UNT Theses and Dissertations - 6 Matching Results

Search Results

Angular Analysis of a Wide-Band Energy Harvester based on Mutually Perpendicular Vibrating Piezoelectric Beams

Description: The recent advancements in electronics and the advents of small scaled instruments has increased the attachment of life and functionality of devices to electrical power sources but at the same time granted the engineers and companies the ability to use smaller sources of power and batteries. Therefore, many scientists have tried to come up with new solutions for a power alternatives. Piezoelectric is a promising material which can readily produce continuous electric power from mechanical inputs. However, their power output is dependent upon several factors such as, system natural frequency, their position in the system, the direction of vibration and many other internal and external factors. In this research the working bandwidth of the system is increased through utilizing of two different piezoelectric beam in different directions. The dependency of output power with respect to rotation angle and also the frequency shift due to the rotation angle is studied.
Access: This item is restricted to UNT Community Members. Login required if off-campus.
Date: December 2016
Creator: Mirzaabedini, Sohrab
Partner: UNT Libraries

An Assessment of Uncommon Titanium Binary Systems: Ti-Zn, Ti-Cu, and Ti-Sb

Description: The current study focuses on phase stability and evolution in the titanium-zinc titanium-copper and titanium-antimony systems. The study utilized the Laser Engineering Net Shaping (LENS™) processing technique to deposit compositionally graded samples of three binary system in order to allow the assessment of phase stability and evolution as a function of composition and temperature the material is subjected to. Through LENS™ processing it was possible to create graded samples from Ti-xSb (up to 13wt%) and Ti-xCu (up to 16wt%). The LENS™ deposited gradient were solutionized, and step quenched to specific aging temperature, and the resulting microstructures and phase were characterized utilizing XRD, EDS, SEM, FIB and TEM. The Ti-Zn system proved incapable of being LENS™ deposited due to the low vaporization temperature of Zn; however, a novel processing approach was developed to drip liquid Zn onto Ti powder at temperatures above β transus temperature of Ti (882 ◦C) and below the vaporization temperature of Zn (907 ◦C). The product of this processing technique was characterized in a similar way as the graded LENS™ depositions. From measurements performed on Ti-Sb it seems that Sb could be a potential α stabilizer in Ti due to the presence of a mostly homogeneous α grains throughout the gradient; however, from XRD it can be understood that a titanium antimonide phase is present. From results obtained from the Ti-Zn samples, it can be surmised that the eutectoid reaction seems to be active, i.e. The eutectoid reaction is kinetically fast, as concluded by the presence of pearlitic structures. Finally, for the Ti-Cu system this work has been attempted to prove or disprove the existence of the Ti3Cu through the use of XRD and TEM SAD patterns. From XRD spectra collected there are peaks belonging to the Ti3Cu orthorhombic phase along with Ti2Cu and α-Ti phase. In ...
Date: May 2015
Creator: Brice, David
Partner: UNT Libraries

First Principle Calculations of the Structure and Electronic Properties of Pentacene Based Organic and ZnO Based Inorganic Semiconducting Materials

Description: In this thesis, I utilize first principles density functional theory (DFT) based calculations to investigate the structure and electronic properties including charge transfer behaviors and work function of two types of materials: pentacene based organic semiconductors and ZnO transparent conducting oxides, with an aim to search for high mobility n-type organic semiconductors and fine tuning work functions of ZnO through surface modifications. Based on DFT calculations of numerous structure combinations, I proposed a pentacene and perfluoro-pentacene alternating hybrid structures as a new type of n-type semiconductor. Based on the DFT calculations and Marcus charge transfer theory analysis, the new structure has high charge mobility and can be a promising new n-type organic semiconductor material. DFT calculations have been used to systematically investigate the effect of surface organic absorbate and surface defects on the work function of ZnO. It was found that increasing surface coverage of organic groups and decreasing surface defects lead to decrease of work functions, in excellent agreement with experimental results. First principles based calculations thus can greatly contribute to the investigating and designing of new electronic materials.
Date: May 2012
Creator: Li, Yun
Partner: UNT Libraries

Interspecimen Study of Bone to Relate Macromechanical, Nanomechanical and Compositional Changes Across the Femoral Cortex of Bone

Description: Mechanics of bone is widely studied and researched, mainly for the study of fracture. This has been done mostly on a macro scale. In this work hierarchical nature of bone has been explored to investigate bone mechanics in more detail. Flexural test were done to classify the bones according to their strength and deflection. Raman spectroscopy analysis was done to map the mineralization, collagen crosslinking changes across the thickness of the bone. Nanoindentation was done to map indentation hardness and indentation modulus across femoral cortex of the bone. The results indicate that the composition of the bone changes across the thickness of the femoral cortex. The hypothesis is confirmed as increase in mineralization, carbonate to phosphate ratio and collagen crosslinking shows the effect as increased indentation hardness and modulus and decreased deflection.
Access: This item is restricted to UNT Community Members. Login required if off-campus.
Date: May 2013
Creator: Nar, Mangesh
Partner: UNT Libraries

Orientation, Microstructure and Pile-Up Effects on Nanoindentation Measurements of FCC and BCC Metals

Description: This study deals with crystal orientation effect along with the effects of microstructure on the pile-ups which affect the nanoindentation measurements. Two metal classes, face centered cubic (FCC) and body centered cubic (BCC, are dealt with in the present study. The objective of this study was to find out the degree of inaccuracy induced in nanoindentation measurements by the inherent pile-ups and sink-ins. Also, it was the intention to find out how the formation of pile-ups is dependant upon the crystal structure and orientation of the plane of indentation. Nanoindentation, Nanovision, scanning electron microscopy, electron dispersive spectroscopy and electron backscattered diffraction techniques were used to determine the sample composition and crystal orientation. Surface topographical features like indentation pile-ups and sink-ins were measured and the effect of crystal orientation on them was studied. The results show that pile-up formation is not a random phenomenon, but is quite characteristic of the material. It depends on the type of stress imposed by a specific indenter, the depth of penetration, the microstructure and orientation of the plane of indentation. Pile-ups are formed along specific directions on a plane and this formation as well as the pile-up height and the contact radii with the indenter is dependant on the aforesaid parameters. These pile-ups affect the mechanical properties like elastic modulus and hardness measurements which are pivotal variables for specific applications in micro and nano scale devices.
Date: May 2008
Creator: Srivastava, Ashish Kumar
Partner: UNT Libraries

Polyethylene-layered double hydroxide and montmorillonite nanocomposites: Thermal, mechanical and flame retardance properties.

Description: The effect of incorporation two clays; layered double hydroxides (LDH) and montmorillonite layered silicates (MLS) in linear low density polyethylene (PE) matrix was investigated. MLS and LDH were added of 5, 15, 30 and 60 weight percent in the PE and compounded using a Brabender. Ground pellets were subsequently compression molded. Dispersion of the clays was analyzed using optical microscopy, SEM and XRD. Both the layered clays were immiscible with the PE matrix and agglomerates formed with increased clay concentration. The thermal properties were studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Both clays served as nucleation enhancers increasing recrystallization temperatures in the composites. Flame retarding properties were determined by using the flammability HVUL-94 system. LDH indicated better flame retarding properties than MLS for PE. The char structure was analyzed by environmental scanning electron microscopy. Mechanical properties were studied by tensile testing and Vickers microhardness testing apparatus.
Date: May 2008
Creator: Kosuri, Divya
Partner: UNT Libraries