Engineering Commons^™

Electrical Properties Of Srbi₂Ta₂O₉ Ferroelectric Thin Films At Low Temperature, Pingxiong Yang, David L. Carroll, John Ballato, Robert W. Schwartz

Mechanical and Aerospace Engineering Faculty Research & Creative Works

The temperature dependence of electrical properties for SrBi2Ta2O9 thin film capacitors with platinum electrodes (Pt/SBT/Pt) on silicon wafers was studied from 10 to 300 K. with a decrease in temperature from 300 to 200 K, the remanent polarization of the thin films shows about an 11% reduction from its 300 K value; however, it is reduced by about 87% reduction from its 200 K value when the temperature drops from 200 to 100 K. with a decrease to 200 K, the polarization fatigue was significant, and the capacitor shows an approximate 29% reduction in polarization from its initial value following …

The Effect Of Convection On Disorder In Primary Cellular And Dendritic Arrays, R. Trivedi, P. Mazumder, Surendra N. Tewari

Chemical & Biomedical Engineering Faculty Publications

Directional solidification studies have been carried out to characterize the spatial disorder in the arrays of cells and dendrites. Different factors that cause array disorder are investigated experimentally and analyzed numerically. In addition to the disorder resulting from the fundamental selection of a range of primary spacings under given experimental conditions, a significant variation in primary spacings is shown to occur in bulk samples due to convection effects, especially at low growth velocities. The effect of convection on array disorder is examined through directional solidification studies in two different alloy systems, Pb-Sn and Al-Cu. A detailed analysis of the spacing …

Coarsening Dynamics Of Biaxial Nematic Liquid Crystals, Nikolai V. Priezjev, Robert A. Pelcovits

Mechanical and Materials Engineering Faculty Publications

We study the coarsening dynamics of two- and three-dimensional biaxial nematic liquid crystals, using Langevin dynamics. Unlike previous work, we use a model with no a priori relationship among the three elastic constants associated with director deformations. Biaxial nematics possess four topologically distinct classes of defects, three of which have half-integer charge, while the fourth, which plays a minor role in coarsening, is of integer charge. We find a rich variety of coarsening behavior, including the presence of one, two, or three of the half-integer classes at late times, depending on the relative values of the elastic constants and the …

Student Perceptions Of Institutional And Instructor Based Techniques For Dealing With Academic Dishonesty, Donald D. Carpenter, Trevor S. Harding, Susan M. Montgomery, Nicholas H. Steneck, Eric Dey

Materials Engineering

Research suggests that a large percentage of engineering students engage in some form of academic dishonesty. To investigate this very serious concern, the authors have undertaken a research project on the Perceptions and Attitudes toward Cheating among Engineering Students (PACES). The premise of this research is that a combination of pressures, rather than malicious motivations, account for most student cheating. This paper focuses on a portion of the PACES survey; student opinions on what actions might prevent cheating. The authors examined data collected from approximately 350 engineering and pre-engineering undergraduate students at 5 institutions. In the survey, the students were …

A Comparison Of The Role Of Academic Dishonesty Policies Of Several Colleges On The Cheating Behavior Of Engineering And Pre-Engineering Students, Trevor S. Harding, Donald D. Carpenter, Susan M. Montgomery, Nicholas H. Steneck

Materials Engineering

While universities take a variety of approaches in dealing with academic dishonesty, current evidence suggests that institutions with honor codes have a significantly lower level of self-reported cheating as compared to nonhonor code institutions. This paper focuses on five institutions and their effectiveness in dealing with cheating, specifically among engineering or pre-engineering students. The authors' goal is to provide greater understanding of what institutional approaches appear to be most effective in minimizing cheating among this specific sub-group. The paper presents a predictive model of the extent of cheating among engineering students at these institutions using a variety of variables, including …

Segmented Roll For Casting Metal Strip, James R. Sauer, Ronald J. O'Malley, Robert S. Williams

Materials Science and Engineering Faculty Research & Creative Works

Casting molten metal using a segmented roll for casting continuous metal strip. A strip caster (10) for producing a continuous strip (18) includes a tundish for containing a melt and a pair of horizontally disposed water cooled composite casting rolls (84). The casting rolls are juxtaposed relative to one another for forming a pouring basin (16) for receiving molten metal. The composite rolls are formed from a plurality of annular segments (45). Each segment preferably includes at least a pair of coolant openings (34) and means for aligning the coolant openings, such as a pair of alignment openings (26). The …

Damage Accumulation Under Repeated Reverse Stressing Of Sn-Ag Solder Joints, Katherine C. Chen, A. Telang, J. G. Lee, K. N. Subramanian

