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Surfacing the Void

Description: Surfacing the Void is an exploration of surface design in relationship to the topic of voids. For the purpose of this paper, two types of void were addressed: shelters and hulls. The theme behind the sculptural works dealt with negative spaces as an analogy for the voids in people's lives. The goal was to find a way for the surfaces to elicit an emotional response from the viewer that correlates to the impression of either shelter or hull. Keeping this in mind, each experiment was approached with how to best represent the meaning of void being manifested. Imagery was applied during different states of the clay: wet, dry, and fired. Methods of exploration included texturing, drawing, stenciling, stamping, incising, decoupage and covering the surfaces with textiles.
Date: May 2002
Creator: Williamson, Melanie L.
Partner: UNT Libraries

First positron annihilation lifetime measurement of Pu

Description: We have made the first measurement of defects in an aged sample of {delta} phase, Ga stabilized Pu, using positron annihilation lifetime spectroscopy. This measurement validates the procedure necessary to perform measurements on this highly toxic material and obtain data representative of sample conditions. Comparison of the positron annihilation lifetime analysis of the data with calculated values suggests that He filled vacancies or vacancy clusters dominate the defect population. Such defects are the necessary precursor to void growth and swelling. The evolution of defects resulting from the radioactive decay of Pu during its life in the stockpile is one of the unknown quantities affecting our confidence in predictions of the limit on stockpile components. Radiation damage leads to changes in the size and strength of metals studied for reactor and accelerator use and similar effects may be expected in Pu. The evolution of radiation produced vacancies into larger void structures and accompanying macroscopic swelling may occur in Pu at some age. A detailed understanding of the defects in self irradiated Pu is required to predict the time scale of void swelling and related radiation effects. 1 fig.
Date: November 21, 1996
Creator: Colmenares, C.; Howell, R.H.; Ancheta, D.; Cowan, T.; Hanafee, J. & Sterne, P.
Partner: UNT Libraries Government Documents Department

Ductile damage model with void coalescence

Description: A general model for ductile damage in metals is presented. It includes damage induced by shear stress as well as damage caused by volumetric tension. Spallation is included as a special case. Strain induced damage is also treated. Void nucleation and growth are included and give rise to strain rate effects. Strain rate effects also arise in the model through elastic release wave propagation between damage centers. Underlying physics of the model is the nucleation, growth, and coalescence of voids in a plastically flowing solid. Implementation of the model in hydrocodes is discussed.
Date: March 1, 1995
Creator: Tonks, D.L.
Partner: UNT Libraries Government Documents Department

Vortices in dense self-assembled hole arrays.

Description: We present a study of the upper critical field and pinning strength from the resistivity and magnetization of a Nb film containing a dense array of 45 nm diameter holes on a hexagonal lattice with a spacing of 101 nm. The holes were formed by self-assembly in anodic aluminum oxide (AAO) using an electrochemical procedure. Confinement effects and Little-Parks oscillations are seen above 6 K, and strong pinning with matching field effects is seen below 6 K. Above the first matching field interstitial vortices coexist with vortices trapped in the hole array. Pinning in the Nb films with hole arrays is enhanced by two orders of magnitude over that in continuous Nb films. At low temperature, flux avalanches are observed and imaged using the magneto-optical Faraday effect.
Date: October 9, 2002
Creator: Crabtree, G. W.; Welp, U.; Xiao, Z. L.; Jiang, J. S.; Vlasko-Vlasov, V. K.; Bader, S. D. et al.
Partner: UNT Libraries Government Documents Department

Void morphology in polyethylene/carbon black composites

Description: A combination of small angle neutron scattering (SANS) and contrast matching techniques is used to determine the size and quantity of voids incorporated during fabrication of polyethylene/carbon black composites. The analysis used to extract void morphology from SANS data is based on the three-phase model of microcrack determination via small angle x-rayscattering (SAXS) developed by W.Wu{sup 12} and applied to particulate reinforced composites.
Date: December 31, 1996
Creator: Marr, D.W.M.; Wartenberg, M. & Schwartz, K.B.
Partner: UNT Libraries Government Documents Department

Effect of stoichiometry on defect distribution in cubic GaN grown on GaAs by plasma-assisted MBE

