216 Matching Results

Search Results

Advanced search parameters have been applied.

Freeform fabrication of polymer-matrix composite structures

Description: The authors have developed, prototyped, and demonstrated the feasibility of a novel robotic technique for rapid fabrication of composite structures. Its chief innovation is that, unlike all other available fabrication methods, it does not require a mold. Instead, the structure is built patch by patch, using a rapidly reconfigurable forming surface, and a robot to position the evolving part. Both of these components are programmable, so only the control software needs to be changed to produce a new shape. Hence it should be possible to automatically program the system to produce a shape directly from an electronic model of it. It is therefore likely that the method will enable faster and less expensive fabrication of composites.
Date: May 1, 1997
Creator: Kaufman, S.G.; Spletzer, B.L. & Guess, T.L.
Partner: UNT Libraries Government Documents Department

Effective thermal conductivity of a thin composite material

Description: The thermal conductivity of a randomly oriented composite material is modeled using a probabilistic approach in order to determine if a size effect exists for the thermal conductivity at small composite thickness. The numerical scheme employs a random number generator to position the filler elements, which have a relatively high thermal conductivity, within a matrix having a relatively low thermal conductivity. Results indicate that, below some threshold thickness, the composite thermal conductivity increases with decreasing thickness, while above the threshold the thermal conductivity is independent of thickness. The threshold thickness increases for increasing filler fraction and increasing k{sub f}/k{sub m}, the ratio between filler and matrix thermal conductivities.
Date: December 1996
Creator: Phelan, P. E. & Niemann, R. C.
Partner: UNT Libraries Government Documents Department

Effective thermal conductivity of a thin, randomly oriented composite material

Description: The thermal conductivity of a randomly oriented composite material is modeled using a probabilistic approach in order to determine if a size effect exists for the thermal conductivity at small composite thicknesses. The numerical scheme employs a random number generator to position the filler elements, which have a relatively high thermal conductivity, within a matrix having a relative low thermal conductivity. The results indicate that, below some threshold thickness, the composite thermal conductivity is independent of thickness. The threshold thickness increases for increasing filler fraction and increasing k{sub f}/k{sub m}, the ratio between the filler and matrix thermal conductivities.
Date: October 1, 1997
Creator: Phelan, P.E. & Niemann, R.C.
Partner: UNT Libraries Government Documents Department

Vibrational Raman and Optical Studies of Cm in Zirconia-Based Pyrochlores and Related Oxides Matrices

Description: Raman spectroscopy has been employed to follow the phase behavior of Cm-Zr oxide materials as a function of Cm:Zr ratio. Three different structural phases, monoclinic, cubic and pyrochlore, are formed when the Cm:Zr ratio is varied from >0 to 1. Each phase produces a distinct Raman profile in the 100-700 cm{sup -1} spectral region. Up to 10 atom % Cm, the Raman spectra indicate that the monoclinic structure is dominant. Raman bands corresponding to the monoclinic phase are absent in samples containing 20 - 40 atom % Cm. Concomitantly, a band at -600 cm' broadens and increases in intensity with increasing curium content, indicating that the cubic phase is dominant in this concentration range. The pyrochlore oxide structure, which forms at 50 atom % Cm, generates three Raman bands (the center of mass are at 283, 387,495 cm-') out of six bands predicted by nuclear site group analyses. The strongest of these is at 283 cm-', and corresponds to the O-Cm-O bending mode. Details of these studies will be compared and discussed with data obtained for comparable systems containing selected analogous 4f-elements.
Date: November 2, 2001
Creator: Assefa, Z.
Partner: UNT Libraries Government Documents Department

Spectral Properties of Americium(III) in Silicate Matrices: Concentration-Dependent Up-Conversion Emission

Description: We have been pursuing the spectroscopic properties of actinide ions in silicate matrices. One facet of these studies involves the behavior of Stokes and anti-Stokes emissions exhibited by Am'' in these hosts. Several attributes have been found to influence the spectral profile, which include excitation wavelength, laser power, and dopant-concentration. Excitation with the 514.5 nm (19435 cm{sup -1}) line of argon laser provides anti-Stokes emissions at 21100 and -19920 cm{sup -1} in the boro-silicate matrices. This up-conversion was found to proceed through a multi-photon scheme, and its' efficiency increases with increased dopant concentration. Based on our concentration-dependent studies, the up-conversion is suggested to involve a cross-relaxation process [({sup 5}D{sub 1}, {sup 7}F{sub 0}{sup 7}F{sub 6}, {sup 7}F{sub 2})] between neighboring americium ions.
Date: November 2, 2001
Creator: Assefa, Z.
Partner: UNT Libraries Government Documents Department