Materials Engineering

To better understand the effect of repeated reverse stress in solder joints, a new testing method was developed. Tin-silver solder joints were fabricated, constrained between Cu blocks, and then subjected to repeated shear loading in a tensile tester. Constant strain amplitudes were applied to simulate service conditions. However, large loads were used to accelerate the damage accumulation. Microstructural features of the damage were very similar to those found with studies on thermomechanical fatigue (TMF) of small, single shear lap samples. Concentrated-shear banding or striations were observed to form along Sn dendrites. The load behavior of the solder with each cycle …

Corrosion Of Steel By Lead Bismuth Eutectic: Quarterly Report August September October 2002, John Farley

Transmutation Sciences Materials (TRP)

We continued with sputter depth profiling of 316 and 316L steel samples that have been exposed to LBE. We also calibrated the sputter depth profiling using a sample of SiO₂ on Si, and the SEM. This is a valuable independent determination of the thickness of oxide layers.

In the laboratory, progress continues using the XPS machine. Experiments have been performed on steel samples using Argon ions to mill away the surface of the sample, thereby making measurements as a function of depth. This "ion beam milling" proceeds slowly through the oxide layer that covers the steel sample. We are …

Primary Dendrite Distribution And Disorder During Directional Solidification Of Pb-Sb Alloys, Jun Hui, R. Tiwari, X. Wu, Surendra N. Tewari, R. Trivedi

Chemical & Biomedical Engineering Faculty Publications

Pb-2.2 wt pct Sb and Pb-5.8 wt pet Sb alloys have been directionally solidified from a single-crystal seed with its [100] orientation parallel to the growth direction, to examine the primary dendrite distribution and disorder of the dendrite arrays. The dendrite distribution and ordering have been investigated using analysis techniques such as the Gauss-amplitude fit to the frequency distribution of nearest and higher-order spacings, minimum spanning tree (MST), Voronoi polygon, and Fourier transform (FT) of the dendrite centers. Since the arrangement of dendrites is driven by the requirement to accommodate side-branch growth along the (100) directions, the FT images of …

Compressive Properties Of Zone-Directionally Solidified Β-Nial And Its Off-Eutectic Alloys With Chromium And Tungsten, R. Asthana, R. Tiwari, Surendra N. Tewari

Chemical & Biomedical Engineering Faculty Publications

The ordered intermetallic compound β-NiAl and its pseudo-binary off-eutectic alloys with 1 at.% tungsten and 9.7 at.% chromium were directionally solidified (DS) in the ‘floating-zone’ mode, and tested for compressive strength and fracture behavior in the temperature range 300–800 K. The dual-phase structures created by the DS of ternary NiAl alloys led to improvements in both the compressive strength and the ductility. The room-temperature (300 K) 0.2% compressive yield strength (CYS) of DS NiAl(W) (623 MPa) is larger than the CYS of DS NiAl(Cr) (565 MPa) and DS NiAl (435 MPa). The CYS of the three alloys dropped …

Virtual Surfaces, Director Domains And The Freedericksz Transition In Polymer Stabilized Nematic Liquid Crystals, Pavel A. Kossyrev, Jun Qi, Nikolai V. Priezjev, Robert A. Pelcovits, Gregory P. Crawford

Mechanical and Materials Engineering Faculty Publications

The critical field of the Freedericksz transition and switching dynamics are investigated for polymer stabilized nematic liquid crystals as a function of polymer concentration. A simple phenomenological model is proposed to describe the observed critical field and dynamic response time behaviors as a function of concentration. In this model the polymer fibrils form director domains, which are bounded by virtual surfaces with a finite anchoring energy. The Freedericksz transition occurs independently within each of these domains.

Magnetic Order In Yba₂Cu₃O₆₊ₓ Superconductors, Herbert A. Mook, Pengcheng Dai, Stephen M. Hayden, Arno Hiess, Jeffrey W. Lynn, Seunghun Lee, Fatih Dogan

Materials Science and Engineering Faculty Research & Creative Works

Polarized and unpolarized neutron diffraction has been used to search for magnetic order in YBa₂Cu₃O_6+x superconductors. Most of the measurements were made on a high quality crystal of YBa₂CU₃O_6.6. It is shown that this crystal has highly ordered ortho-II chain order, and a sharp superconducting transition. Inelastic scattering measurements display a very clean spin-gap and pseudogap with any intensity at 10 meV being 50 times smaller than the resonance intensity. The crystal shows a complicated magnetic order that appears to have three components. A magnetic phase is found at …

