This thesis details a study of the structural behavior of Hybrid-Composite Beams (HCB) consisting of a fiber reinforced polymer (FRP) shell with a concrete arch tied with steel prestressing strands.  The HCB offers advantages in life cycle costs through reduced transportation weight and increased corrosion resistance. By better understanding the system behavior, the proportion of load in each component can be determined, and each component can be designed for the appropriate forces. A long term outcome of this research will be a general structural analysis framework that can be used by DOTs to design HCBs as rapidly constructible bridge components. This study focuses on identifying the load paths and load sharing between the arch and FRP shell. Testing was performed by applying point loads on simple span beams (before placing the bridge deck) and a three beam skewed composite bridge system.  Curvature from strain data is used to find internal bending forces, and the proportion of load within the arch is found. Additionally, a stress integration method is used to confirm the internal force contributions.  The tied arch carries about 80% of the total load for the non-composite case without a bridge deck.  When composite with a bridge deck, the arch has a minimal contribution to the HCB stiffness and strength as it is below the neutral axis. For this composite case the FRP shell and prestressing strands resist about 85% of the applied load while the bridge deck carries the remaining 15% to the end diaphragms and bearings. / Master of Science

No description available.

A rigorous first order shear deformation theory (FSDT) is employed along with modified ABD parameters to analyze static and free vibration behavior of generally laminated beams and shafts. Different approaches for calculating composite beam stiffness parameters have been considered and the most accurate one that accounts for material couplings have been used to analyze static and free vibration behaviors of straight beams with different laminates and boundary conditions. In order to analyze curved beams, the term (1+z/R) is exactly integrated into ABD parameters formulation and an equivalent modulus of elasticity is used instead of traditional stiffness terms to account for both the deepness and material coupling of the beam structures. The model has been solved analytically for simply supported boundary conditions and the general differential quadrature (GDQ) technique has been used for other boundary conditions. The results for deflection, moment resultants, and natural frequencies of straight and curved beams with different deepness ratio (often called depth ratio), slenderness ratio, lamination, and boundary conditions are compared with those obtained from accurate three dimensional finite element simulations using ANSYS. The results were in close proximity to three dimensional finite element results. The model is then applied to transverse vibration analysis of multi-span generally laminated composite shafts with a lumped mass using GDQ. The results for natural frequencies are compared to experimental and other analytical models as well as finite element simulation. The results in the present analyses were found accurate. Conclusively, it has been shown that when considering more accurate stiffness parameters, a First Order Shear Deformation Theory can accurately predict static and free vibration behaviors of composite beams and multispan shafts of any deepness, lamination and boundary conditions.

Eutectic Fe-C, Ni-C and Fe-C-Si alloys have been solidified directionally in an electron-beam floating zone apparatus under carefully controlled conditions and the resulting morphologies in these alloy systems have been studied as a function of rate. In addition, the transition from the stable iron-graphite (grey iron) to the metastable iron-iron carbide (white iron) mode has been observed and has been related to the iron-carbon/iron-iron carbide double phase diagram by means of undercooling measurements. Interlamellar spacing measurements carried out on both the graphitic and carbidic modes using material of the same composition and purity under identical experimental conditions showed a λaR-1/2 and a λaR-1/3 relationship in the iron-graphite and iron-iron carbide eutectic systems, respectively. / Thesis / Doctor of Philosophy (PhD)

GaAs nanowires (NW) have been grown on Si (111) substrates by the self-assisted vapor-liquid-solid (VLS) mechanism using molecular beam epitaxy (MBE). Substrates were prepared with nano-patterned oxide templates using electron beam lithography (EBL) in order to achieve position controlled NW growth. Early experiments uncovered several key issues with regards to the patterning process. Cross-sectional lamella prepared using the focused-ion beam (FIB) technique were used to study the NW-substrate interface using transmission electron microscopy (TEM). Undesirable growth outcomes were found to be caused in part by an unintended residual layer of oxide. Uniform NW dimensions were then obtained by improving the pattern transfer method. The effects of deposition parameters on the growth results were then explored in further experiments. The first systematic study of the axial and radial growth rates of vertical NWs in the positioned array was conducted. It was proposed that the observed expansion of the Ga droplet in Ga-rich growth conditions results in a slight inverse tapered morphology, promoting significant radial growth. While the growth rates were shown to be approximately constant in time, their measured values were found to increase with increasing pattern pitch and decrease with increasing hole diameter. A phenomenological model was then developed based on the principle of mass conservation. A fit to the experimental data was obtained by calculating the collection of growth material supplied by a secondary flux of both gallium and arsenic species desorbing from the oxide surface between the NWs, subsequently impinging on the liquid droplet and NW sidewalls. The reduction of this contribution due to shading of the incident and scattered flux by neighboring NWs in the array was able to account for the differences in final NW morphologies observed with increasing pattern pitch. This model demonstrates the significant impact of secondary adsorption in patterned self-assisted NW growth. / Thesis / Doctor of Science (PhD)

No description available.

No description available.

This thesis describes how to evaluate a first-order approximation of the vibration induced on a beam that is vertically curved and experiences a moving load of non-constant velocity. The curved beam is applicable in the example of a roller coaster. The present research in the field does not consider a curved beam nor can similar research be applied to such a beam. The complexity of the vibration of a curved beam lies primarily in the description of the variable magnitude of the moving load applied. Furthermore, this motion is also variable. This thesis will present how this beam will displace in response to the moving load. The model presented can be easily manipulated as it considers most variables to be functions of time or space. The model will be compared to existing research on linear beams to ensure the unique response of a curved beam.

Several novel techniques for controlling, managing and utilizing high power diode lasers are described. Low pressure water spray cooling for a high heat flux system is developed and proven to be an ideal cooling method for high power diode laser arrays. In order to enable better thermal and optical performance of diode laser arrays, a new and simple optical element, the beam control prism, is invented. It provides the ability to accomplish beam shaping and beam tilting at the same time. Several low thermal resistance diode packaging designs using beam control prisms are proposed, studied and produced. Two pump cavity designs using a diode laser array to uniformly pump rod shape gain media are also investigated.

In order to fully understand the third order nonlinear optical response of materials under high irradiance excitation it is necessary to study the temporal and polarization dependence of nonlinear refraction and absorption. There are several existing approaches such as Z-scan and pump-probe techniques to determine those responses. As part of this work, these approaches will be briefly outlined before presenting beam deflection, applied from photothermal beam deflection, as an alternative experimental technique to determine the nonlinear refraction with its temporal and polarization dynamics. This technique measures the angle of the probe beam deflected via the index gradient of the material induced by strong excitation beam, to determine both the sign and magnitude of the nonlinear refraction. The temporal and tensor properties of the nonlinear refractive index can be determined by introducing a delay line, and by varying the polarization of the excitation and probe beam, respectively. To demonstrate the practicality of the beam deflection technique, we performed measurements on Fused Silica, Carbon Disulfide and Zinc Oxide. Each of these samples shows quite different nonlinear responses. Amorphous fused silica exhibits nonlinear refraction purely from instantaneous electronic contribution; while Carbon Disulfide shows a much slower response, originating not only from the electronic contribution but also from non-instantaneous nuclear movements (e.g. molecular orientation). These two contributions can be separated by varying the polarization direction of the excitation and probe beam. By introducing lock-in detection technique, a sensitivity of λ/5500 can be achieved. In Zinc Oxide, a wide-bandgap semiconductor, we measure both nonlinear refraction and two-photon absorption simultaneously. Therefore the beam deflection is a sensitive technique, which can be used to measure the time and polarization dynamics of the nonlinear response of the material