Description: High resolution electron microscopy was used to study the structure of {beta}-GaN epilayers grown on (001) GaAs substrates by plasma- assisted molecular-beam-epitaxy. The rf plasma source was used to promote chemically active nitrogen. The layer quality was shown to depend on growth conditions (Ga flux and N{sub 2} flow for fixed rf power). The best quality of GaN layers was achieved by ``stoichiometric`` growth; Ga-rich layers contain a certain amount of the wurtzite phase. GaN layers contain a high density of stacking faults which drastically decreases toward the GaN surface. Stacking faults are anisotropically distributed in the GaN layer; the majority intersect the interface along lines parallel to the ``major flat`` of the GaAs substrate. This correlates well with the observed anisotropy in the intensity distribution of x-ray reflexions. Formation of stacking faults are often associated with atomic steps at the GaN- GaAs interfaces.
Date: December 31, 1996
Creator: Ruvimov, S.; Liliental-Weber, Z.; Washburn, J.; Drummond, T.J.; Hafish, M. & Lee, S.R.
Partner: UNT Libraries Government Documents Department

Damage evolution and clustering in shock loaded tantalum

Description: Two grades of tantalum were shock loaded by plate impact and recovered. The loading conditions were varied to study the damage evolution in te materials from incipient to full spallation. The authors performed quantitative image analysis and optical profilometry on the recovered specimens. Statistical analyses are shown of the void sizes, void clustering, and void linking in the two material grades.
Date: December 31, 1998
Creator: Thissell, W.R.; Zurek, A.K.; Rivas, J.M.; Tonks, D.L. & Hixson, R.S.
Partner: UNT Libraries Government Documents Department

Quantitative analysis of damage clustering and void linking for spallation modeling in tantalum

Description: In a companion paper in this volume by Zurek et al, micrographs of incipient spallation damage in rolled tantalum were numerically analyzed using image analysis techniques. Void sizes, locations, and overall porosity were measured and tabulated. In this paper, we extend this analysis to include void clusters and examine the correlation between cluster size and the ranges of local instabilities between voids visible in the micrographs. The implications for spallation modeling will be given.
Date: May 1997
Creator: Tonks, D. L.; Zurek, A. K.; Thissell, W. R. & Hixson, R.
Partner: UNT Libraries Government Documents Department

Corrosion resistance of inconel 690 to borax, boric acid, and boron nitride at 1100{degrees}C

Description: Significant general and localized corrosion was observed on Inconel 690 coupons following exposure to borax, boric acid and boron nitride at 1100{degrees}C. Severe localized attack at and below the melt line was observed on coupons exposed to borax. An intergranular attack at and below the melt line was observed on coupons exposed to borax. An intergranular attack (IGA) of the Inconel 690 was also observed. Severe internal void formation and IGA (30 mils penetration after 3 days) was observed in the coupon exposed to boric acid. Both borax and boric acid remove the protective chromium oxide; however, this layer can be reestablished by heating the Inconel 690 to 975 {degrees}C in air for several hours. Inconel 690 in direct contact with boron nitride resulted in the formation of a thick chromium borate layer, a general corrosion rate of 50 to 90 mils per year, and internal void formation of 1 mil per day.
Date: December 12, 1996
Creator: Imrich, K. J.
Partner: UNT Libraries Government Documents Department

Laser intensity modulation by nonabsorbing defects

Description: Nonabsorbing defects can lead to laser damage. Defects such as voids, microcracks, and localized stressed concentrations, even if they differ from the surrounding medium only by refractive index, can serve as positive or negative lenses for the incident laser light. The resulting interference pattern between refracted and diffracted light can result in intensity increases on the order of a factor of 2 some distance away from a typical negative microlens, and even larger for a positive microlens. Thus, the initial damage site can be physically removed from the defect which initiates damage. The parameter that determines the strength of such lensing is (Ka){sup 2}{Delta}{epsilon}, where the wavenumber K is 2{pi}/{lambda}, 2a is the linear size of the defect, and {Delta}{epsilon} is the difference in dielectric coefficient between matrix and scatterer. Thus, even a small change in refractive index results in a significant effect for a defect large compared to a wavelength. Geometry is also important. Three dimensional (e.g. voids) as well as linear and planar (e.g. cracks) microlenses can all have strong effects. This paper evaluates intensification due to spherical voids and high refractive index inclusions.
Date: November 20, 1996
Creator: Feit, M.D., Rubenchik, A.M.
Partner: UNT Libraries Government Documents Department

One-sided infrared thermal imaging for flaw characterization of ceramic matrix composites

