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  • Other Sources  (5)
  • 1990-1994  (5)
  • 1960-1964
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  • 1
    facet.materialart.
    Unknown
    Morphological characterization of selected balloon films and its effects on balloon performances (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Morphological characterization of several polyethylene balloon films have been studied using various techniques. The objective is to determine, if any, differentiating structural or morphological features that can be related to the performance of these balloon film materials. The results of the study indicate that the films are composed of either linear low denstiy polyethylene (LLDPE) or low density polyethylene (LDPE). A selective examination of these data imply that films limited degree of branching and larger crystallites size (same % crystallinity) showed good mechanical properties that appear to correlate with their high level of success in balloon flights.
    Keywords: NONMETALLIC MATERIALS
    Type: Advances in Space Research (ISSN 0273-1177); 14; 2; p. (2)31-(2)34
    Format: text
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    NASA TECHNICAL REPORTS
  • 2
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    Unknown
    Characterization of path effects on the properties of balloon films (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-01-25
    Description: The effect of stress and temperature path on the mechanical properties of a balloon film material (Astrofilm E2) have been studied using two techniques. The first technique is based on uniaxial tensile measurements of prestrained strips of the film as a function of temperature. Data are analyzed in terms of two temperature coefficients, defined here as a stiffness coefficient and a strength coefficient; and by comparing the areas under the stress-strain curves. The second technique investigated the effect of stress and temperature path on inflated cylinders of the same material. The changes in the mechanical properties due to preconditioning in the biaxial stress state were evaluated using the ball burst test. Preliminary findings indicate that the material is stress and temperature path dependent. Changes in stiffness coefficient, draw strength and toughness were measured and discussed. The above techniques may be suitable to document path dependent changes, and to discriminate among films of different manufacture.
    Keywords: NONMETALLIC MATERIALS
    Type: Advances in Space Research (ISSN 0273-1177); 14; 2; p. (2)27-(2)30
    Format: text
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    NASA TECHNICAL REPORTS
  • 3
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    Unknown
    Electron reversal ionizer for detection of trace species using a spherical cathode (1994)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: A reversal electron, high-current ionizer capable of focusing a beam of electrons to a reversal region employs an indirectly heated cathode having a concave emitting surface of width of W less than 2r, where r is the radius of curvature and preferably a ratio of width to radius approximately equal to one for optimum high current for a given cathode width.
    Keywords: ATOMIC AND MOLECULAR PHYSICS
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Unknown
    Laser damage of HR, AR-coatings, monolayers and bare surfaces at 1064 nm (1993)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Laser induced damage thresholds and morphologies were investigated in a variety of uncoated and coated surfaces, including monolayers and multi-layers of different chemical compositions. Both antireflective (AR) and highly reflective (HR) were tested. Testing was done at 1064 nm with 25 picosecond and 8 nanosecond YAG/Nd laser single pulses. Spot diameter in the experiments varied from 0.09 to 0.22 mm. The laser damage measurement procedure consisted of 1-on-1 (single laser pulse in the selected site) and N-on-1 experiments including repeated irradiation by pulses of the same fluence and subsequently raised from pulse to pulse fluence until damage occurred. The highest picosecond damage thresholds of commercially available coatings averaged 12 - 14 J/sq cm, 50 percent less than thresholds obtained in bare fused silica. Some coatings and bare surfaces revealed a palpable preconditioning effect (an increase in threshold of 1.2 to 1.8 times). Picosecond and nanosecond data were compared to draw conclusions about pulse width dependence. An attempt was made to classify damage morphologies according to the type of coating, class of irradiating, and damage level.
    Keywords: LASERS AND MASERS
    Type: NASA-CR-192156 , NAS 1.26:192156
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  • 5
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    Unknown
    An assessment on the validity of toughness as a balloon film discriminator (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Uniaxial and ball burst toughness for eight commercial polyethylene balloon films have been investigated and compared. Uniaxial toughness was measured in both machine and transverse directions using a rectangular sample 25.4 mm wide by 50.8 mm gage length with an average nominal thickness of 20.32 microns (0.8 mils). Ball burst toughness was measured using a ball burst test fixture with 127 mm hole diameter and 50.8 mm ball diameter resulting in a 0.4 ball to hole diameter ratio. Both the size and shape of the deformed area were observed and the ball burst toughness was calculated based on the deformed area of the film instead of the full area. Specimens were tested at 23 C and -80 C and cross head speed was maintained at 508 mm per minute. The uniaxial toughness were in general, higher than the ball burst toughness. The toughness of the films varied from 12 to 365 MPa when measured uniaxially and from 24 to 73 MPa when measured in the ball burst test. Further investigation showed an apparent correlation between film performance in flight as measured by its stress index and its toughness.
    Keywords: NONMETALLIC MATERIALS
    Type: AIAA PAPER 91-3662 , AIAA International Balloon Technology Conference; Oct 08, 1991 - Oct 10, 1991; Albuquerque, NM; United States
    Format: text
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    NASA TECHNICAL REPORTS
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