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Progress Report 2011: Understanding compound phase transitions in Heusler alloy giant magnetocaloric materials

Description: Our goal is to gain insight into the fundamental physics that is responsible for magnetocaloric effects (MCE) and related properties at the atomic level. We are currently conducting a systematic study on the effects of atomic substitutions in Ni2MnGa-based alloys, and also exploring related full- and half-Heusler alloys, for example Ni-Mn-X (X=In, Sn, Sb), that exhibit a wide variety of interesting and potentially useful physical phenomena. It is already known that the magnetocaloric effect in the Heusler alloys is fundamentally connected to other interesting phenomena such as shape-memory properties. And the large magnetic entropy change in Ni2Mn0.75Cu0.25Ga has been attributed to the coupling of the first-order, martensitic transition with the second-order ferromagnetic—paramagnetic (FM-PM) transition. Our research to this point has focused on understanding the fundamental physics at the origin of these complex, compound phase transitions, and the novel properties that emerge. We synthesize the materials using a variety of techniques, and explore their material properties through structural, magnetic, transport, and thermo-magnetic measurements.
Date: December 13, 2011
Creator: Stadler, Shane
Partner: UNT Libraries Government Documents Department

Aligned, short-fiber composites by novel flow processing methods

Description: A hydrodynamic method has been employed to align short, reinforcing fibers in polymer matrix composite materials. Samples of composite materials were prepared and tested two at a time (one with randomly oriented fibers and the other with aligned fibers) to isolate and directly measure the effect on mechanical properties of aligning the fibers. Data were collected for the ultimate tensile strength, modulus of elasticity, and ultimate tensile strain of the composite samples prepared. Results show that the aligned fibers were approximately twice as effective (as randomly oriented fibers) at stiffening and strengthening the composite in the alignment direction. 5 figs, 20 refs.
Date: January 1, 1993
Creator: Guell, D. C.; Graham, A. L.; Papathanasiou, T. & Petrovic, J. J.
Partner: UNT Libraries Government Documents Department

MiniSAR composite gimbal arm development.

Description: An exploratory effort in the application of carbon epoxy composite structural materials to a multi-axis gimbal arm design is described. An existing design in aluminum was used as a baseline for a functionally equivalent redesigned outer gimbal arm using a carbon epoxy composite material. The existing arm was analyzed using finite element techniques to characterize performance in terms of strength, stiffness, and weight. A new design was virtually prototyped. using the same tools to produce a design with similar stiffness and strength, but reduced overall weight, than the original arm. The new design was prototyped using Rapid Prototyping technology, which was subsequently used to produce molds for fabricating the carbon epoxy composite parts. The design tools, process, and results are discussed.
Date: January 1, 2005
Creator: Klarer, Paul Richard & Winscott, Mark (Orion International, Albuquerque, NM)
Partner: UNT Libraries Government Documents Department

Radioactive rare gases and tritium in the sample return container, and the $sup 37$Ar and $sup 39$Ar depth profile in the Apollo 16 drill stem

Description: The gas was extracted from the sample return container from the Apollo 16 and 17 missions by adsorption on charcoal and activated vanadium metal. The hydrogen, argon, and radon were separated and counted to give the tritium, /sup 37/Ar, /suyp 39/Ar, and /sup 222 /Rn activities. The tritium and argon activities observed could be explained by diffusive losses of these gases from the fine material in the container. There was no excess tritium present in the Apollo 17 containers that could be attributed to solar tritons remaining from the intense flare of August 4, 1972. The /sup 222/Rn observed in the sample return container was interpreted as an emanation product from lunar fines and an emanation yield of 1 x 10/sup -4/ was calculated. This yield is consistent with the low radon content observed in the lunar atmosphere. The tritium, sup 37/Ar, / sup 39/Ar, and /sup 222/Rn activities and the K, Ca, Ti, Fe, and Mn contents were measured on a set of samples from the Apollo 16 deep drill stem at depths from 83 to 343 g/cm/sup 2/. The /sup 37/Ar and /sup 39/Ar activities combined with similar measurements at more shallow depth by Fireman and associates (SAO) give the complete activity proflle in the lunar regolith. Since /sup 37/Ar is produced mainly by the /sup 40/Ca(n, alpha )/su p 37/Ar reaction it is possible to determine the neutron production rate in the regolith as a function of the depth. The /sup 222/Rn extracted from the samples by vacuum melting was found to be lower than expected in some samples based upon their uranium contents. The hydrogen and helium contents of the drill stem samples were measured and found to be relatively uniform with depth in contrast to similar measurements on Apollo 15 and 17 drill stems. The …
Date: January 1, 1973
Creator: Stoenner, R.W.; Davis, R. Jr. & Bauer, M.
Partner: UNT Libraries Government Documents Department