Hydrogen absorption in epitaxial W/Nb(001) and polycrystalline Fe/Nb(110) multilayers studied in-situ by X-ray/neutron scattering techniques and X-ray absorption spectroscopy

Description: Hydrogen can be absorbed in large quantities by 100 {angstrom} thin Nb layers embedded in epitaxial W/Nb and polycrystalline Fe/Nb multilayers. The solubility and the hydrogen-induced structural changes of the host lattice are explored in-situ by small-angle neutron/X-ray reflectometry and high-angle diffraction. These measurements reveal for both systems that the relative out-of-plane expansion of the Nb layers is considerably larger than the relative increase of the Nb interplanar spacing indicating two distinctly different mechanisms of hydrogen absorption. In Fe/Nb multilayers, hydrogen expands the Nb interplanar spacing in a continuous way as function of the external pressure. In contrast, the Nb lattice expansion is discontinuous in epitaxial W/Nb multilayers: A jump in the Nb(002) Bragg reflection position occurs at a critical hydrogen pressure of 1 mbar. In-situ EXAFS spectroscopy also exhibits an irreversible expansion of the Nb lattice in the film plane for p{sub H{sub 2}}> 1 mbar. This can be regarded as a structural phase transition from an exclusively out-of-plane to a three-dimensionally expanded state at low and high hydrogen pressures, respectively.
Date: November 2, 1999
Creator: Klose, F.; Rehm, C.; Fieber-Erdmann, M.; Holub-Krappe, E.; Bleif, H. J.; Sowers, H. et al.
Partner: UNT Libraries Government Documents Department

Deformation texture development in a model composite system

Description: Model composites fabricated with a polycrystalline copper matrix and continuous tungsten fibres were deformed in plane strain compression with the fibres perpendicular to the loading axis and parallel to the direction of zero strain. The development of texture in the matrix due to deformation was measured using x-ray diffraction. It was observed that the macroscopic texture development in the composite was weaker than for unreinforced copper. The pattern of deformation in the matrix was quantified using experimental measurements and finite element method calculations. By carefully sectioning the composite after deformation, texture measurements were conducted for regions which exhibited characteristic types of deformation. These measurements showed that there is a variety of local textures (some weaker, some stronger than the texture in the unreinforced matrix) which when summed give the result of a weak global texture. This result is in agreement with the predictions from the computer simulations of Bolmaro et al.
Date: May 1, 1995
Creator: Poole, W.J.; MacEwen, S.; Kocks, U.F. & Embury, J.D.
Partner: UNT Libraries Government Documents Department

Microwave Processing of Simulated Advanced Nuclear Fuel Pellets

Description: Throughout the three-year project funded by the Department of Energy (DOE) and lead by Virginia Tech (VT), project tasks were modified by consensus to fit the changing needs of the DOE with respect to developing new inert matrix fuel processing techniques. The focus throughout the project was on the use of microwave energy to sinter fully stabilized zirconia pellets using microwave energy and to evaluate the effectiveness of techniques that were developed. Additionally, the research team was to propose fundamental concepts as to processing radioactive fuels based on the effectiveness of the microwave process in sintering the simulated matrix material.
Date: August 29, 2010
Creator: Clark, D.E. & Folz, D.C.
Partner: UNT Libraries Government Documents Department

SiO2 - polyethylene reflected critical assembly

Description: The Planet universal critical assembly machine was used to perform a series of three critical experiments. This experiment used HEU foils reflected by polyethylene and interleaved with plates of SiO{sub 2} glass and polyethylene. Only the experiment performed using the SiO{sub 2} matrix material is evaluated in this report. The assembly was delayed critical with 33 HEU foils or 17 units (sets of HEU foils). The critical assembly has an intermediate neutron spectrum, with 51.2% of the fissions occurring between 0.625 eV and 100 keV. The calculational results show good agreement with the experimental results.
Date: January 1, 2001
Creator: Brewer, R. W. (Roger W.) & Sanchez, R. G. (Rene G.)
Partner: UNT Libraries Government Documents Department

Impact of Spherical Inclusion Mean Chord Length and Radius Distribution on Three-Dimensional Binary Stochastic Medium Particle Transport