Description: One-sided infrared thermal imaging is being used to characterize voids and delamination in SiC/SiC composites. Flaw depth is estimated by examining the decay of surface temperature after application of a thermal pulse. Digital analysis of the surface temperature/time relationship allows characterization of the sizes and positions of defects. Results show that defects of various sizes and depths can be characterized in SiC/SiC composites with the technique.
Date: May 16, 2000
Creator: Deemer, C.; Sun, J. G. & Ellingson, W. A.
Partner: UNT Libraries Government Documents Department

Effect of microvoids on the shock initiation of PETN

Description: We demonstrate that the introduction of microvoids as glass microballoons sensitizes high-density solvent-pressed PETN to shock initiation. At input pressures ranging from 1.4-2.0 GPa, shock propagation velocities are higher and run distances to detonation are shorter for PETN sensitized by microballoons. By selecting the size and density of microballoons, we can therefore study the effect of void size and density on shock initiation by hot spots.
Date: July 1, 1996
Creator: Maienschein, J.L.; Urtiew, P.A.; Garcia, F. & Chandler, J.B.
Partner: UNT Libraries Government Documents Department

Measurement of the DWPF canistered wasteform weight and free volume

Description: The Defense Waste Processing Facility (DWPF) produced a total of fifty-five canistered wasteforms during four campaigns for the Waste Qualification Program to Radioactive Operations. These canistered wasteforms contained borosilicate glasses, which were non-radioactive simulants of the predicted DWPF radioactive glass compositions. Testing of these canisters has been performed as part of a continuing effort to demonstrate compliance with the Waste Acceptance Product Specifications.
Date: June 1, 1996
Creator: Herman, D.T.; Harbour, J.R.; Andrews, M.K. & Cicero, C.A.
Partner: UNT Libraries Government Documents Department

Evidence of melt in {open_quotes}soft{close_quotes} recovered copper jets

Description: A shaped charge (81 mm, 42{degrees}, OFHC copper cone) was fired into a {open_quotes}soft{close_quotes} recovery bunker to allow metallurgical examination of recovered jet particles and the slug. The initial weight of the copper liner was 245 gm, of which 184 gm was recovered. The number of jet particles recovered was 37 (approximately 63% of the particles formed by the charge). Extensive metallurgical analyses were performed on the recovered slug and jet particles. The microstructural features associated with voids, e.g. dendritic grain growth, clearly indicate that the regions in the vicinity of the centerline of the slug and jet particles were melted. In this work we present calculations of jet temperature as a function of constitutive behavior. In order to predict melt in the center region of the jet we find it necessary to scale flow stress with a pressure dependent shear modulus.
Date: August 1, 1995
Creator: Lassila, D.H.; Nikkel, D.J. Jr. & Kershaw, R.P.
Partner: UNT Libraries Government Documents Department

Ductile damage modeling based on void coalescence and percolation theories

Description: A general model for ductile damage in metals is presented. It includes damage induced by shear stress as well as damage caused by volumetric tension. Spallation is included as a special case. Strain induced damage is also treated. Void nucleation and growth are included, and give rise to strain rate effects. Strain rate effects also arise in the model through elastic release wave propagation between damage centers. The underlying physics of the model is the nucleation, growth, and coalescence of voids in a plastically flowing solid. The model is intended for hydrocode based computer simulation. An experimental program is underway to validate the model.
Date: September 1, 1995
Creator: Tonks, D.L.; Zurek, A.K. & Thissell, W.R.
Partner: UNT Libraries Government Documents Department

Techniques for in situ HVEM mechanical deformation of nanostructural materials

Description: We have developed two in-situ HVEM techniques which allow us to begin fundamental investigations into the mechanisms of deformation and fracture in nonstructured materials. A procedure for the observation of tensile deformation and failure in multilayers materials in cross-section is given and also the development of an in-situ HVEM nanoindentor of surfaces and films on surfaces in cross-section.
Date: August 7, 1995
Creator: Wall, M.A.; Barbee, T.W. Jr. & Dahmen, U.
Partner: UNT Libraries Government Documents Department

Using diffusion measurements to determine pore-size distributions in porous materials