Philosophy for nondestructive testing of fiber composites

Description: A discussion of a nondestructive testing philosophy for fiber composites is presented. The position is taken that the nondestructive test indications must be quantitatively correlated to the required engineering performance properties of the composite article. The currently unknown defect strcture in many fiber composites is discussed with respect to nondestructive testing. A few examples from the literature of the above described quantitative nondestructive testing of fiber composites are presented from the fields of acoustic emission and ultrasonics.
Date: April 1, 1977
Creator: Hamstad, M. A.
Partner: UNT Libraries Government Documents Department

Evolution of microstructure and mechanical properties in laser induced reaction coating of Al{sub 2}O{sub 3} on SiC/Al{sub 2}O{sub 3} composite

Description: Protection of a SiC(p)/Al2O3 composite (SiC particulate-reinforced Al{sub 2}O{sub 3}-matrix) at high temperature from deleterious reactions occurring within and with the surrounding environment is required for high temperature applications. Development of a continuous Al2O3 coating on SiC(p)/Al2O3 ceramic composite for such protection is achieved using the laser assisted in-situ reaction technique. The as-deposited alumina coating was analyzed using optical microscopy and XRD. The coated samples were also evaluated for mechanical properties using 3-point bend tests.
Date: December 31, 1996
Creator: Dahotre, N. B.; Xiao, C.; Boss, W.; McCay, M. H. & McCay, T. D.
Partner: UNT Libraries Government Documents Department

Materials Education: Opportunities over a Lifetime

Description: A report, in the form of abbreviated notes, of the 17th Biennial Conference on National Materials Policy ''Materials Education: Opportunities over a Lifetime'' held May 20-21, 2002 in College Park, MD, sponsored by the Federation of Materials Societies and the University Materials Council.
Date: October 28, 2003
Creator: Anderson, Iver E.; Schwartz, Lyle H.; Faber, Katherine T.; Cargill III, G. Slade & Houston, Betsy
Partner: UNT Libraries Government Documents Department

Superhydrophobic Materials Technology-PVC Bonding Techniques

Description: The purpose of the technology maturation project was to develop an enhanced application technique for applying diatomaceous earth with pinned polysiloxane oil to PVC pipes and materials. The oil infiltration technique is applied as a spray of diluted oil in a solvent onto the superhydrophobic diatomaceous earth substrate. This makes the surface take on the following characteristics: • wet‐cleanable • anti‐biofouling • waterproof • anti‐corrosion. The project involved obtaining input and supplies from VeloxFlow and the development of successful techniques that would quickly result in a commercial license agreement with VeloxFlow and other companies that use PVC materials in a variety of other fields of use.
Date: May 3, 2013
Creator: Hunter, Scott R. & Efird, Marty
Partner: UNT Libraries Government Documents Department

Design, Synthesis and Optoelectronic Properties of Monovalent Coinage Metal-Based Functional Materials toward Potential Lighting, Display and Energy-Harvesting Devices

