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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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    NASA TECHNICAL REPORTS
  • 2
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    Effects of intermediate-energy electrons on mechanical and molecular properties of a polyetherimide (1984)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: An experiment, using 100-keV electrons and 10 to the 9th -rad doses, was conducted on Ultem polyetherimide film. Mechanical, electron paramagnetic resonance, and infrared spectroscopic data suggested that the radiation produced crosslinking and embrittlement of the material.
    Keywords: NONMETALLIC MATERIALS
    Type: IEEE Transactions on Nuclear Science (ISSN 0018-9499); NS-31; 1293-129
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    NASA TECHNICAL REPORTS
  • 3
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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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    NASA TECHNICAL REPORTS
  • 4
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    Radio-frequency electrical properties of some neat and metal-doped polyimides (1985)
    In:  Other Sources
    Details
    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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  • 5
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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
    Format: application/pdf
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  • 6
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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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  • 7
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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
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  • 8
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    Studies of molecular properties of polymeric materials (1990)
    In:  CASI
    Details
    Publication Date: 2019-07-20
    Description: Aerospace environment effects (high energy electrons, thermal cycling, atomic oxygen, and aircraft fluids) on polymeric and composite materials considered for structural use in spacecraft and advanced aircraft are examined. These materials include Mylar, Ultem, and Kapton. In addition to providing information on the behavior of the materials, attempts are made to relate the measurements to the molecular processes occurring in the material. A summary and overview of the technical aspects are given along with a list of the papers that resulted from the studies. The actual papers are included in the appendices and a glossary of technical terms and definitions is included in the front matter.
    Keywords: NONMETALLIC MATERIALS
    Type: NASA-TM-101854 , NAS 1.15:101854 , PTR-90-3
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    NASA TECHNICAL REPORTS
  • 9
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    The visual acuity in viewing scaled objects on television compared with that in direct viewing (1969)
    In:  CASI
    Details
    Publication Date: 2019-06-27
    Description: Visual acuity for scaled objects by direct viewing and on television monitors
    Keywords: BIOSCIENCES
    Type: NASA-TN-D-5534
    Format: application/pdf
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  • 10
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    Effects Of Irradiation By Electrons On Two Polyimides (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Polyimides of new class, known as polyetherimides, used for composites and castings. Study undertaken to compare effects of electron radiation, in doses expected for 30-year missions in geosynchronous orbit, on molecular structures and tensile properties of two commercially available polyimides: polypyromellitimide and polyetherimide. Findings helpful in development of new polymers that endure radiation, leading to synthesis of polymers not having methyl groups or other moieties that are sources of hydrogen, inhibiting self-mending. Significance of study for polymer industry relating to structures in outer space considerable.
    Keywords: MATERIALS
    Type: LAR-14309 , NASA Tech Briefs (ISSN 0145-319X); 16; 10; P. 72
    Format: text
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