Materials Science and Engineering Commons^™

Understanding Size Effects In Small Scale Deformation: A Statistical Perspective, Sudharshan Phani Pardhasaradhi

Doctoral Dissertations

Recent experimental observations of micro-compression / tension tests indicate that as the size of test specimen decreases the yield strength increases. This raises a fundamental question: Why is smaller stronger? Is there a fundamental relationship between the size of a specimen and its intrinsic strength? This simple question pushes the limit of the current understanding of the physical mechanisms underlying material deformation, especially at small scales. In order to explain the experimental observations of the strength of small specimens containing a limited number of dislocations, a simple statistical model is developed. Two different types of randomness are introduced, viz., randomness …

Structure And Dynamics Of High Temperature Superconductors, Jennifer Lynn Niedziela

Doctoral Dissertations

High temperature superconductivity in iron based compounds has presented a series of complex problems to condensed matter physics since being discovered in 2008. The stalwart basis of condensed matter physics is the “strength in numbers" aspect of crystalline periodicity. Perfect crystalline periodicity has made possible the reduction of the questions of structural and electronic properties to single dimensions, increasing the tractability of these problems. Nevertheless, modern complex materials stretch these assumptions to their limits, and it is at this point where our work starts. Using neutron and x-ray scattering, we have conducted a series of studies on the structural disorder …

Lignin Yield Maximization Of Lignocellulosic Biomass By Taguchi Robust Product Design Using Organosolv Fractionation, Anton Friedrich Astner

Masters Theses

Lignin, a byproduct of the organosolv pretreatment process using lignocellulosic biomass from switchgrass (Panicum virgatum) and tulip poplar (Liriodendron tulipifera) is currently being explored for its potential use in the production of value-added chemicals and biobased polymers. Pretreatment is one of the most expensive processing steps in cellulosic biomass conversion. Optimization of the process is one of the major goals of the biomass-toethanol conversion process. Taguchi Robust Product Design (TRPD) provides an effective engineering experimental design method for optimizing a system and designing products that are robust to process variations. Given the results of several preliminary …

Wolfpack Gear Inc. Composite Frame Firefighter Backpack, Gabriel Mountjoy, Blair Ridings, Carl Drummond Buchenroth

Mechanical Engineering

No abstract provided.

Magnetic And Elastic Properties Of Magnetostrictive Tb6fe1-Xcoxbi2, Michael Richard Koehler

Doctoral Dissertations

The Tb6[6 sub]Fe1-x[1-x sub]Cox[x sub]Bi2[2 sub] (x = 0, 0.125, 0.25, and 0.375) family of compounds has been synthesized and investigated for magnetostrictive behavior using capacitance dilatometry. These measurements have been complemented by measurements of the elastic moduli using Resonant Ultrasound Spectroscopy (RUS), magnetization measurements (with a vibrating sample magnetometer (VSM)), as well as powder X-ray diffraction (XRD) and powder neutron diffraction measurements and heat capacity measurements.

Each of the compounds studied shows little magnetostriction at the Curie temperature but shows pronounced amounts of magnetostriction at temperatures below 100 K. Magnetostriction values of up to ~980 ppm have been discovered …

Atomistic Simulations Of Defect Nucleation And Intralayer Fracture In Molybdenum Disulphide During Nanoindentation, James A. Stewart

Graduate Theses and Dissertations

Molybdenum disulphide (MoS2) is a layered, hexagonal crystal that has a very low coefficient of friction. Due to this low coefficient of friction, MoS2 has become a well-known solid lubricant and liquid lubricant additive. As such, nanoparticles of MoS2 have been proposed as an additive to traditional liquid lubricants to provide frictional properties that are sensitive to different temperature and pressure regimes. However, to properly design these MoS2 nanoparticles to be sensitive to different temperature and pressure regimes, it is necessary to understand the mechanical response of crystalline MoS2 under mechanical loading. Specifically, the fundamental mechanism associated with the nucleation …

Pretreatment And Pyrolysis Of Rayon-Based Precursor For Carbon Fibers, Kokouvi Akato

Masters Theses

In this work, two rayon fibers were investigated as carbon fiber precursors. A detailed consideration has been applied to a domestically produced cellulose fiber to carbon fiber (CF) transition. This transition of precursor to carbon fiber can be subdivided into two stages: pyrolysis (thermal decomposition) of cellulose in air and high temperature treatment in an inert atmosphere. The specific objectives were to investigate the stabilization stage of the produced rayon with respect to changes taking place during thermal decomposition, and to evaluate the effects on the properties of the carbonized fiber. Changes taking place during the conversion process of the …

Phase Field Crystal Approach To The Solidification Of Ferromagnetic Materials, Niloufar Faghihi