Description: Groundbreaking progress in molecule-based optoelectronic devices for lighting, display and energy-harvesting technologies demands highly efficient and easily processable functional materials with tunable properties governed by their molecular/supramolecular structure variations. To date, functional coordination compounds whose function is governed by non-covalent weak forces (e.g., metallophilic, dπ-acid/dπ-base stacking, halogen/halogen and/or d/π interactions) remain limited. This is unlike the situation for metal-free organic semiconductors, as most metal complexes incorporated in optoelectronic devices have their function determined by the properties of the monomeric molecular unit (e.g., Ir(III)-phenylpyridine complexes in organic light-emitting diodes (OLEDs) and Ru(II)-polypyridyl complexes in dye-sensitized solar cells (DSSCs)). This dissertation represents comprehensive results of both experimental and theoretical studies, descriptions of synthetic methods and possible application allied to monovalent coinage metal-based functional materials. The main emphasis is given to the design and synthesis of functional materials with preset material properties such as light-emitting materials, light-harvesting materials and conducting materials. In terms of advances in fundamental scientific phenomena, the major highlight of the work in this dissertation is the discovery of closed-shell polar-covalent metal-metal bonds manifested by ligand-unassisted d10-d10 covalent bonds between Cu(I) and Au(I) coinage metals in the ground electronic state (~2.87 Å; ~45 kcal/mol). Moreover, this dissertation also reports pairwise intermolecular aurophilic interactions of 3.066 Å for an Au(I) complex, representing the shortest ever reported pairwise intermolecular aurophilic distances among all coinage metal(I) cyclic trimetallic complexes to date; crystals of this complex also exhibit gigantic luminescence thermochromism of 10,200 cm-1 (violet to red). From applications prospective, the work herein presents monovalent coinage metal-based functional optoelectronic materials such as heterobimetallic complexes with near-unity photoluminescence quantum yield, metallic or semiconducting integrated donor-acceptor stacks and a new class of Au(III)-based black absorbers with cooperative intermolecular iodophilic (I…I) interactions that sensitize the harvesting of all UV, all visible, and a broad spectrum of near-IR …
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Date: August 2017
Creator: Ghimire, Mukunda Mani
Partner: UNT Libraries

Active Transport of Nanomaterials Using Motor Proteins Final report for DOE-BES grant DE-FG03-03ER46024

Description: During the two year period of funding we have focused on the following topics: Guiding of microtubule movement on kinesin-coated, structured surfaces, directed assembly of oriented microtubule networks, and the interaction between synthetic materials and biological components in hybrid devices based on microtubules and kinesin motors. Additional efforts have been made and are still on- going in controlling the motor activity, and loading and unloading of cargo. In all aspects, the collaboration with the team at Sandia has been critical. A constant intellectual and material connection has been maintained by frequent visits, videoconferences, and exchanges of parts and supplies, such as microfabricated structures and motor proteins. The scientific advances made through this collaboration have been documented in seven publications in high- impact journals and an encyclopedia, discussed in invited talks at the annual meetings of MRS and ACS, and publicized by journalists in “The Scientist” and “Nature Materials Nanozone”. One double Ph.D. degree in Bioengineering and Nanotechnology has been completed (John Clemmens).
Date: March 16, 2005
Creator: Hess, Henry
Partner: UNT Libraries Government Documents Department

Phase transformation of PZST-86/14-5-2Nb ceramic under quasi-static loading conditions.

Description: Specimens of poled and unpoled PZST ceramic were tested under hydrostatic loading conditions at temperatures of -55, 25, and 75 C. The objective of this experimental study was to obtain the electro-mechanical properties of the ceramic and the criteria of FE (Ferroelectric) to AFE (Antiferroelectric) phase transformations of the PZST ceramic to aid grain-scale modeling efforts in developing and testing realistic response models for use in simulation codes. As seen in previous studies, the poled ceramic from PZST undergoes anisotropic deformation during the transition from a FE to an AFE phase at -55 C. Warmer temperature tests exhibit anisotropic deformation in both the FE and AFE phase. The phase transformation is permanent at -55 C for all ceramics tests, whereas the transformation can be completely reversed at 25 and 75 C. The change in the phase transformation pressures at different temperatures were practically identical for both unpoled and poled PZST specimens. Bulk modulus for both poled and unpoled material was lowest in the FE phase, intermediate in the transition phase, and highest in the AFE phase. Additionally, bulk modulus varies with temperature in that PZST is stiffer as temperature decreases. Results from one poled-biased test for PZST and four poled-biased tests from PNZT 95/5-2Nb are presented. A bias of 1kV did not show noticeable differences in phase transformation pressure for the PZST material. However, with PNZT 95/5-2Nb phase transformation pressure increased with increasing voltage bias up to 4.5kV.
Date: February 1, 2010
Creator: Broome, Scott Thomas; Scofield, Timothy W.; Montgomery, Stephen Tedford; Bauer, Stephen J. & Hofer, John H.
Partner: UNT Libraries Government Documents Department