Description: We describe a parallel benchmark procedure and numerical results for a three-dimensional binary stochastic medium particle transport benchmark problem. The binary stochastic medium is composed of optically thick spherical inclusions distributed in an optically thin background matrix material. We investigate three sphere mean chord lengths, three distributions for the sphere radii (constant, uniform, and exponential), and six sphere volume fractions ranging from 0.05 to 0.3. For each sampled independent material realization, we solve the associated transport problem using the Mercury Monte Carlo particle transport code. We compare the ensemble-averaged benchmark fiducial tallies of reflection from and transmission through the spatial domain as well as absorption in the spherical inclusion and background matrix materials. For the parameter values investigated, we find a significant dependence of the ensemble-averaged fiducial tallies on both sphere mean chord length and sphere volume fraction, with the most dramatic variation occurring for the transmission through the spatial domain. We find a weaker dependence of most benchmark tally quantities on the distribution describing the sphere radii, provided the sphere mean chord length used is the same in the different distributions. The exponential distribution produces larger differences from the constant distribution than the uniform distribution produces. The transmission through the spatial domain does exhibit a significant variation when an exponential radius distribution is used.
Date: March 2, 2011
Creator: Brantley, P S & Martos, J N
Partner: UNT Libraries Government Documents Department

Uranium Metal Reaction Behavior in Water, Sludge, and Grout Matrices

Description: This report summarizes information and data on the reaction behavior of uranium metal in water, in water-saturated simulated and genuine K Basin sludge, and in grout matrices. This information and data are used to establish the technical basis for metallic uranium reaction behavior for the K Basin Sludge Treatment Project (STP). The specific objective of this report is to consolidate the various sources of information into a concise document to serve as a high-level reference and road map for customers, regulators, and interested parties outside the STP (e.g., external reviewers, other DOE sites) to clearly understand the current basis for the corrosion of uranium metal in water, sludge, and grout.
Date: September 25, 2008
Creator: Delegard, Calvin H. & Schmidt, Andrew J.
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

The thermal conductivity of carbon-fiber reinforced metal matrix composites

Description: High thermal conductivity metal matrix composites are being considered for heat sink applications in fusion energy, automotive and aerospace industries. The addition of P-120 carbon fibers was found to enhance the thermal conductivity of both aluminum and copper matrix composites. However, above 60 volume percent loading, the thermal conductivity of the composites tends to decrease. The titanium used as a fiber interface was found to be deleterious to the thermal conductivity of the copper matrix. Small diameter diamond particle additions tend to reduce the thermal conductivity of both the copper and aluminum matrix composites. This is explained in terms of the dominance of thermal boundary resistance due to the large surface to volume ratio of the small diamond particles.
Date: December 31, 1993
Creator: Dinwiddie, R. B; Beecher, S. C.; Arya, P. V. & Withers, J. C.
Partner: UNT Libraries Government Documents Department

Experimental Results in Support of Simulating Progressive Crush in Carbon-Fiber Textile Composites

Description: This report summarizes the findings of an experimental program conducted to support the modeling of the crush behavior of triaxial braid carbon fiber composites. The matrix material as well as braided panels and tubes were characterized in order to determine material properties, to assess failure modes, and to provide a test bed for new analytical and numerical tools developed specifically for braided composites. The matrix material selected by the ACC was an epoxy vinyl ester (Ashland Hetron 922). Tensile tests were used to compare two formulations-one used by the ACC and one recommended by the resin supplier. The latter was a faster reacting system and gelled in one-third the time of the ACC formulation. Both formulations had an average elongation at failure that was only half of the resin supplier's reported value. Only one specimen of each type came close to the reported elongation value and it was shown that failure invariably initiated at both surface and internal defects. Overall, the tensile properties of the two formulations were nearly identical, but those of the ACC system were more consistent. The properties of the ACC matrix formulation were measured in tension, shear, and compression and the average properties obtained in these tests are summarized.
Date: April 2, 2001
Creator: DeTeresa, S J; Allison, L M; Cunningham, B J; Freeman, DC; Saculla, M D; Sanchez, R J et al.
Partner: UNT Libraries Government Documents Department

High power X-ray welding of metal-matrix composites

Description: A method for joining metal-matrix composites (MMCs) by using high power x-rays as a volumetric heat source is provided. The method involves directing an x-ray to the weld line between two adjacent MMCs materials to create an irradiated region or melt zone. The x-rays have a power density greater than about 10{sup 4} watts/cm{sup 2} and provide the volumetric heat required to join the MMC materials. Importantly, the reinforcing material of the metal-matrix composites remains uniformly distributed in the melt zone, and the strength of the MMCs are not diminished. In an alternate embodiment, high power x-rays are used to provide the volumetric heat required to weld metal elements, including metal elements comprised of metal alloys. In an alternate embodiment, high power x-rays are used to provide the volumetric heat required to weld metal elements, including metal elements comprised of metal alloys.
Date: December 1, 1997
Creator: Rosenberg, Richard A.; Goeppner, George A.; Noonan, John R.; Farrell, William J. & Ma, Qing
Partner: UNT Libraries Government Documents Department

