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  • Other Sources  (56)
  • COMPOSITE MATERIALS  (56)
  • 1990-1994
  • 1985-1989  (56)
  • 1935-1939
  • 1985  (56)
  • 1
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    Shear strain anomalies in composite beam specimens by moire interferometry (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Experimental analyses were performed for determination of in-plane deformations and shear strains in unidirectional and quasi-isotropic graphite-epoxy beams. Forty-eight-ply beams were subjected to five-point and three-point flexure. Whole-field measurements were recorded at load levels from about 20 percent to more than 90 percent of failure loads. Contour maps of U and W displacement fields were obtained by moire interferometry, using reference gratings of 2400 lines/mm. Clearly defined fringes with fringe orders exceeding 1000 were obtained. Whole-field contour maps of shear strains were obtained. Various anomalous effects were detected in the displacement fields. Their analysis indicated excess shear strains in resin-rich zones in regions of shear tractions; free-edge shear strains in quasi-isotropic specimens in regions of normal stresses, and shear stresses associated with cyclic shear compliances of quasi-isotropic laminates in regions of shear tractions. Their contributions could occur independently or in superposition. Qualitative analyses addressed questions of the effect of specimen overhang, nonlinearity, and characteristics of five-point and three-point flexure tests.
    Keywords: COMPOSITE MATERIALS
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  • 2
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    Nondestructive evaluation of composites by optical time domain reflectometry (1985)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: Results in the measurement of slowly varying mechanical loading functions on composites using optical time domain reflectometry (OTDR) in imbedded optical fiber during both simulated manufacture and use are reviewed. First, the basic theoretical and experimental principles of the OTDR system are described. Next, the mechanical system of the composite and the imbedded fiber is analyzed. Results of measurement obtained for various loading functions applied to material specimens are then described and system limitations on spatial resolution, strain amplitude sensitivity, and frequency response are explained in terms of the range and resolution limits of the OTDR system.
    Keywords: COMPOSITE MATERIALS
    Type: Proceedings of the 2nd Annual Review of the Center for Composite Materials and Structures; 15 p
    Format: text
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  • 3
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    Composite materials for space structures (1985)
    In:  CASI
    Details
    Publication Date: 2006-02-14
    Description: The use of advanced composites for space structures is reviewed. Barriers likely to limit further applications of composites are discussed and highlights of research to improve composites are presented. Developments in composites technology which could impact spacecraft systems are reviewed to identify technology needs and opportunities.
    Keywords: COMPOSITE MATERIALS
    Type: ESA Proceedings of 3rd European Symposium on Spacecraft Materials in Space Environments; p 9-21
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  • 4
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    SEM/XPS analysis of fractured adhesively bonded graphite fibre-reinforced polyimide composites (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The surfaces of the graphite fiber-reinforced polyimide composites presently pretreated prior to bonding with polyimide adhesive contained variable amounts of a fluoropolymer, as determined by X-ray photoelectron spectroscopy. Lap shear strengths were determined for unaged samples and for those aged over 500- and 1000-hour periods at 177 and 232 C. Unaged sample lap strengths, which were the highest obtained, exhibited no variation with surface pretreatment, but a significant decrease is noted with increasing aging temperature. These thermally aged samples, however, had increased surface fluorine concentration, while a minimal concentration was found in unaged samples. SEM demonstrated a progressive shift from cohesive to adhesive failure for elevated temperature-aged composites.
    Keywords: COMPOSITE MATERIALS
    Type: Composites (ISSN 0010-4361); 16; 207-219
    Format: text
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  • 5
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    Fractography of the interlaminar fracture of carbon-fibre epoxy composites (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: The failed surfaces of interlaminar fracture (mode I) specimens of AS4/3501-6 were examined using scanning electron microscopy. The principal fracture features were fiber pull-out (bundles and single fibers), hackle markings, and regions of smooth resin fracture. Considerable (30 to 50 percent) relaxation of the deformed resin occurred when the specimens were heated above the matrix glass transition temperature. This relaxation was taken as evidence of extensive shear yielding of the resin during the fracture process. Some of the fractography features are discussed in terms of transverse tensile stresses and peeling stresses acting on the fibers. In some instances these localized stresses focus failure close to the resin-fiber interface, which can be mistakenly interpreted as interfacial failure and low fiber-resin adhesion.
