New perspectives on the fracture of Nicalon fibers

New perspectives on the fracture of Nicalon fibers

Date: November 1, 1997
Creator: Taylor, S.T.; Lowe, T.C. & Butt, D.P.
Description: Experimental studies have been conducted to examine the strength and fracture behavior of monofiliment Nicalon{sup 3} SiC fibers ranging in diameter from 8 to 22 {mu}m. The effects of varying fiber diameter, flaw location and flaw population on the tensile behavior of individual fibers were investigated using fractography. Results indicate that variations in fiber diameter influence the apparent fiber fracture toughness K{sub 1c}, with higher K{sub 1c} values observed for decreasing fiber diameters. Observations also suggest that the location of the critical flaw may play a role in the fracture of Nicalon fibers. In addition to surface flaws, three distinct internal flaw populations are seen to cause fracture in Nicalon fibers.
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Quantum cryptography over underground optical fibers

Quantum cryptography over underground optical fibers

Date: May 1, 1996
Creator: Hughes, R.J.; Luther, G.G.; Morgan, G.L.; Peterson, C.G. & Simmons, C.
Description: Quantum cryptography is an emerging technology in which two parties may simultaneously generated shared, secret cryptographic key material using the transmission of quantum states of light whose security is based on the inviolability of the laws of quantum mechanics. An adversary can neither successfully tap the key transmissions, nor evade detection, owing to Heisenberg`s uncertainty principle. In this paper the authors describe the theory of quantum cryptography, and the most recent results from their experimental system with which they are generating key material over 14-km of underground optical fiber. These results show that optical-fiber based quantum cryptography could allow secure, real-time key generation over ``open`` multi-km node-to-node optical fiber communications links between secure ``islands.``
Contributing Partner: UNT Libraries Government Documents Department
Some new perspective on the strength and fracture of Nicalon fibers

Some new perspective on the strength and fracture of Nicalon fibers

Date: July 1, 1996
Creator: Taylor, S.T.; Zhu, Y.T.; Butt, D.P.; Stout, M.G.; Blumenthal, W.R. & Lowe, T.C.
Description: Nicalon{trademark} SiC fibers, processed by melt-spinning, are attractive reinforcing materials for high-temperature structural composites. This paper studies the effects of fiber diameter on fracture and statistical strength distribution of the fibers, by means of fractography on 8-22 {mu}m fibers fractured under tensile load. Flaw population and location effects are also studied.
Contributing Partner: UNT Libraries Government Documents Department
Characterization of porous carbon fibers and related materials

Characterization of porous carbon fibers and related materials

Date: July 15, 1996
Creator: Fuller, E.L. Jr.
Description: This program was geared to support the Fossil Energy Material Sciences Program with respect to several areas of interest in efficient production and utilization of energy. Carbon molecular sieves have great potential for economically purifying gases; i.e. removal of carbon dioxide from natural gas without having to resort to cryogenic techniques. Microporous carbons can be tailored to serve as adsorbents for natural gas in on-board storage in automotive applications, avoiding high pressures and heavy storage tanks. This program is a laboratory study to evaluate production methodologies and activation processes to produce porous carbons for specific applications. The Carbon Materials Technology Group of Oak Ridge National Laboratory (ORNL) is engaged in developmental programs to produce activated carbon fibers (ACF) for applications in fixed beds and/or flowing reactors engineering applications.
Contributing Partner: UNT Libraries Government Documents Department
Accurate estimation of the elastic properties of porous fibers

Accurate estimation of the elastic properties of porous fibers

Date: May 1, 1997
Creator: Thissell, W.R.; Zurek, A.K. & Addessio, F.
Description: A procedure is described to calculate polycrystalline anisotropic fiber elastic properties with cylindrical symmetry and porosity. It uses a preferred orientation model (Tome ellipsoidal self-consistent model) for the determination of anisotropic elastic properties for the case of highly oriented carbon fibers. The model predictions, corrected for porosity, are compared to back-calculated fiber elastic properties of an IM6/3501-6 unidirectional composite whose elastic properties have been determined via resonant ultrasound spectroscopy. The Halpin-Tsai equations used to back-calculated fiber elastic properties are found to be inappropriate for anisotropic composite constituents. Modifications are proposed to the Halpin-Tsai equations to expand their applicability to anisotropic reinforcement materials.
Contributing Partner: UNT Libraries Government Documents Department
On the statistical strength of nicalon fibers and its characterization

On the statistical strength of nicalon fibers and its characterization

Date: February 1, 1997
Creator: Zhu, Y.T.; Taylor, S.T.; Stout, M.G.; Butt, D.P.; Blumenthal, W.R. & Lowe, T.C.
Description: Nicalon fibers are one of the most attractive ceramic fibers for reinforcing high temperature structural composites. Experiment show that the diameter variation (from 8 to 22 {mu}m) in a tow of commercial Nicalon fibers has an effect on statistical strength distribution of Nicalon fibers. Therefore, an appropriate characterization of the statistical distribution of fiber strength, capable of accounting for the effect of diameter variation, is required. The two-parameter single-modal Weibull distribution is found inadequate for characterizing the strength of Nicalon fibers. This work demonstrates that a 3-parameter modified Weibull distribution can successfully characterize the strength of Nicalon fibers; this distribution yields a higher {beta} value, which indicates less scatter in fiber strength than with the 2-parameter single modal Weibull distribution. It more accurately treats the strength variation caused by diameter variation. It is also much easier to use than the 4-parameter bimodal. Moreover, it is seen to more accurately treat the strength variation caused by diameter variation than the single modal 2-parameter analysis.
Contributing Partner: UNT Libraries Government Documents Department
Use of neutron-capture plastic fibers for nondestructive assay