Stress-displacement relation during fiber pullout

Description: During fiber pullout tests of fiber-reinforced composites, initial debonding, partial debonding, complete debonding at the interface, and fiber pullout occur sequentially. Adopting the shear lag model for stress analyses and the strength criterion for interfacial debonding, a bond length dependence of the initial debond stress is derived. During partial debonding, the stress initially increases with the increasing fiber displacement. The partial debond stress reaches a maximum value and begins to decrease with an accompanying decreasing fiber displacement until the interface is completely debonded. Theoretically, the stress-displacement curve shows a nose'' at the maximum debond stress. However, the pullout test is generally conducted under the condition of an increasing fiber displacement. Hence, at the maximum debond stress, the observed stress drops abruptly as the increasing fiber displacement type test obscures the nose-type characteristic.
Date: January 1, 1990
Creator: Hsueh, C.H.
Partner: UNT Libraries Government Documents Department

Theoretical models for the ultimate strength and flaw resistance of unidirectionally-reinforced ceramic-matrix composites

Description: Progress is reported on (1) interpretation of interface tests; (2) the effect of interface properties on flexural strength and its connection with uniaxial tensile strength, and (3) effect of interface properties on uniaxial tensile strength. Goal is to establish relations between manipulable material variables and mechanical response. The approach has been: (i) to hypothesize as to the key underlying physical mechanisms and to represent these hypotheses with model theoretical problems which can relate material parameters to observed mechanical behavior, (ii) to develop the necessary techniques to analyze the model problems; and (iii) to test the models by comparing the obtained results with experimental data. Phases 1 and 2 have been brought to satisfactory completion; work remains to be done on the third phase.
Date: January 1, 1992
Creator: Steif, P.S.
Partner: UNT Libraries Government Documents Department

Aligned, short-fiber composites by novel flow processing methods

Description: A hydrodynamic method has been employed to align short, reinforcing fibers in polymer matrix composite materials. Samples of composite materials were prepared and tested two at a time (one with randomly oriented fibers and the other with aligned fibers) to isolate and directly measure the effect on mechanical properties of aligning the fibers. Data were collected for the ultimate tensile strength, modulus of elasticity, and ultimate tensile strain of the composite samples prepared. Results show that the aligned fibers were approximately twice as effective (as randomly oriented fibers) at stiffening and strengthening the composite in the alignment direction. 5 figs, 20 refs.
Date: March 1, 1993
Creator: Guell, D. C.; Graham, A. L.; Papathanasiou, T. & Petrovic, J. J.
Partner: UNT Libraries Government Documents Department

Nonlinear seismic response of small reinforced-concrete shear wall structures

Description: The paper describes dynamic tests on small shear wall structures. The purpose of the tests was to obtain information on the behavior of reinforced concrete structures loaded into their nonlinear range. The small shear wall structures were subjected to classical sine-sweep vibration tests and to generated earthquake records. The results indicate that sine-sweep tests on degrading structures do not yield useful results because of fatigue effects and because steady-state motions cannot be achieved; however, the earthquake tests did yield useful information. From the earthquake tests results, responses were obtained that were plotted on computed linear and nonlinear non-dimensionalized response spectra. For loading within the linear range, the data indicate that the equivalent viscous damping for the test structures is about 12.5%. The test results also indicate that, in general, manipulation of the viscous damping coefficient cannot be used to predict nonlinear behavior. The more significant observation was that the effective stiffness of the shear wall structures, as determined from the dynamic tests, was only about 1/5 to 1/7 of the stiffness calculated using standard calculation methods.
Date: January 1, 1983
Creator: Endebrock, E.G. & Dove, R.C.
Partner: UNT Libraries Government Documents Department

Creating bulk nanocrystalline metal.