Description: A method for determining pore-size distrbutions from diffusion measurements is presented. A Wicke-Kallenbach experiment, for measuring diffusion fluxes within porous materials, was carried out over a significant portion of the transition range between Knudsen flow and bulk diffusion. If the internal porous structure of the material is modeled as myriad nonintersecting cylindrical pores, an equation may be derived for the flux as a function of pressure, in which the flux is a functional of the pore-size distribution. The equation is a Fredholm integral equation of the first kind. This is an application of the general inversion problem, and solution of the equation for the pore-size distribution is possible. It is demonstrated from calculated fluxes using postulated ideal distributions that the method works very well for both unimodal and bimodal distributions. The method is no extraordinarily sensitivire to experimental error. An example of a distribution obtained from a commercial porous catalyst is presented and compared with that obtained by mercury porosimetry.
Date: January 1, 1980
Creator: Brown, L.F. & Travis, B.J.
Partner: UNT Libraries Government Documents Department

Predicting the thermal response of an encapsulation process

Description: An evaluation of the thermal behavior of an electronic component assembly has indicated a need for increasing the temperature-soak time prior to the electrical testing of potted and unpotted assemblies. The preheat time before encapsulation was found adequate, and the internal mold temperature proved to be within desirable limits during encapsulation. Use of the automatic encapsulation system prevents excessive heat loss during the potting operation and provides a 50% savings in time. A movie showing the encapsulation of a nonfunctional unit in a clear container revealed the formation of three types of voids. Corrective action to eliminate the voids is described.
Date: January 1, 1979
Creator: Richardson, J.H.
Partner: UNT Libraries Government Documents Department

[The structural basis for fatigue failure initiation in glassy polymers]. Progress report, July 1991--October 1993

Description: In this period efforts were devoted to studying the microstructural elements characterizing fatigue failure initiation, their evolution as a function of fatigue history, and role of external variables. Materials studied include polycarbonate (PC) and its derivatives with different relaxation behaviors, and epoxies with different cross-link densities. The majority of the studies were devoted to PC. Techniques used included mechanical testing, volumetry, density, DSC, x-ray scattering, positron annihilation, TEM, etc. Results suggest that craze initiation starts with expansion of ``elementary`` voids; that fatigue failure initiation in bulk, amorphous PC is generation of stable voids or ``proto-crazes``; that sizes of initial voids are generally in the range of tens of nanometers; that growth of proto- crazes into mature crazes occurs through expansion of voids and generation of new ones perpendicular to fatigue stress; and that fatigue craze initiation in bulk, amorphous PC even at below T{sub g} may involve disentanglement of polymer chains.
Date: December 31, 1993
Creator: Yee, A. F.
Partner: UNT Libraries Government Documents Department

Fundamental study on transient bubble (slug) behavior by characterizing transient forces of solid particles in fluidized beds. Topical report, January 1991--June 1992

Description: The objective of this work is to recognize and interpret the signals of transient motion of bubbles (slugs) in fluidized beds (METC/DOE) by measuring and utilizing the signals of transient gas phase pressure fluctuation, and also by taking the video pictures of transient motions of the bubbles and emulsion phase in fluidized beds. The two signals were measured simultaneously in a three dimensional fluidized bed. Correlation study on the voidage signal and pressure fluctuation was carried out. A domain concept was introduced and new bubble classification was suggested. A video recording approach was also developed to record the transient bubble motion in a two dimensional fluidized bed with a special consideration. This new approach enhances the understanding of bubble image and the physical meaning of transient particle forces. The fundamental mechanism of bubble flow was experimentally investigated and interesting new findings of the transient bubble flow were obtained.
Date: October 1, 1992
Creator: Kono, H.
Partner: UNT Libraries Government Documents Department

Geometric morphology of cellular solids

Description: We demonstrate how to derive morphological information from micrographs, i.e., grey-level images, of polymeric foams. The segmentation of the images is performed by applying a pulse-coupled neural network. This processing generates blobs of the foams walls/struts and voids, respectively. The contours of the blobs and their corresponding points form the input to a constrained Delaunay tessellation, which provides an unstructured grid of the material under consideration. The subsequently applied Chordal Axis Transform captures the intrinsic shape characteristics, and facilitates the identification and localization of key morphological features. While stochastic features of the polymeric foams struts/walls such as areas, aspect ratios, etc., already can be computed at this stage, the foams voids require further geometric processing. The voids are separated into single foam cells. This shape manipulation leads to a refinement of the initial blob contours, which then requires the repeated application of the constrained Delaunay tessellation and Chordal Axis Transform, respectively. Using minimum enclosing rectangles for each foam cell, finally the stochastic features of the foam voids are computed.
Date: January 1, 2001
Creator: Schlei, B. R. (Bernd R.); Prasad, L. (Lakshaman) & Skourikhine, A. N. (Alexei N.)
Partner: UNT Libraries Government Documents Department