Use of neutron-capture plastic fibers for nondestructive assay

Date: December 31, 1998
Creator: Heger, A.S.; Grazioso, R.F.; Mayo, D.R.; Ensslin, N.; Miller, M.C.; Huang, H.Y. et al.
Description: Neutron-capture plastic fibers can be used as a nondestructive assay tool. The detectors consist of an active region assembled from ribbons of boron-({sup 10}B) loaded optical fibers. The mixture of the moderator and thermal neutron absorber in the fiber yields a detector with high efficiency ({var_epsilon}) and a short die-away time ({tau}). The deposited energy of the resultant charged particles is converted to light that is collected by photomultiplier tubes mounted at both ends of the fiber. Thermal neutron coincidence counters (TNCC) made of these fibers can serve to verify fissile materials generated from the nuclear fuel cycle. This type of detector may extend the range of materials now accessible to assay by {sup 3}He detectors. Experiments with single fibers of diameters 0.25, 0.50, and 1.00 mm test their ability to distinguish between the signals generated from neutron interactions and those from gamma rays. These results are compared with those obtained from simulation analyses for the same purpose. Light output and attenuation, neutron detection efficiency, and the signal-to-noise ratios of these fibers have also been investigated. The experimental results for light attenuation and neutron detection efficiency are consistent with the values obtained from simulation studies. A comparison of the performance ...
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The effect of neutron irradiation on silicon carbide fibers

The effect of neutron irradiation on silicon carbide fibers

Date: January 1, 1997
Creator: Newsome, G.A.
Description: Nine types of SiC fiber have been exposed to neutron radiation in the Advanced Test Reactor at 250 C for various lengths of time ranging from 83 to 128 days. The effects of these exposures have been initially determined using scanning electron microscopy. The fibers tested were Nicalon{trademark} CG, Tyranno, Hi-Nicalon{trademark}, Dow Corning SiC, Carborundum SiC, Textron SCS-6, polymethysilane (PMS) derived SiC from the University of Michigan, and two types of MER SiC fiber. This covers a range of fibers from widely used commercial fibers to developmental fibers. Consistent with previous radiation experiments, Nicalon fiber was severely degraded by the neutron irradiation. Similarly, Tyranno suffered severe degradation. The more advanced fibers which approach the composition and properties of SiC performed well under irradiation. Of these, the Carborundum SiC fiber appeared to perform the best. The Hi-Nicalon and Dow Corning Fibers exhibited good general stability, but also appear to have some surface roughening. The MER fibers and the Textron SCS-6 fibers both had carbon cores which adversely influenced the overall stability of the fibers.
Contributing Partner: UNT Libraries Government Documents Department
Dielectric property measurement of zirconia fibers at high temperatures

Dielectric property measurement of zirconia fibers at high temperatures

Date: May 1, 1995
Creator: Vogt, G.J.; Tinga, W.R. & Plovnick, R.H.
Description: Using a self-heating, electronically tunable microwave dielectrometer, the complex dielectric constant of zirconia-based filaments was measured at 915 MHz from 350{degrees} to 1100{degrees}C. This fibrous material cools rapidly to near room temperature within several seconds due to a large surface area to volume ratio. Such rapid sample cooling necessitates the use of a self-heating technique to measure the complex dielectric constant at temperatures up to 1100{degrees}C. Sample temperature was measured with optical fiber thermometry. The effect of sample temperature measurement on data accuracy is discussed.
Contributing Partner: UNT Libraries Government Documents Department
The evaluation of Federal Fabrics-Fibers electrochemical capacitors

The evaluation of Federal Fabrics-Fibers electrochemical capacitors

Date: September 1, 1997
Creator: Wright, R.B. & Murphy, T.C.
Description: The electrochemical capacitor devices described in this report were deliverables from the US Department of Energy-Idaho Operations Office (DOE-ID) as part of the US Department of Energy`s (DOE) High Power Energy Storage Program. The Idaho National Engineering and Environmental Laboratory (INEEL) has the responsibility for technical management, testing, and evaluation of high-power batteries and electrochemical capacitors under this Program. The DOE is currently developing various electrochemical capacitors as candidate power assist devices for the Partnership for a New Generation of Vehicles (PNGV) fast response engine requirement. This contract with Federal Fabrics-Fibers was intended to evaluate the use of their novel Z-axis carbon fiber materials as candidate electrodes for electrochemical capacitors. Deliverables were sent to the INEEL`s Energy Storage Technologies (EST) Laboratory for independent testing and evaluation. This report describes performance testing on four selected devices delivered over a 2-year period. Due to the highly experimental nature of the packages, life cycle testing was not conducted.
Contributing Partner: UNT Libraries Government Documents Department
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