Electronic Thesis and Dissertation Repository

The dependence of the magnetic hardness on the microstructure of magnetic solids is investigated, using a field theoretical approach, called the Magnetic Phase Field Crystal model. We constructed the free energy by extending the Phase Field Crystal (PFC) formalism and including terms to incorporate the ferromagnetic phase transition and the anisotropic magneto-elastic effects, i.e., the magnetostriction effect. Using this model we performed both analytical calculations and numerical simulations to study the coupling between the magnetic and elastic properties in ferromagnetic solids. By analytically minimizing the free energy, we calculated the equilibrium phases of the system to be liquid, non-magnetic …

Biaxial & Twist Testing Of Composite Carbon-Fiber Sandwich Panels For Automotive Racing Vehicles, Erik Eckberg

Materials Engineering

Composite sandwich panels were constructed with 4-ply plain weave carbon-fiber/epoxy face sheets in the 0^o/45^o/0^o/45^o orientation and 1/8^th inch Nomex honeycomb core. The panels were cut into 5-inch square test plates for mechanical testing. All testing was done on a fixture designed and fabricated by Pratt & Miller Engineering and installed on an Instron testing system at Cal Poly. The twist test was performed by supporting diagonal corners of the plate while simultaneously loading the opposite two corners at a crosshead rate of .06 in/min (ASTM 3044-94R11). Out of 10 panels tested, …

Corrosion Of Stainless Steel 316l And Astm F75 Cobalt Chromium Alloy During Immersion Testing In Silver Salt Solutions, Meagan Higgins

Materials Engineering

This study evaluates the potential effects of silver salts on biocompatible metals used for prostheses during the chemical reduction process to produce a silver antimicrobial layer on the metal’s surface. Samples of two biocompatible metals were obtained: Stainless Steel 316L and ASTM F75 Cobalt Chromium Alloy. Three different silver salts were also acquired: silver nitrate, silver sulfadiazine, and silver chloride. Specimens of each metal were cut to size using a 4-1/2 inch aluminum oxide, 40 grit, cut off wheel for metal, attached to a Dewalt Angle Grinder. The biocompatible metal samples were then subject to either Solution 1, water with …

Fabricating Replacement Glass Prisms For The Piedras Blancas Lighthouse, Daniel Garcken

Materials Engineering

The objective of this project was to design and create a process for manufacturing replacement glass prisms for the Piedras Blancas lighthouse and several other lighthouses nationwide. The prisms were designed to be in multiple metal arrays spread across the floor of the beacon room (the topmost room of the lighthouses). The prisms functioned to transmit extra, radiant light from the beacon light through the floor of the beacon room and disperse it into the maintenance room below. Using computer aided drafting (CAD) software, an original prism was measured and modeled; the corresponding mold was also modeled. G-codes for controlling …

An Exploratory Investigation Into How Cold Working Can Affect The Acoustic Performance Of Thin Aluminum Foil In A Ribbon Microphone, Alexander (Alex) Stanley

Materials Engineering

Ribbons of 4 μm thin 99.1% pure aluminum foil were cut and corrugated to replace the stock ribbon in an Apex 205 ribbon microphone. Prior to corrugation, half of the ribbons were sandwiched between two KimWipes and two pieces of cardstock then hammered to impart strain hardening. Each ribbon was placed into the microphone capsule and the frequency response of each ribbon was measured. A 10 second sine sweep from 20-20,000 Hz was played through a KRK Rokit 5 speaker and recorded through a ribbon microphone placed 6 inches away from the speaker cone. The signal generated by the ribbon …

The Synthesis And Characterization Of Gold And Silver Nanoparticles In Formal And Informal Settings, Mathew Wynn

Materials Engineering

Silver nanoparticles were synthesized through the reduction of AgNO3 using NaBH4. The borohydride anions were adsorbed onto silver nanoparticles. The repelling forces of the borohydride anions prevented the aggregation of particles, but the addition of an electrolyte or agitation induced aggregation. A yellow hue was given off by the silver nanoparticle sol that, using a spectrophotometer, had plasmon resonance at 386 nm. The silver nanoparticles were estimated to be 10 to 20 nm in diameter. Gold nanoparticles were synthesized through the reduction of HAuCl4 using Na3C6H5O7. The gold nanoparticle sol gave off a red hue that had plasmon resonance at …

Analyzing The Corrosion Resistance Of Ni-Shield 200 Coatings At Different Temperatures When Exposed To Sulphuric Acid, Alex Hussinger

Materials Engineering

Six steel samples each were twin wire arc sprayed with Hastelloy C-276 or Nickel-Shield 200 coatings approximately 0.020″ thick. These samples were then cut into 3″ by 3″ squares. A 2″ diamond grit hole saw was used to abrade and polish to a smooth surface a ring in the middle in order to get an O-ring mechanical seal. The samples were then weighed and loaded into a jig that started from the bottom up with a stainless steel plate, then the sample, then a Viton O-ring, a ¾″ thick glass plate with a 1 3/4″ hole cut in it, another …

