated using the two-dimensional model by varying the flow length, the width of the inlet channels, and the number of branching levels. A non-dimensional parameter is defined and used to predict an optimum number of branching levels to maximize mixing for a fixed inlet channel width, total length, and channel depth. / Graduation date: 2003

The goal of this thesis is to determine the relationship between the macroscopic stress and the macroscopic strain for a variety of complex multiphase materials exhibiting rate-independent non-linear response at the micro-scale, based on experimental data obtained both at the local and macroscopic scales. A micro-macro secant mean field model (SMF model) based on the result of Eshelby and the approach of Mori and Tanaka is developed to model the behaviour of three particular systems which we have worked out by ourselves: 1) a ferrite-martensite steel produced by rolling in which we quantify the plastic anisotropy due to the morphological texture in terms of the Lankford's coefficient and pseudo yield surface; 2) a composite made of two continuous and interpenetrating phases: an aluminium matrix reinforced by a preform of sintered Inconel601 fibres. We quantify the coupled effects of temperature and phases co-continuity on the phases and overall stresses; 3) a TRIP-aided multiphase steel, in which the dispersed metastable austenite phase transforms to martensite. We derive the relationship between the overall uniaxial elastoplastic response and the progress of phase transformation, itself influenced by the thermodynamical, microstructural and mechanical properties. The stress-state dependence of the martensitic transformation is enlightened and explained. We demonstrate the existence of thermomechanical treatments leading to optima of ductility and strength-ductility balance. Finally, we show that the formability of TRIP-aided multiphase steels depends on the stability criterion.

This study introduces a time-dependent micromechanical model for a viscoelastic-viscoplastic analysis of particle-reinforced composite and hybrid composite. The studied particle-reinforced composite consists of solid spherical particle and polymer matrix as constituents. Polymer constituent exhibits time-dependent or inelastic responses, while particle constituent is linear elastic. Schapery's viscoelastic integral model is additively combined with a viscoplastic constitutive model. Two viscoplastic models are considered: Perzyna's model and Valanis's endochronic model. A unit-cell model with four particle and polymer sub-cells is generated to obtain homogenized responses of the particle-reinforced composites. A time-integration algorithm is formulated for solving the time-dependent and inelastic constitutive model for the isotropic polymers and nested to the unit-cell model of the particle composites. Available micromechanical models and experimental data in the literature are used to verify the proposed micromechanical model in predicting effective viscoelasticviscoplastic responses of particle-reinforced composites. Filler particles are added to enhance properties of the matrix in the fiber reinforced polymer (FRP) composites. The combined fiber and particle reinforced matrix forms a hybrid composite. The proposed micromechanical model of particle-reinforced composites is used to provide homogenized properties of the matrix systems, having filler particles, in the hybrid composites. Three-dimensional (3D) finite element (FE) models of composite's microstructures are generated for two hybrid systems having unidirectional long fiber and short fiber embedded in cubic matrix. The micromechanical model is implemented at the material (Gaussian) points of the matrix elements in the 3D FE models. The integrated micromechanical-FE framework is used to examine time-dependent and inelastic behaviors of the hybrid composites.

No description available.

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 73-79).

Thesis (Ph. D.)--School of Mechanical Engineering, Georgia Institute of Technology, 2004. Directed by Said I. Abdel-Khalik. / Includes bibliographical references (leaves 292-296).