Browsing by Subject "Micromechanics"
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ItemDevelopment of microfluidic systems for biological applications and their transport issues(2004) Li, Shifeng; Chen, Shaozhen.Microfluidic systems have been an exciting research area with a wide variety of promising biomedical applications. However, many challenging issues are still facing the research community with regard to mechanical as well as biological issues. The goal of this dissertation is to develop novel microfluidic systems targeting biomedical and life sciences applications with detailed investigation of thermal/fluid transport, materials and mechanics, and micromanufacturing processes. For a valveless micropump used for fluid delivery, a theoretical model is derived to analyze a lead zirconate titanate (PZT) microactuator and a system level analytical analysis is carried out for the PZT-actuated micropump. The effects of several important parameters and nondimensional variable groups on the actuator performances are also investigated. For rapid DNA analysis, a continuous-flow polymerase chain reaction (PCR) microchip with regional velocity control is developed. Finite element analysis is conducted to study the temperature uniformity of each reaction zone. A semi-analytical heat transfer model is developed to study heat transfer inside the PCR chip. Fluid velocity in the microchannel is measured using micro-particle image velocimetry (µ-PIV). The PCR chip is successfully amplified 90 base pair DNA sample. To connect a microfluidic device with other devices, novel polydimethysiloxane (PDMS) based interconnects have been fabricated. Microfabrication processes for through-hole type and “┌” type PDMS interconnects of glass and plastic capillary tubing have been developed. Leakage pressure, leakage flow rate, and pull-out force are characterized for these PDMS interconnects bonded to a variety of substrates. Two disposable analysis microchips in PDMS have been developed for protein/DNA detection. An established bead-based fluorescent assays for C-reactive protein (CRP) is used to characterize these chips. The detection limit of a single chamber chip is found to be as low as 0.1ng/ml. To increase detection capacity, a multiplechamber PDMS chip has also been developed. Fluid flow through the multiple-chamber microchip is improved by a back pressure compensation method. This has significantly improved the performances of the microchip. ItemExtreme energy absorption : the design, modeling, and testing of negative stiffness metamaterial inclusions(2013-08) Klatt, Timothy Daniel; Seepersad, Carolyn; Haberman, Michael R. (Michael Richard), 1977-A persistent challenge in the design of composite materials is the ability to fabricate materials that simultaneously display high stiffness and high loss factors for the creation of structural elements capable of passively suppressing vibro-acoustic energy. Relevant recent research has shown that it is possible to produce composite materials whose macroscopic mechanical stiffness and loss properties surpass those of conventional composites through the addition of trace amounts of materials displaying negative stiffness (NS) induced by phase transformation [R. S. Lakes, et al., Nature, 410, pp. 565-567, (2001)]. The present work investigates the ability to elicit NS behavior without employing physical phenomena such as inherent nonlinear material behavior (e.g., phase change or plastic deformation) or dynamic effects, but rather the controlled buckling of small-scale structural elements, metamaterials, embedded in a continuous viscoelastic matrix. To illustrate the effect of these buckled elements, a nonlinear hierarchical multiscale material model is derived which estimates the macroscopic stiffness and loss of a composite material containing pre-strained microscale structured inclusions. The nonlinear multiscale model is then utilized in a set-based hierarchical design approach to explore the design space over a wide range of inclusion geometries. Finally, prototype NS inclusions are fabricated using an additive manufacturing technique and tested to determine quasi-static inclusion stiffness which is compared with analytical predictions. ItemMicromechanical testing for the evaluation of chemo-mechanical alteration of CO₂ storage rocks(2017-08) Aman, Michael David; Espinoza, David N.; Balhoff, Matthew TThis thesis investigates the relationship between the chemically and mechanically coupled alteration of CO2-storage rocks during CO2 geological storage and the ensuing changes in rock properties. I analyzed how the scratch toughness and hardness varied with alteration by CO2-fluid mixtures by employing indentation and scratch test methodologies. Rock samples were selected from the Crystal Geyser site near Green River Utah, where a natural seepage of CO2 altered outcrops of the Entrada sandstone and Summerville siltstone formations near faults over tens of thousands of years. Results from tests on Entrada sandstone and Summerville siltstone from the Crystal Geyser site show that mechanical parameters measured with indentation (indentation hardness, Young’s modulus and contact creep compliance rate) and scratching (scratch hardness and scratch toughness) consistently indicated weakening of the rock after CO2-induced alteration. Decreases of measured parameters vary from 14% to 87%. In order to investigate the time scales of variation of mechanical and petrophysical properties differing to those before exposure, I conducted autoclave reaction experiments with Entrada sandstone and Summerville siltstone exposed to either de-ionized water or synthetic brine under reservoir pressure (9 10 MPa) and temperature (80°C) conditions for up to two weeks. I designed and constructed a scratch testing apparatus to conduct scratches on the laboratory altered rock samples. Scratch toughness and hardness show decreases of up to 60% in the case of Entrada sandstone and 92% in the case of Summerville siltstone after CO2-induced alteration in the laboratory. To understand chemical reactions during the laboratory alteration experiments, I conducted parallel experiments using powdered samples of Entrada sandstone and Summerville siltstone. I quantified aqueous ion concentrations for fluid samples collected from these autoclave experiments using analytical geochemistry. Dissolution of calcite and silicate cements are the primary reactions identified for both samples during the laboratory experiments. Recognizing the susceptibility of rock facies to CO2-related alteration at target CO2 geological storage formations is critical to ensuring the long-term mechanical stability and security of CO2 trapping. ItemOptical deformability : micromechanics from cell research to biomedicine(2001-12) Guck, Jochen Reinhold; Käs, Josef A.When a laser beam is incident on the surface of a transparent object, the optical surface