Failure Plane Orientations for Fiber Composites

Description: Using a recently developed failure theory for transversely isotropic fiber composites, it is shown how the orientation of the failure surface can be determined for transverse tension and compression. Experimental data on failure surface orientations have been obtained for four carbon fiber composite systems based on both thermoplastic and thermosetting matrix materials. Average compression failure planes for the different composite materials were measured to range from 31{sup o} to 38{sup o} from the load axis. Reasonable agreement was obtained between these measured angles and those predicted from application of the new failure theory.
Date: July 12, 2002
Creator: Christensen, R. M. & DeTeresa, S. J.
Partner: UNT Libraries Government Documents Department

High resolution interface nanochemistry and structure: Final project report, December 1, 1993--February 28, 1997

Description: Work includes studies of interface and grain boundary chemistry and structure in silicon nitride matrix/silicon carbide whisker composites, and in monolithic silicon nitride and silicon carbide synthesized by several different methods. Off-stoichiometric, impurity, and sintering aid elemental distributions in these materials (and other ceramics) have been of great interest because of expected effects on properties but these distributions have proven very difficult to measure because the spatial resolution required is high. The authors made a number of these measurements for the first time, using techniques and instrumentation developed here. Interfaces between metals and SiC are the basis for important metal matrix composites and contacts for high temperature SiC-based solid state electronic devices. The authors have investigated ultrapure interfaces between Ti, Hf, Ti-Hf alloys, Pt, and Co and Si-terminated (0001) 6H SiC single crystals for the first time.
Date: February 27, 1997
Creator: Carpenter, R.W. & Lin, S.H.
Partner: UNT Libraries Government Documents Department

The effect of interface damage on the microbuckling of unidirectional fiber-reinforced composites

Description: Fiber microbuckling is the primary failure mechanism in unidirectional fiber-reinforced composites under compression. Due to processing or service conditions, damage (e.g., microcracks) exists at fiber/matrix interfaces. The effect of damage on the microbuckling of fibers is investigated in the present study. Based on the micromechanics analysis, the damage at interfaces is modeled as a linear spring against interface sliding, and the spring constant depends on the damage level. It is established that the critical strain for fiber microbuckling is relatively insensitive to the interface damage, but increases rapidly with the fiber volume fraction.
Date: September 1, 1997
Creator: Huang, Y.; Liu, C.; Stout, M.G. & Hwang, K.C.
Partner: UNT Libraries Government Documents Department

Uranium isotopic composition and uranium concentration in special reference material SRM A (uranium in KCl/LiCl salt matrix)

Description: To help assure that analysis data of known quality will be produced in support of demonstration programs at the Fuel Conditioning Facility at Argonne National Laboratory-West (Idaho Falls, ID), a special reference material has been prepared and characterized. Designated SRM A, the material consists of individual units of LiCl/KCl eutectic salt containing a nominal concentration of 2.5 wt. % enriched uranium. Analyses were performed at Argonne National Laboratory-East (Argonne, IL) to determine the uniformity of the material and to establish reference values for the uranium concentration and uranium isotopic composition. Ten units from a batch of approximately 190 units were analyzed by the mass spectrometric isotope dilution technique to determine their uranium concentration. These measurements provided a mean value of 2.5058 {+-} 0.0052 wt. % U, where the uncertainty includes estimated limits to both random and systematic errors that might have affected the measurements. Evidence was found of a small, apparently random, non-uniformity in uranium content of the individual SRM A units, which exhibits a standard deviation of 0.078% of the mean uranium concentration. Isotopic analysis of the uranium from three units, by means of thermal ionization mass spectrometry with a special, internal-standard procedure, indicated that the uranium isotopy is uniform among the pellets with a composition corresponding to 0.1115 {+-} 0.0006 wt. % {sup 234}U, 19.8336 {+-} 0.0059 wt. % {sup 235}U, 0.1337 {+-} 0.0006 wt. % {sup 236}U, and 79.9171 {+-} 0.0057 wt. % {sup 238}U.
Date: July 1, 1997
Creator: Graczyk, D.G.; Essling, A.M.; Sabau, C.S.; Smith, F.P.; Bowers, D.L. & Ackerman, J.P.
Partner: UNT Libraries Government Documents Department

The Consistent Kinetics Porosity (CKP) Model: A Theory for the Mechanical Behavior of Moderately Porous Solids