    Keywords: COMPOSITE MATERIALS
    Type: Journal of Materials Science (ISSN 0022-2461); 20; 3184-319
    Format: text
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  • 6
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    Characterization of the thermal conductivity for fibrous refractory composite insulations (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Thermal conductivity for a family of fibrous, refractory composite insulations are characterized through the use of an engineering model and arc-jet data. The model defines the composite as a uniform pore material using measured physical and mechanical properties. Efficiency parameters assigned to the solid and radiation conduction terms in the thermal conductivity equation were found to be dependent only on solid volume fraction and porosity.
    Keywords: COMPOSITE MATERIALS
    Type: Ceramic Engineering and Science Proceedings (ISSN 0196-6219); 6; 769-792
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  • 7
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    Options for improving rigidized ceramic heatshields (1985)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: Studies regarding capabilities, tensile strength, and dimensional stability of fibrous ceramics, used in current thermal protection systems and those required for future NASA advanced transfer vehicles, are presented. It is shown that the use of smaller diameter (2-4 micron) aluminoborosilicate fibers (instead of conventional 11-micron size) in the FRCI composites improves the homogeneity and tensile strength of high-silica composite. Substitution of the smaller aluminoborosilicate fibers by 2-4-micron alumina fibers in the AETB composites improves the dimensional stability, at the expense of a substantial increase in the thermal expansion coefficient, with a potential decrease in tensile strength.
    Keywords: COMPOSITE MATERIALS
    Type: Ceramic Engineering and Science Proceedings (ISSN 0196-6219); 6; 757-768
    Format: text
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  • 8
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    Thermally induced stresses and deformations in layered composite tubes (1985)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The thermally induced stresses and deformations in layered, orthotropic tubes are studied. The motivation for studying tubes is their likely application for use in space structures. Tubes are a strong candidate for this application because of their high structural efficiency, as measured by stiffness per unit weight, and their relative ease of fabrication. Also, tubes have no free edges to deteriorate or delaminate. An anticipated thermal condition for tubes in space is a circumferential temperature gradient. This type of gradient will introduce dimensional changes into the structure and may cause stresses large enough to cause damage to the material. There are potentially large differences in temperatures at different circumferential locations on the tube. Because of this, the effects of temperature dependent material properties on the stresses and deformations may be important. The study is composed of three parts: experiments to determine the functional form of the circumferential gradient and to measure tube deflections; an elasticity solution to compute the stresses and deformations; and an approximate approach to determine the effects of temperature dependent material properties.
    Keywords: COMPOSITE MATERIALS
    Type: Virginia Polytechnic Inst. and State Univ. Proceedings of the 2nd Annual Review of the Center for Composite Materials and Structures; 37 p
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  • 9
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    Iosipescu shear properties of graphite fabric/epoxy composite laminates (1985)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The Iosipescu shear test method is used to measure the in-plane and interlaminar shear properties of four T300 graphite fabric/934 epoxy composite materials. Different weave geometries tested include an Oxford weave, a 5-harness satin weave, an 8-harness satin weave, and a plain weave with auxiliary warp yarns. Both orthogonal and quasi-isotropic layup laminates were tested. In-plane and interlaminar shear properties are obtained for laminates of all four fabric types. Overall, little difference in shear properties attributable to the fabric weave pattern is observed. The auxiliary warp material is significantly weaker and less stiff in interlaminar shear parallel to its fill direction. A conventional strain gage extensometer is modified to measure shear strains for use with the Iosipescu shear test. While preliminary results are encouraging, several design iterations failed to produce a reliable shear transducer prototype. Strain gages are still the most reliable shear strain transducers for use with this test method.
    Keywords: COMPOSITE MATERIALS
    Type: NASA-CR-176316 , NAS 1.26:176316 , UWME-DR-501-103-1
    Format: application/pdf
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  • 10
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    Effects of high energy radiation on the mechanical properties of epoxy-graphite fiber reinforced composites (1985)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: In an effort to elucidate the changes in molecular structural and mechanical properties of epoxy/graphite fiber composites upon exposure to ionizing radiation in a simulated space environment, spectroscopic and surface properties of tetraglycidyl-4,4'-diamino diphenyl methane (TGDDM) red with diamino diphenyl sulfone (DDS) and T-300 graphite fiber were investigated following exposure to ionizing radiation. Cobalt-60 gamma radiation and 1/2 MeV electrons were used as radiation sources. The system was studied using electron spin resonance (ESR) spectroscopy, infrared absorption spectroscopy, contact angle measurements, and electron spectroscopy for chemical analysis.
    Keywords: COMPOSITE MATERIALS
    Type: NASA-CR-176487 , NAS 1.26:176487
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