forces, generated by the interaction of the light with the material, are directed away from the denser material and normal to its surface. This physical phenomenon can be used to probe the mechanical properties of dielectric materials. This optical deformability was exploited for the measurement of cellular elasticities with a novel micromanipulation device based on a two-beam fiber-based laser trap, the optical stretcher, which can generate surface forces from 1 pN–1 nN at frequencies ranging from static experiments to several MHz. The feasibility of accurately determining the elastic properties of biological cells with the optical stretcher was demonstrated by stretching human erythrocytes. A simple ray-optics treatment was used to explain and quantify the stresses on the surface of the cell, while their resulting deformation was recorded by video viii microscopy. Subsequent analysis of these data, modeling the erythrocyte as a thin shell, resulted in a cortical shear modulus of (1.3 ± 0.5) × 10–5 Nm–1, which is in excellent agreement with literature values. This result validates the ray-optics treatment. Higher developed, eukaryotic cells have an extensive threedimensional cytoskeleton throughout their cytoplasm, which renders them much more resistant to deformation. Using the optical stretcher, human neutrophils, normal and malignantly transformed mouse fibroblasts, and rat precursor cells were successfully stretched. These cells could be distinguished based on their optical deformability, with less differentiated cells showing lower elastic strength. The viability of the cells stretched was not jeopardized even when irradiated with 1.4 W of 780 nm laser light in both beams. By incorporation into a microfluidic flow chamber, the optical stretcher has the potential to measure up to several cells per minute, taking the speed of cell elasticity measurements to a new level and predisposing it for applications in biomedical diagnostic applications. As examples, the implications for cancer diagnosis and stem cell sorting are discussed in detail. Other applications of optical surface forces are envisioned. ItemOrganic transistor based circuits as drivers for planar microfluidic devices(2007-12) Nadkarni, Suvid Vikas, 1981-; Dodabalapur, Ananth, 1963-The work presented in this dissertation is focused on integrating organic transistor based circuits with planar microfluidic devices for discrete droplet handling. Discrete droplet based microfluidic systems are being increasingly investigated for lab-on-a-chip type applications. An essential component of a lab-on-a-chip system is the drive circuitry that runs the system. Conventionally, a variety of schemes have been implemented for acting as drivers for microfluidic devices. Organic transistor based circuits offer a viable and cost-effective option for serving as drivers for planar microfluidic devices. The magnitudes of voltages and the time scales involved in implementing these discrete droplet based systems are in good agreement with the values of voltages that can be reliably generated using organic transistor based circuits. Thus, the union of two cost-effective technologies with the ability to perform a wide variety of functions in a lab-on-a-chip type system would be highly desirable. A simple, planar microfluidic device with an open structure is implemented on a glass substrate. The device is optimized for reliable and repeatable performance using Cytop as the insulating dielectric. Cytop provides a highly hydrophobic surface for reversible wetting to take place on the application of electrical voltage. Various organic transistor based circuits are fabricated using Pentacene as the p-type semiconducting material and N,N'-bis(n-octyl)-dicyanoperylene-3,4:9,10-bis(dicarboximide) (PDI-8CN₂) as the n-type material. A top contact inverter, which is the most basic complementary metal oxide semiconductor circuit is fabricated and used as the driver for the planar microfluidic device. The output voltages generated by the inverter are used to actuate discrete water droplets over adjacent electrodes and also to perform merging of droplets, which is another basic functional operation that is performed on lab-on-a-chip type assemblies. Reliable and repeatable performance of the microfluidic device as well as the CMOS circuit is achieved. This work presents the first implementation of a discrete droplet based device driven by electrical voltages generated by an organic transistor based circuit. The physical mechanisms that are responsible for the motion of droplets have been investigated and contributions from electrowetting forces and dielectrophoretic forces have been resolved. ItemThe compressive failure of aligned fiber composite materials(1993) Arseculeratne, Ruwan, 1968-; Kyriakides, S.The present understanding of the compressive behavior of fibrous composites is somewhat limited. Reliable compressive test methods are one of the keys to understanding the complex compressive failure process in these materials. Compressive test devices that are currently in use often encounter difficulties with stress concentrations and instabilities. In addition, current micromechanical approaches have shown only moderate success in predicting the compressive strengths of these materials. This thesis examines some new experimental and micromechanical modeling aspects of compressive failure in fibrous composites. To achieve a better understanding of the compressive failure, two new specimen geometries were used to determine the compressive strength of an AS4 carbon fiber/PEEK composite. The first involved a thin-walled, hoop-wound ring loaded laterally in a confined ring loading device. These specimens reached maximum compressive strains as high as 1.08 % but exhibited a significant amount of scatter. The second involved circular cylindrical rod specimens with tapered and untapered test sections that were loaded axially in a special loading device. The tapered test specimens reached maximum compressive strains that were comparable to the ring specimens (1.04 %) and experienced less scatter. The constant cross section specimens did not achieve the same level of performance as the tapered specimens. However, the confined end condition was able to preserve the failed microstructure in these specimens by limiting the amount of post failure deformation. With the insight gained through these experiments and previous microbuckling modeling efforts, an alternate method of modeling this failure mode was undertaken. The model consists of individual fibers separated by matrix material. The model considers the fibers to be geometrically imperfect and also includes the nonlinearity of the matrix material. This analysis was able to show that a critical mechanism in microbuckling failure is the interaction between the geometric imperfections and material nonlinearity which produces a limit load type response