Description: A theory is developed for the response of moderately porous solids (no more than {approximately}20% void space) to high-strain-rate deformations. The model is consistent because each feature is incorporated in a manner that is mathematically compatible with the other features. Unlike simple p-{alpha} models, the onset of pore collapse depends on the amount of shear present. The user-specifiable yield function depends on pressure, effective shear stress, and porosity. The elastic part of the strain rate is linearly related to the stress rate, with nonlinear corrections from changes in the elastic moduli due to pore collapse. Plastically incompressible flow of the matrix material allows pore collapse and an associated macroscopic plastic volume change. The plastic strain rate due to pore collapse/growth is taken normal to the yield surface. If phase transformation and/or pore nucleation are simultaneously occurring, the inelastic strain rate will be non-normal to the yield surface. To permit hardening, the yield stress of matrix material is treated as an internal state variable. Changes in porosity and matrix yield stress naturally cause the yield surface to evolve. The stress, porosity, and all other state variables vary in a consistent manner so that the stress remains on the yield surface throughout any quasistatic interval of plastic deformation. Dynamic loading allows the stress to exceed the yield surface via an overstress ordinary differential equation that is solved in closed form for better numerical accuracy. The part of the stress rate that causes no plastic work (i.e-, the part that has a zero inner product with the stress deviator and the identity tensor) is given by the projection of the elastic stressrate orthogonal to the span of the stress deviator and the identity tensor.The model, which has been numerically implemented in MIG format, has been exercised under a wide array of extremal loading ...
Date: November 1, 2000
Partner: UNT Libraries Government Documents Department

Description of the Canadian particulate-fill waste-package (WP) system for spent-nuclear fuel (SNF) and its applicability to light-water reactor SNF WPs with depleted uranium-dioxide fill

Description: The US is beginning work on an advanced, light-water reactor (LWR), spent nuclear fuel (SNF), waste package (WP) that uses depleted uranium dioxide (UO{sub 2}) fill. The Canadian nuclear fuel waste management program has completed a 15-year development program of its repository concept for CANadian Deuterium Uranium (CANDU) reactor SNF. As one option, Canada has developed a WP that uses a glass-bead or silica-sand fill. The Canadian development work on fill materials inside WPs can provide a guide for the development of LWR SNF WPs using depleted uranium (DU) fill materials. This report summarizes the Canadian work, identifies similarities and differences between the Canadian design and the design being investigated in the US to use DU fill, and identifies what information is applicable to the development of a DU fill for LWR SNF WPs. In both concepts, empty WPs are loaded with SNF, the void space between the fuel pins and the outer void space between SNF assemblies and the inner WP wall would be filled with small particles, the WPs are then sealed, and the WPs are placed into the repository.
Date: October 20, 1997
Creator: Forsberg, C.W.
Partner: UNT Libraries Government Documents Department

Identification and evaluation of appropriate backfills for the Waste Isolation Pilot Plant (WIPP)

Description: A backfill system has been designed for the Waste Isolation Pilot Plant (WIPP) which will control the chemical environment of the post-closure repository to a domain where the actinide solubility is within its lowest region. The actinide solubility is highly dependent on the chemical species which constitute the fluid, the resulting pH of the fluid, and the oxidation state of the actinide which is stable under the specific conditions. The use of magnesium oxide (MgO) has the backfill material not only controls the pH of the expected fluids, but also effectively removes carbonate from the system, which has a significant impact on actinide solubility. The backfill selection process, emplacement system design, and confirmatory experimental results are presented.
Date: August 1, 1998
Creator: Bynum, R.V.; Stockman, C. & Papenguth, H.
Partner: UNT Libraries Government Documents Department

Magnetic Separation for Nuclear Material Detection and Surveillance

Description: A high performance superconducting magnet is being developed for particle retrieval from field collected samples. Results show that maximum separation effectiveness is obtained when the matrix fiber diameter approaches the diameter of the particles to be captured. Experimentally, the authors obtained a single particle capture limit with 0.8{micro}m PuO{sub 2} particles with dodecane as a carrier fluid. The development of new matrix materials is being pursued through the controlled corrosion of stainless steel wool, or the deposition of nickel dendrites on the existing stainless steel matrix material. They have also derived a model from a continuity equation that uses empirically determined capture cross section values. This enables the prediction of high gradient magnetic separator performance for a variety of materials and applications. The model can be used to optimize the capture cross section and thus increase the capture efficiency.
Date: August 1, 1998
Creator: Worl, L.A.; Devlin, D.; Hill, D.; Padilla, D. & Prenger, F.C.
Partner: UNT Libraries Government Documents Department