Engineering Commons^™

Processing Of Zrb2-Zrc-Zrxsiy Ceramic By Reactive Metal Penetration, Nischel B. Maheswaraiah

Open Access Theses & Dissertations

The processing of ZrB2-ZrC-ZrxSiy composite by reactive metal penetration was investigated as a successor to the ZrB2-SiC composites for hypersonic vehicles application, which cannot be used for extended time at temperatures greater than 1600C due to formation of SiO and CO gases. Zirconium (Zr), zirconium disilicide (ZrSi2), and boron carbide (B4C) were reacted in graphite crucibles for 60, 120, 180, and 240 minutes. Microscopy and x-ray diffraction (XRD) deduced the formation of a heterogeneous microstructure of ZrB2-ZrC-ZrxSiy precipitates surrounded by a solidified Zr-Si melt. Unreacted boron carbide was observed in samples held at 1860C for 60 minutes and 120 minutes, …

Resistive Switching Of Tin Dioxide (Sno2) For Memristor Applications, Sergio Fabian Almeida

Open Access Theses & Dissertations

In the last decades new electrical devices have been investigated in order to overcome problems caused by integrated circuit shrinking. Within these devices there is one that has attracted much attention due to its high scalability and simple structure. This device was proposed theoretically by Leon Chua in 1971 who gave it the name of "Memristor". In the recent years thin films structures composed of a metal/oxide/metal (MOM) stack have been linked to this new device, also known as "Resistive switching". There are several applications for the memristor; one of the most important is for resistive random access memory (ReRAM) …

Microstructure Investigation Of Al-Rich Titanium Aluminum Alloys, David Pham

Open Access Theses & Dissertations

The microstructures of Ti-Al alloys with 70-80 wt% Al were investigated. Aluminum wire (99.999%) and TiH₂ powder (99.7%) were used to produce the sample compositions inside a vertical tube furnace at 1600^oC in an Ar atmosphere. Argon is purified through a dehumidification and deoxidation system. Magnesium perchlorate Mg(ClO₄)₂ acts as a desiccant and titanium sponge pulls oxygen from the Ar in furnaces operating at 800^oC and 750^oC. X-ray diffraction and an optical microscope are used to identify phases and compositions

An Ab-Initio Study Of The Elastic Properties Of Important Group Iv Diborides At High Temperatures, Manny Gonzales

Open Access Theses & Dissertations

Presented is an ab-initio Molecular Dynamics (MD) study, employing the Density Functional Theory (DFT), of the lattice parameter, thermal expansion coefficients and elastic constants of ZrB₂, TiB₂ and HfB₂ as a function of temperature. The MD trajectories provide the equilibrium lattice parameters at finite temperatures, and the gradient of the energy from these equilibrium solutions is then used to calculate the components of the stiffness tensor. The results for ZrB₂ are shown to agree well with reported experimental results for the lattice parameters and elastic constants as a function of temperature.

Sensitivity Analysis Of The Johnson-Cook Plasticity Model For Hypervelocity Impacts: A Hydro-Code Study, Carlos David Castellanos

Open Access Theses & Dissertations

Computer simulations have been in use for decades in the modeling of hypervelocity impacts and general large deformation problems. Several computer codes have been developed to simulate this type of problems under a variety of geometric configurations and for any number of materials. These codes make use of several constitutive material models to simulate the response of the material under a variety of thermo-mechanical conditions. The Johnson-Cook constitutive model is widely used in the simulation hypervelocity impacts for the simulation of crater formation and even perforation of target structures. This thesis presents the results of a sensitivity study of this …

Selection Process, Modified Impact Testing And Failure Analysis Of An Electron-Beam-Melted Ti-6al-4v 3d Tessellation Based On The Eulerian Path Of The First Stellation Of The Rhombic Dodecahedron Open Unit Cell, Hugo Lopez

Open Access Theses & Dissertations

Ti-6Al-4V lattice block structures manufactured through the electron beam melting (EBM) process are a promising field in design and research due to great advantages that the alloy, the process and the final product offer. Three lattice block structures were manufactured through the electron beam process using an ARCAM A2 machine. The structures were designed using the MATERIALIZE^TM software and were designed around different types of unit cells. Compression testing was performed and one unit cell was selected due to its anisotropic behavior for modified impact testing. The same unit cell was used and it was scaled up to add …

Spectroscopic Study Of The Inhibition Of Calcium Oxalate Calculi By Larrea Tridentata, Luis Alonso Pinales

Open Access Theses & Dissertations

The causes of urolithiasis include such influences as diet, metabolic disorders, and genetic factors which have been documented as sources that aggravate urinary calculi depositions and aggregations, and, implicitly, as causes of urolithiasis. This study endeavors to detail the scientific mechanisms involved in calcium oxalate calculi formation, and, more importantly, their inhibition under growth conditions imposed by the traditional medicinal approach using the herbal extract, Larrea tridentata. The calculi were synthesized without and with Larrea tridentata infusion by employing the single diffusion gel technique. A visible decrease in calcium oxalate crystal growth with increasing amounts of Larrea tridentata herbal infusion …

The Reactivity Of A Zr-Si Melt With B4c At Ultrahigh Temperatures, Alvaro Vega Sandate

Open Access Theses & Dissertations

Surfaces with exceptional properties are needed for next generation materials. Hypersonic re-entry space vehicles or turbines are subjected to both oxidizing and neutral environments and nose-caps or wings on such vehicles could easily reach operating temperatures of over 2000°C. Ultrahigh temperature ceramics like ZrB2 and HfB2 have melting temperatures of 3245°C and 3380°C respectively. However, these materials need to be protected from oxidation, usually with an oxide layer. Zirconium is more affordable and will be used to study its reaction with B4C and ZrSi2.

Experimentation was conducted by melting Zr slugs into a B4C and ZrSi2 packed bed at 1860°C …

Hybrid Manufacturing: Integrating Stereolithography And Direct Print Technologies, Amit Lopes

Open Access Theses & Dissertations

The focus of this research was the development of a hybrid manufacturing system that integrates stereolithography (SL) and direct print (DP) technologies to fabricate three dimensional (3D) structural electronic devices within a single set-up. The capabilities of this new additive manufacturing (AM) technology was explored in the context of fabricating and prototyping complex electronic devices in which conformal shape, rugged and light-weight integration, and a natural resistance to reverse engineering are all of paramount importance. Consequently, electronic components can be tightly integrated together in a rugged, light-weight 3D structure of arbitrary form. This research is a continuing advancement of the …