Description: Nanocrystalline and nanostructured materials offer unique microstructure-dependent properties that are superior to coarse-grained materials. These materials have been shown to have very high hardness, strength, and wear resistance. However, most current methods of producing nanostructured materials in weapons-relevant materials create powdered metal that must be consolidated into bulk form to be useful. Conventional consolidation methods are not appropriate due to the need to maintain the nanocrystalline structure. This research investigated new ways of creating nanocrystalline material, new methods of consolidating nanocrystalline material, and an analysis of these different methods of creation and consolidation to evaluate their applicability to mesoscale weapons applications where part features are often under 100 {micro}m wide and the material's microstructure must be very small to give homogeneous properties across the feature.
Date: October 1, 2008
Creator: Fredenburg, D. Anthony (Georgia Institute of Technology, Atlanta, GA); Saldana, Christopher J. (Purdue University, West Lafayette, IN); Gill, David D.; Hall, Aaron Christopher; Roemer, Timothy John (Ktech Corporation, Albuquerque, NM); Vogler, Tracy John et al.
Partner: UNT Libraries Government Documents Department

FWP executive summaries: basic energy sciences materials sciences and engineering program (SNL/NM).

Description: This report presents an Executive Summary of the various elements of the Materials Sciences and Engineering Program which is funded by the Division of Materials Sciences and Engineering, Office of Basic Energy Sciences, U.S. Department of Energy at Sandia National Laboratories, New Mexico. A general programmatic overview is also presented.
Date: July 1, 2006
Creator: Samara, George A. & Simmons, Jerry A.
Partner: UNT Libraries Government Documents Department

An acousto-ultrasonic NDE technique for monitoring material anisotropy

Description: A simpler and better way of monitoring the anisotropy of fiber-reinforced composite materials, based on the acousto-ultrasonic approach, is presented. In this approach, time of flight of the acousto-ultrasonic waves AU, rather than the stress wave factor, is measured. Two fundamental Lamb modes are generated under the first critical frequency: one is the first antisymmetric mode traveling with a slower velocity while the another is the first symmetric mode traveling with a faster speed. The later one is sensitive to the azimuthal angle and nearly nondispersive, and has a phase velocity very close to that of the bulk longitudinal wave of the material. Experimental data measured from two methods, TOF measurement and slope method, are compared with theoretical results; a good agreement is obtained for monitoring the material anisotropy. There is a great potential for this AU approach in material-property evaluation and in quantitative measurements of defects and debonding of fiber-reinforced composites. However, more studies are needed to better understand the effect of the fiber/matrix bonding on the measurements and to extract more information from the AU signals.
Date: August 1, 1992
Creator: Chien, Hual Te; Sheen, Shuh Haw & Raptis, A.C.
Partner: UNT Libraries Government Documents Department

Ceramic matrix composites by microwave assisted CVI

Description: Chemical vapor infiltration (CVI) processes for producing continuously reinforced ceramic composites are reviewed. The potential advantages of microwave assisted CVI are noted. Recent numerical studies of microwave assisted CVI are then reviewed. These studies predict inverted thermal gradients in fibrous ceramic preforms subjected to microwave radiation and suggest processing strategies for achieving uniformly dense composites. Comparisons are made to experimental results obtained using silicon based composite systems. The importance of microwave-material interactions is stressed. In particular, emphasis is placed on the role played by the relative ability of fiber and matrix to dissipate microwave energy. Results suggest that microwave induced inverted gradients can in fact be exploited using the CVI technique to promote inside-out densification.
Date: January 1, 1993
Creator: Currier, R.P. & Devlin, D.J.
Partner: UNT Libraries Government Documents Department
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