Development Of A Mechanistic Understanding Of High-Temperature Deformation Of Alloy Ep-823 For Transmutation Applications: Annual Progress Report (September 2001 – August 2002), Ajit K. Roy, Brendan O'Toole

Transmutation Sciences Materials (TRP)

The purpose of this project is to evaluate the elevated temperature tensile properties of Alloy EP-823, a leading target material for accelerator-driven waste transmutation applications. This alloy has been proven to be an excellent structural material to contain the lead-bismuth-eutectic (LBE) nuclear coolant needed for fast spectrum operations. Very little data exist in the open literature on the tensile properties of this alloy. The test material will be thermally treated prior to the evaluation of its tensile properties at temperatures relevant to the transmutation applications. The deformation characteristics of tensile specimens, upon completion of testing, will be evaluated by surface …

Fatigue Thresholds Of Cracks Resulting From Impact Damage To Γ-Tial, Trevor S. Harding, J. Wayne Jones

Materials Engineering

Significant research has been conducted in recent years on the γ-based titanium aluminide alloys. The low density of γ-TiAl relative to current nickel-based superalloys, has made it an attractive candidate for use in the low-pressure turbine blades of gas turbine engines . In addition to weight savings, the lower density leads to higher specific stiffness and good high temperature strength retention [1, 2 and 3]. However, the ordered crystal structure, typical of intermetallics, leads to inherently low room temperature ductility and fracture toughness. This raises serious concerns about the ability of this material to resist the formation of cracks at …

Modeling, Fabrication, And Optimization Of Niobium Cavities: Phase Ii Quarterly Report, Robert A. Schill Jr., Mohamed Trabia

Transmutation Sciences Materials (TRP)

Multipacting is one of the major loss mechanisms in rf superconductivity cavities for accelerators. This loss mechanism limits the maximum amount of energy/power supported by the cavities. Optimal designs have been identified in others’ studies. In practice, these designs are not easily manufactured. Chemical etching processes used to polish the cavity walls result in a nonuniform surface etch. A nonuniform surface etch will leave some unclean areas with contaminants and micron size particles. These significantly affect mutipacting. Further, a nonuniform etch will leave areas with damaged grain structure, which is not good for superconducting properties. Typically, the depth of chemical …

Hydrogen-Induced Embrittlement Of Candidate Target Materials For Applications In Spallation-Neutron-Target Systems: Quarterly Progress Report (June 01 – August 31, 2002), Ajit K. Roy, Brendan O'Toole

Transmutation Sciences Materials (TRP)

The primary objective of this task is to evaluate the effect of hydrogen on environment-assisted cracking of candidate target materials for applications in spallation-neutron-target (SNT) systems such as accelerator production of tritium (APT) and accelerator transmutation of waste (ATW). The materials selected for evaluation and characterization are martensitic stainless steels including Alloy HT-9, Alloy EP 823 and Type 422 stainless steel. The susceptibility to stress corrosion cracking (SCC) and hydrogen embrittlement (HE) of these materials are being evaluated in environments of interest using tensile specimens under constant load and slow-strain-rate (SSR) conditions. Further, the localized corrosion behavior of these alloys …

Use Of Positron Annihilation Spectroscopy For Stress-Strain Measurements: Quarterly Progress Report (June 1 – August 31, 2002), Ajit K. Roy

Transmutation Sciences Materials (TRP)

The purpose of this collaborative research project involving the University of Nevada Las Vegas (UNLV), the Idaho State University (ISU), and the Los Alamos National Laboratory (LANL) is to evaluate the feasibility of determining residual stresses in cold-worked, plastically-deformed, and welded materials using a nondestructive method based on positron annihilation spectroscopy. This technique uses γ-rays from a small MeV electron Linac to generate positrons inside the sample via pair production. This method is known to have capabilities of characterizing defects in thick specimens, that could not be accomplished by conventional positron technique or other nondestructive methods. The generated data will …

Modeling Corrosion In Oxygen Controlled Lbe Systems With Coupling Of Chemical Kinetics And Hydrodynamics-Task V: Final Report -Phase I 09/01/2001-08/30/2002, Samir Moujaes, Yitung Chen

Transmutation Sciences Materials (TRP)

The Lead-Bismuth eutectic (LBE) has been determined from previous experimental studies by the Russians and the European scientific community to be a potential material that can be used as a spallation target and coolant for the AAA proposed application. Properly controlling the oxygen content in LBE can drastically reduce the LBE corrosion to structural steels. However, existing knowledge of material corrosion performance was obtained from point-wise testing with only very sparse experimental data. Scientists have noticed that the concentration of oxygen dissolved in the liquid alloy could control the corrosion rate of steels exposed to Pb or Pb-Bi. At high …