Deposition, Characterization, And Fabrication Of A Zinc Oxide Piezoelectric Thin Film Microspeaker Using Dc Reactive Sputtering, Adam Olzick

Master's Theses

A piezoelectric microspeaker device that could be used in a variety of acoustic applications was designed and fabricated using a thin film ZnO layer that was reactively DC sputtered onto a single crystalline n-type silicon substrate. When tested the microspeaker did not produce sound due to complications in the etching process, the thickness of the diaphragms, and clamping effects. Instead, a characterization approach was taken and the structural, optical, electrical, and piezoelectric properties of the ZnO were investigated. Scanning electron microscopy, x-ray diffraction, and atomic force microscopy were utilized to discover the ZnO’s structural properties. Using the XRD and SEM, …

Blunt Impact Performance Evaluation Of Helmet Lining Systems For Military And Recreational Use, Jaclyn Siniora, Ryan Taylor, Darren Suey

Industrial Technology and Packaging

With the increasing problem in collegiate athletes experiencing injuries to the brain, different helmet liners where put to the test to see which liner provided athletes the greatest protection under specific conditions.

This senior project evaluates five different liners in football helmets. Each of the helmet liners were tested at three different temperatures: hot, cold, and ambient. Each helmet had seven different impact locations which were put to the test. The project was designed to be used to test ACH military combat liners as well. Due to shipping bottle necks the ACH combat liners have been left to future Cal …

Correlation Between 90o Tensile And 90o Flexural Properties For Thermoplastic Based Carbon-Fiber Composites, Amy Lautenbach

Materials Engineering

Thermoplastic matrix composites containing carbon fibers and 4 different resins (TP 1-TP 4) were tested in tension with the fibers at 90 degree to the longitudinal axis following ASTM D 3039-00. The tensile strengths varied from 5.07-13.87 ksi with TP 1 as the strongest, and TP 4 as the weakest. SEM images were taken of the fracture surface of the samples to explore the fiber-matrix interaction. The SEM images showed significantly more wetting of the fibers in the higher strength materials. The SEM images of the two stronger materials showed resin coating the fibers even after fracture while the two …

Compatibility Evaluation Of Glass/Epoxy Insulation For Use In Iter’S Central Solenoid Superconducting Electromagnets, Carolyn Grace Kidwell

Masters Theses

A variety of glass fiber types are being considered for use as insulation material in the central solenoid superconducting electromagnets for the International Thermonuclear Experimental Reactor (ITER). Before these materials can be used, a compatibility of these glass products with an epoxy matrix has to be characterized. In this study, three candidate glass types (1581, 7781, and 38050) were considered and their compatibility with a DGEBF epoxy matrix was determined via three-point flexure tests at room temperature (295K) and liquid nitrogen temperature (77K) and constant load flexure creep tests at room temperature. The material variables among these glass products were …

Characterization Of Mixing In A T-Style Microfluidic Chip, Brian Eric Harley

Master's Theses

The goal of this study is to characterize the mixing that occurs in a microfluidic chip. To characterize the mixing, the minimum length to complete mixing and evolution of mixing will be investigated. There are two types of mixing that occur within a microfluidic channel, diffusion and advection. In the beginning of the microfluidic chip, diffusion is the dominant form of mixing, and in the later portion of the microfluidic chip advection is the dominant form of mixing. The type of design used for this experiment was a zig zag geometry microfluidic chip with channel dimensions of 60 µm X …

Cryogenic Machining And Burnishing Of Az31b Magnesium Alloy For Enhanced Surface Integrity And Functional Performance, Zhengwen Pu

Theses and Dissertations--Mechanical Engineering

Surface integrity of manufactured components has a critical impact on their functional performance. Magnesium alloys are lightweight materials used in the transportation industry and are also emerging as a potential material for biodegradable medical implants. However, the unsatisfactory corrosion performance of Mg alloys limits their application to a great extent. Surface integrity factors, such as grain size, crystallographic orientation and residual stress, have been proved to remarkably influence the functional performance of magnesium alloys, including corrosion resistance, wear resistance and fatigue life.

In this dissertation, the influence of machining conditions, including dry and cryogenic cooling (liquid nitrogen was sprayed to …

Development And Validation Of Probabilistic Fatigue Models Containing Out-Life Suspensions, Noel S. Murray

Electronic Theses and Dissertations

Author's abstract: In the area of reliability engineering it is necessary to be confident that a component or system of components will not fail under use for safety and cost reasons. One major mechanism of failure to a mechanical component is fatigue. This is the repetitious motion of loading and unloading of the material, typically below the ultimate tensile strength of the material, which ultimately leads to a catastrophic failure. To ensure this does not happen, engineers design components based on tests to determine the life of these components. These tests are typically conducted on a bench type tester in …