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  • 1
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    Electron-radiation effects on the ac and dc electrical properties and unpaired electron densities of three aerospace polymers (1986)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The effects of gigarad-level total absorbed doses from 1-MeV electrons on the post-irradiation alternating-current (ac) and direct-current (dc) electrical properties and the unpaired electron densities have been studied for Kapton, Ultem, and Mylar. The unpaired electron densities (determined from electron paramagnetic resonance spectroscopy) and the dc electrical conductivities of the irradiated materials were monitored as functions of time following the exposures to determine their decay characteristics at room temperature. The elevated-temperature ac electrical dissipations of the Ultem and Mylar were affected by the radiation. The dc conductivity of the Kapton increased by five orders of magnitude, while the dc conductivities of the Ultem and Mylar increased by less than an order of magnitude, due to the radiation. The observed radiation-generated changes in the ac electrical dissipations are explained in terms of known radiation-generated changes in the molecular structures of the three materials. A preliminary model relating the dc electrical conductivity and the unpaired electron density in the Kapton is proposed.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: IEEE Transactions on Nuclear Science (ISSN 0018-9499); NS-33; 1390-139
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  • 2
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    Effects of postcuring on mechanical properties of pultruded fiber-reinforced epoxy composites and the neat resin (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The effects of postcuring on mechanical properties of pultruded fiber-reinforced epoxy-resin composites have been investigated. Composites with carbon, glass, and aramid reinforcement fibers were individually studied. The epoxy was a commercially-available resin that was especially developed for pultrusion fabrication. The pultrusions were conducted at 400 F with postcures at 400, 450, 500, and 550 F. Measurements of the flexural, shear, and interlaminar fracture-toughness properties showed that significant postcuring can occur during the pultrusion process. All three mechanical properties were degraded by the higher (500 and 550 F) temperatures; photomicrographs suggest that the degradation was caused at the fiber-resin interface for all three fiber types.
    Keywords: COMPOSITE MATERIALS
    Type: SAMPE Quarterly (ISSN 0036-0821); 20; 9-16
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  • 3
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    Radio-frequency electrical properties of some neat and metal-doped polyimides (1985)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: As the size and complexity of aerospace systems increase, the uses of polymers are also expected to increase. Polyimides constitute one promising generic class of polymeric materials. They retain good mechanical and physical properties at higher temperatures and absorb less moisture than do the epoxies, which are the polymers most frequently used in present aerospace systems. The properties of these polyimide materials are, therefore, of considerable interest to the aerospace community. Of particular importance are the electrical properties because these properties relate to both electrical and structural applications.
    Keywords: NONMETALLIC MATERIALS
    Type: Studies of Molecular Properties of Polymeric Materials: Aerospace Environmental Effects on Three Linear Polymers; p 35-36
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  • 4
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    Spectroscopic comparison of effects of electron radiation on mechanical properties of two polyimides (1987)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The differences in the radiation durabilities of two polyimide materials, Du Pont Kapton and General Electric Ultem, are compared. An explanation of the basic mechanisms which occur during exposure to electron radiation from analyses of infrared (IR) and electron paramagnetic resonance (EPR) spectroscopic data for each material is provided. The molecular model for Kapton was, in part, established from earlier modeling for Ultem (pp. 1293-1298 of IEEE Transactions on Nuclear Science, December 1984). Techniques for understanding the durability of one complex polymer based on the understanding of a different and equally complex polymer are demonstrated. The spectroscopic data showed that the primary radiation-generated change in the tensile properties of Ultem (a large reduction in tensile elongation) was due to crosslinking, which followed the capture by phenyl radicals of hydrogen atoms removed from gem-dimethyl groups. In contrast, the tensile properties of Kapton remained unchanged because radical-radical recombination, a self-mending process, took place.
    Keywords: CHEMISTRY AND MATERIALS (GENERAL)
    Type: NASA-TP-2663 , L-16200 , NAS 1.60:2663
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  • 5
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    Absorbed dose thresholds and absorbed dose rate limitations for studies of electron radiation effects on polyetherimides (1989)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The threshold values of total absorbed dose for causing changes in tensile properties of a polyetherimide film and the limitations of the absorbed dose rate for accelerated-exposure evaluation of the effects of electron radiation in geosynchronous orbit were studied. Total absorbed doses from 1 kGy to 100 MGy and absorbed dose rates from 0.01 MGy/hr to 100 MGy/hr were investigated, where 1 Gy equals 100 rads. Total doses less than 2.5 MGy did not significantly change the tensile properties of the film whereas doses higher than 2.5 MGy significantly reduced elongation-to-failure. There was no measurable effect of the dose rate on the tensile properties for accelerated electron exposures.