Dielectric Properties Of A Ferroelectric Copolymer Langmuir–Blodgett Film, Mahantappa S. Jogad, Stephen Ducharme

Stephen Ducharme Publications

We report measurements of the real (epsilon prime) and imaginary (epsilon double-prime) parts of the relative complex permittivity of a Langmuir–Blodgett film of ferroelectric copolymer of vinylidene fluoride (70%) with trifluoroethylene (30%). The measurements were made in the temperature range of 35 to 125° C, and frequency range of 19 Hz to 5 MHz. The results indicate low frequency loss due to conduction and dielectric loss peak near the ferroelectric–paraelectric phase transition.

Electrically-Small Low Q Radiator Structure And Method Of Producing Em Waves Therewith, Craig A. Grimes, Dale M. Grimes, Faton Tefiku, Gang Lui

Chemical and Materials Engineering Faculty Patents

An electrically small radiator structure for radiating electromagnetic waves having an electrical size, k*a, with a value less than π/2 and above π/20,000 and configured to have at least a first and second magnetic, or electric, dipole element. Dipole elements are preferably oriented such that a source-associated standing energy value for the structure, or W_ds(t_R), is low, Radiative Q value preferably less than ⅓(k*a)³; and each of the elements, whether paired with respective electric dipole elements, is in electrical communication through a feed circuit to at least one power source. Further, a first …

Design And Analysis For Melt Casting Metallic Fuel Pins Incorporating Volatile Actinides: Quarterly Progress Report 5/16/02- 8/15/02, Yitung Chen, Randy Clarksean, Darrell Pepper

Fuels Campaign (TRP)

An important aspect of the Advanced Accelerator Applications (AAA) program is the development of a casting process by which volatile actinide element (i.e., americium) can be incorporated into metallic alloy fuel pins. The traditional metal fuel casting process uses an inductively heated crucible.

This process works well for the fabrication of metal fuel pins traditionally composed of alloys of uranium and plutonium, but does not work well when highly volatile actinides are included in the melt. The problem occurs both during the extended time period required to superheat the alloy melt as well as when the chamber must be evacuated. …

System Integration And Real-Time Control Architecture Of A Laser Aided Manufacturing Process, Mallikharjuna R. Boddu, Robert G. Landers, Srinivas Musti, Sanjeev Agarwal, Jianzhong Ruan, Frank W. Liou

Mechanical and Aerospace Engineering Faculty Research & Creative Works

This paper discusses a hybrid deposition–removal manufacturing system being developed at the University of Missouri--Rolla. The system consists of a laser system, five-axis CNC machining center, and powder feeder system. A description of the control software, real-time control architecture, and integration of various subsystems to build the hybrid system is given. The interaction of the real-time controller with various sensors and subsystems to monitor and regulate the process is presented. The communication between integrated process planning for the system and real–time control is also discussed in this paper.

Corrosion Of Steel By Lead Bismuth Eutectic: Quarterly Report For May-June-July 2002, John Farley

Transmutation Sciences Materials (TRP)

The goal of this project is to understand the basic science of corrosion in the steel/LBE system.

We are taking more data, typically using the newly installed X-ray Photoelectron Spectrometry (XPS) apparatus, and analyzing our existing data. Undergraduate students Denise Parsons and Julia Manzerova have helped a great deal in the analysis of the data. We can obtain the elemental composition as a function of position within the sample. This gives clues to the migration of materials, the composition of the protective oxide layer, and the basic science of the corrosion process. We found dramatic differences between the exposed and …

Correlation Between The Xps Peak Shapes Of Y1bu2cu3o7-X And Film Quality, Paul N. Barnes, Sharmila M. Mukhopadhyay, Timothy J. Haugan, Swaminathan Krishnaswami, Justin C. Tolliver, Iman Maartense

Mechanical and Materials Engineering Faculty Publications

X-ray photoelectron spectroscopy (XPS) depth profiling was used to investigate the compositional and chemical profile of a typical YBCO coated conductor architecture. Results of the process revealed that the Y(3d) photoelectronic peak shape in these films is very different from bulk YBCO. To investigate this, several samples of Y i Ba2Cu307_„ thin films were intentionally created of varying quality. The films were deposited on LaA10 3 by pulsed laser deposition with ./c. values ranging from poorly conducting up to several MA/cm2. Initial results indicated a potential correlation between the Y(3d) XPS peak shape (full-width-half-maximum) of the YBCO and the film …

