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Constitutive Modeling Of The Thermo-Mechanics Associated With Crystallizable Shape Memory Polymers, Gautam Barot

Dissertations

This research addresses issues central to material modeling and process simulations. Here, issues related for developing constitutive model for crystallizable shape memory polymers are addressed in details. Shape memory polymers are novel material that can be easily formed into complex shapes, retaining memory of their original shape even after undergoing large deformations. The temporary shape is stable and return to the original shape is triggered by a suitable mechanism such heating the polymer above a transition temperature. Crystallizable shape memory polymers are called crystallizable because the temporary shape is fixed by a crystalline phase, while return to the original shape …

Dem Simulated Floor Pressure Induced By A Granular Column, Shawn A. Chester

Theses

At the end of the 19th century, H. A. Janssen discovered that the bottom floor pressure in a cylindrical container of granular material asymptotes exponentially to a value less than the weight of the material i.e., the pressure becomes independent of the fill height of the column. This phenomenon is investigated using discrete element simulations of inelastic, frictional spheres in a cylindrical vessel having a particle-to-cylinder diameter ratio at approximately 13.3 or 26.6, with varying bed heights in both cases. The axial pressure profile and the load experienced by a piston that is supporting the granular column are computed. In …

Effect Of Polymorphic Phase Transformations Within An Alumina Layer On The Ignition Of Aluminum Particles, Mikhaylo Aleksiyovych Trunov

Dissertations

Experimental measurements of aluminum ignition temperature and models used to describe aluminum ignition are reviewed. It is shown that the current models cannot describe ignition of aluminum powders of different sizes and ignited under various experimental conditions. The properties of and phase changes occurring in the alumina scale existing on the surface of aluminum particles at different temperatures are systematically studied. The mechanism of aluminum oxidation is quantified and a new simplified ignition model is developed.

Thermogravimetry was used to study the oxidation of aluminum powders of various particle sizes and surface morphologies in oxygen at temperatures up to 1500°C. …

Synthesis And Characterization Of Mechanically Alloyed Aluminum-Based Compounds As High Energy Density Materials, Xiaoying Zhu

Dissertations

A new type of metastable reactive powders for potential use as high energy density materials in propellants, explosives, and pyrotechnics was developed. These powders are intended to replace aluminum typically added to energetic formulations to increase reaction enthalpy and temperature. The new materials are metastable aluminum-based alloys, which enable achievement of substantially reduced ignition temperatures and accelerated bulk burn rates compared to aluminum. Titanium and lithium were used as alloying components. The materials properties and characteristics leading to their enhanced combustion performance were investigated. The powders were prepared using mechanical alloying and characterized using X-Ray Diffraction (XRD), Scanning Electron Microscopy …

Dry Magnetic Assisted Impaction Mixing Of Sub-Micron Boron And Barium Chromate For A Time Delay Composition, Ryan Barrow

Theses

The objective of this investigation is to improve the mixture homogeneity of, Boron and Barium Chromate, a delay composition called T-10, using a novel dry mixing technique, , called the Magnetic Assisted Impaction Mixing (MAIM). Two additional mixing methods, ultra-sonic mixing and shaker mixing (dry and wet), were used for comparative analysis, to evaluate the mixing effectiveness of the MAIM which was also compared to two Navy mixed T-l0 samples. Characterization of the homogeneity is described by how well boron is effectively distributed throughout the mixture, which is a challenging task since the mixture's composition is 3% Boron versus 97% …

Dynamic Simulations Of Particle Suspensions Subjected To An External Electric-Field, Xianjin Jiang

Dissertations

A numerical method is performed to study the suspension of polarizable particles in nonconductive solvents subjected to external electric fields. Such particles experience both hydrodynamic and electrostatic interactions. The hydrodynamic force acting on the particles is determined using the Stokesian dynamics method under the assumption that the Reynolds number is much smaller than 1, while the electrostatic force is determined by differentiating the electrostatic energy of the suspension, which is computed from the induced particle dipoles. In addition, the multiple image method is used to compensate for the electrostatic force when two particles are close to each other. Because the …

Modeling, Design, And Fabrication Of Pulsed Fluidic Micro-Actuators, Max Roman

Dissertations

The forced vibration of a thin flexible plate or membrane in a sealed cavity with a small opening can cause fluid to be pumped into and out-of the cavity. At particular frequencies and amplitudes of vibration, a streaming of vortex rings can occur near the orifice. These vortex rings move under their own self-induced momentum. Downstream of the opening the rings ultimately break up and can form a fully developed jet. This work is dedicated to the analysis, design, and fabrication of electrostatic micro fluidic actuators, which use the pulsing mechanism described above to generate a fluid flow. Particle Image …

The Effects Of Aging On Cardiac Mechanics, Samuel C. Lieber

Dissertations

It is well established that the aging heart exhibits left ventricular (LV) diastolic dysfunction and changes in mechanical properties, which have been attributed to alterations in the extracellular matrix (ECM). The investigators tested the hypothesis that the mechanical properties of cardiac myocytes significantly change with aging thereby contributing to the LV diastolic dysfunction. Cellular mechanical properties were determined by indenting cells with an atomic force microscope (AFM). The indentation results were interpreted by modeling the AFM probe as a blunted cone and determining an apparent elastic modulus (B) with classical infinitesimal strain theory (CIST). A commercially available finite element software …

Doppler Ultrasound Technique Used To Determine The Blood Flow Viscosity In The Middle Cerebral Artery Of A Canine Animal Model, Raj P. Ganpath

Theses

The cerebral blood flow velocity in the middle cerebral artery of an canine animal model was measured using the Doppler Ultrasound technique. A transducer was designed with a 20 MHz piezoelectric crystal and used for the application. An in vitro calibration system was designed and machined for the purpose of testing and calibrating every transducer before using it in vivo. Preliminary tests included experiments on the in vitro system and measurement of blood flow velocity in the human wrist artery (metacarpal artery). The effect of using different transmission media (agarose and gelatin) was determined through the many in vitro and …