    Keywords: NONMETALLIC MATERIALS
    Type: NASA-TP-2928 , L-16585 , NAS 1.60:2928
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  • 6
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    Spectroscopic analysis of radiation-generated changes in tensile properties of a polyetherimide film (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The effects of electron radiation on Ultem, a polyetherimide were studied for doses from 2 x 10 to the 9th power to 6 x 10 to the 9th power rad. Specimens were studied for tensile property testing and for electron paramagnetic resonance and infrared spectroscopic measurements of molecular structure. A Faraday cup design and a method for remote temperature measurement were developed. The spectroscopic data show that radiation caused dehydrogenation of methyl groups, rupture of main-chain ether linkage, and opening of imide rings, all to form radicals and indicate that the so-formed atomic hydrogen attached to phenyl radicals, but not to phenoxyl radicals, which would have formed hydroxyls. The observed decays of the radiation-generated phenoxyl, gem-dimethyl, and carbonyl radicals were interpreted as a combining of the radicals to form crosslinking. This crosslinking is the probable cause of the major reduction in the elongation of the tensile specimens after irradiation. Subsequent classical solubility tests indicate that the irradiation caused massive crosslinking.
    Keywords: COMPOSITE MATERIALS
    Type: NASA-TP-2429 , L-15873 , NAS 1.60:2429
    Format: application/pdf
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  • 7
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    Studies of molecular properties of polymeric materials: Aerospace environmental effects on three linear polymers (1985)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The development of crystal handling techniques for reflection infrared spectroscopy and methods for the fabrication and testing of tensile specimens are discussed. Data from mechanical, ac and dc electrical, and electron paramagnetic resonance studies conducted to determine the effects of 0.1-MeV and 1.0-MeV electron radiation on Mylar, Kapton, Ultem, and metal-doped Ultem are presented. Total doses ranging from 1 X 10 to the 8 rads to 1 X 10 to the 10 rads and dose rates from 5 X 10 to the 7 rads/hr to 1 X 10 to the 9 rads/hr were employed. The results of a study on the effects of aircraft service-environment fluids on Ultem are also reported. The weights and mechanical properties of Ultem were evaluated before and after exposure to water, JP4, Skydrol, an antifreeze, and a paint stripper.
    Keywords: NONMETALLIC MATERIALS
    Type: NASA-TM-87532 , NAS 1.15:87532
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  • 8
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    Mechanism of electrical conductivity in an irradiated polyimide (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: A polyimide was exposed to 1.0 MeV electron radiation. The radiation-induced radical density and dc conductivity were measured at various post-irradiation times. The radiation-induced radical density was found to be correlated to the increased dc conductivity through a hopping model of conductivity. The post-irradiation radical species were identified.
    Keywords: NONMETALLIC MATERIALS
    Type: Journal of Physics and Chemistry of Solids (ISSN 0022-3697); 50; 7 19
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  • 9
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    Probability distribution of wind retrieval error for the NASA scatterometer (1989)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The NASA scatterometer (NSCAT) is a spaceborne scatterometer scheduled to be deployed in the mid-1990s. An analysis of the wind retrieval error distribution for wind estimates based on backscatter measurements made by the NSCAT instrument is presented. The results are based on an end-to-end simulation of the scatterometer instrument and data processing. In general, the distribution of the wind speed error, when normalized, is independent of the true wind speed and direction. The wind speed error can be characterized by a normal distribution. The wind direction error is independent of the true wind speed, but depends on the true wind direction. Details for wind vectors with true wind speeds from 3 m/s to 33 m/s and true wind directions from 0 to 360 deg are presented.
    Keywords: METEOROLOGY AND CLIMATOLOGY
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  • 10
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    Results of a study on polarization mix selection for the NSCAT scatterometer (1989)
    In:  Other Sources
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    Publication Date: 2011-08-19
    Description: The NASA scatterometer (NSCAT) is an instrument designed to measure the radar backscatter of the ocean's surface for estimating the near-surface wind velocity. A given resolution element is observed from several different azimuth angles. From these measurements the near-surface vector wind over the ocean may be inferred using a geophysical model function relating the normalized radar backscatter coefficient (sigma0) to the near-surface wind. The results of a study to select a polarization mix for NSCAT using an end-to-end simulation of the NSCAT scatterometer and ground processing of the sigma0 measurements into unambiguous wind fields using a median-filter-based ambiguity-removal algorithm are presented. The system simulation was used to compare the wind measurement accuracy and ambiguity removal skill over a set of realistic mesoscale wind fields for various polarization mixes. Considerations in the analysis and simulation are discussed, and a recommended polarization mix is given.
    Keywords: SPACECRAFT INSTRUMENTATION
    Format: text
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