Surface Switching Characteristics Of Variable Permittivity Dielectrics, Wayne Huebner, Eric J. Carleton

Materials Science and Engineering Faculty Research & Creative Works

Flashover voltage, lifetimes, and switch performance of insulators utilizing square thin and thick film electrodes were examined to determine the viability of using thin electrodes for reliable surface discharge switching. Gold, silver, and platinum were sputtered (0.25 µm) and screen printed (15 µm) onto Al₂O₃, TiO₂, and modified BaTiO₃ (MBT), then tested in air at 10⁵ Pa, under vacuum (10^-3/ torr), and while immersed in an insulating fluid, SF-2 (manufactured by 3M). For the measured range of 0.5 to 3 mm in air, the flashover voltage for all three insulators …

Observation Of Changes In The Atomic And Electronic Structure Of Single-Crystal Yba₂Cu₃O₆.₆ Accompanying Bromination, Lamine M. Dieng, Yasuhiro Inamura, Trevor A. Tyson, Mark C. Croft, Fatih Dogan, C. Y. Kim, Joseph C. Woicik, James M. Grow

Materials Science and Engineering Faculty Research & Creative Works

To ascertain the role of bromination in the recovery of superconductivity in underdoped YBa₂Cu₃O_6+y (YBCO), we have performed polarized multiple-edge x-ray-absorption fine structure (XAFS) measurements on normal (y~0.6) and brominated (Br/Cu~1/30, y~0.6) single crystals with superconducting transitions at 63 and 89 K, respectively. The brominated sample becomes strongly heterogeneous on an atomic length scale. Approximately one-third of YBCO is locally decomposed yet incorporated as a well-ordered "host" lattice as nanoscale regions. The decomposed phase consists of heavily distorted domains with an order not following that of the "host" lattice. Structurally, these domains are fragments of …

Hydrogen-Induced Embrittlement Of Candidate Target Materials For Applications In Spallation-Neutron-Target Systems: Annual Progress Report (May 2001 – May 2002), Ajit K. Roy, Brendan O'Toole

Transmutation Sciences Materials (TRP)

The primary objective of this task is to evaluate the effect of hydrogen on environment-assisted cracking of candidate target materials for applications in spallation-neutron-target (SNT) systems such as accelerator production of tritium (APT) and accelerator transmutation of waste (ATW). The materials selected for evaluation and characterization are martensitic stainless steels including Alloy HT-9, Alloy EP 823 and Type 422 stainless steel. The susceptibility to stress corrosion cracking (SCC) and hydrogen embrittlement (HE) of these materials are being evaluated in environments of interest using tensile specimens under constant load and slow-strain-rate (SSR) conditions. Further, the localized corrosion behavior of these alloys …

Development Of A Mechanistic Understanding Of High-Temperature Deformation Of Alloy Ep-823: Aaa Task-10 Quarterly (03/01, 2002 –05/31, 2002) Report, Ajit K. Roy, Brendan O'Toole

Transmutation Sciences Materials (TRP)

The objective of this task is to evaluate the elevated temperature tensile properties of Alloy EP-823, a leading target material for accelerator-driven waste transmutation applications. The test material will be thermally treated prior to evaluation of its tensile properties at temperatures relevant to the transmutation applications. The deformation characteristics of tensile specimens, upon completion of testing, will be evaluated by surface analytical techniques including scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The overall results are expected to provide a mechanistic understanding of high-temperature deformation behavior of Alloy EP-823 as a function of heat treatment.

Highlights of Accomplishment

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Suggestions For Establishing Centers For Engineering Education, Trevor S. Harding, Cynthia J. Finelli

Materials Engineering

No abstract provided.

P.A.C.E.S. - A Study On Academic Integrity Among Engineering Undergraduates (Preliminary Conclusions), Donald D. Carpenter, Trevor S. Harding, Susan M. Montgomery, Nicholas H. Steneck

Materials Engineering

Student academic dishonesty, commonly referred to as cheating, has become a serious problem at institutions of higher education. This is particularly true of engineering students who, according to previous research, are among the most likely to cheat in college. To investigate this concern, the authors have undertaken a research project on the Perceptions and Attitudes toward Cheating among Engineering Students (P.A.C.E.S.). The premise of this research is that a combination of pressures, rather than malicious motivations, account for most student cheating. The P.A.C.E.S study consists of a seven page, self-reported survey that investigates: (1) student definitions of academic dishonesty; (2) …