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  • Other Sources  (282)
  • COMPOSITE MATERIALS  (282)
  • 1990-1994  (282)
  • 1991  (282)
  • 1
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    Repair of oxidation protection coatings on carbon-carbon using preceramic polymers (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: The paper describes a field-applicable technique for the repair of damage to SiC protective coatings on carbon/carbon composites, using commercial preceramic polymers, such as perhydropolysilazane developed by the Southwest Research Institute and several commercial polymers (NICALON, PS110, PS116, PS117, NCP-200, and PHPS were tested). After being applied on the damaged panel and oxidized at 1400 C, these polymers form either SiC or Si3N4 (or a mixture of both). It was found that impact damaged carbon/carbon specimens repaired with perhydropolysilazane exhibit substantial oxidation resistance. Many of the other tested preceramic polymer were found to be unsuitable for the purpose of repair due to either low ceramic yield, foaming, or intumescence.
    Keywords: COMPOSITE MATERIALS
    Type: In: Damage and oxidation protection in high temperature composites. Vol. 1; Proceedings of the Symposium, 112th ASME Winter Annual Meeting, Atlanta, GA, Dec. 1-6, 1991 (A93-53937 23-24); p. 131-138.
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  • 2
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    Fatigue life prediction of an intermetallic matrix composite at elevated temperatures (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: A strain-based fatigue life prediction method is proposed for an intermetallic matrix composite (IMC) under tensile cyclic loadings at elevated temperatures. Styled after the 'Universal Slopes' method, the model utilizes the composite's tensile properties to estimate fatigue life. Factors such as fiber volume ratio (Vf), number of plys and temperature dependence are implicitly incorporated into the model through these properties. The model constants are determined by using unidirectional fatigue data at temperatures of 425 and 815 C. Fatigue lives from two independent sources are used to verify the model at temperatures of 650 and 760 C. Cross-ply lives at 760 C are also predicted. It is demonstrated that the correlation between experimental and predicted lives is within a factor of two.
    Keywords: COMPOSITE MATERIALS
    Type: In: Failure mechanisms in high temperature composite materials; Proceedings of the Symposium, 112th ASME Winter Annual Meeting, Atlanta, GA, Dec. 1-6, 1991 (A93-31351 11-24); p. 45-54.
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  • 3
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    Void control in the crystallization of lithium fluoride (1991)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The effect of tungsten-coated graphite fibers on the radiant heat transfer characteristics of salt-fiber composites was studied by measuring the onset of melting as a function of applied furnace power. As the fiber concentration was increased from 0 to 5.40 percent fiber by weight, the furnace temperature required to melt the lithium fluoride also increased. Upon cooling, each of the crystalline salt-fiber composites were cut open with a diamond saw to expose the void. Optical photographs of the voids revealed a trend in void location and size, with the largest void, and the least change in the outer dimension of the boule upon cooling, occurring in the sample with the most fiber.
    Keywords: COMPOSITE MATERIALS
    Type: In: Space nuclear power systems; Proceedings of the 8th Symposium, Albuquerque, NM, Jan. 6-10, 1991. Pt. 1 (A93-13751 03-20); p. 49-54.
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  • 4
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    Delamination behavior of quasi-isotropic graphite epoxy laminates subjected to tension and torsion loads (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: Sixteen and thirty-two ply quasi-isotropic laminates fabricated from AS4/3501-6 were subjected to pure tension, simultaneous tension and torsion, and torsion fatigue. Layups tested were (45 sub n/-45 sub n/0 sub n/90 sub n) sub s, with n = 2 or 4. A torsion damage pattern consisting of a localized matrix crack and delaminations was characterized, and the measured torsional stiffnesses were compared with calculated values. It was found that a combination of tension and torsion led to failure at smaller loads than either type of deformation acting alone. Further work is required to determine the exact form of the failure criterion.
    Keywords: COMPOSITE MATERIALS
    Type: In: AHS National Technical Specialists' Meeting on Rotorcraft Structures, Williamsburg, VA, Oct. 29-31, 1991, Proceedings (A93-27951 10-05); 15 p.
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  • 5
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    Microfracture in high temperature metal matrix crossply laminates (1991)
    In:  Other Sources
    Details
    Publication Date: 2019-08-27
    Description: Microfracture (fiber/matrix fracture, interphase debonding and inter-ply delamination) in high temperature metal matrix composites (HTMMC), subjected to both mechanical and thermal loading, is computationally simulated. A crossply 0.3 fiber volume ratio SiC/Ti15 composite with 0/90/0 layup is evaluated for microfracture using a multicell finite element model. A computational simulation procedure based on strain energy release rates is used to predict the fracture process and establish the hierarchy of fracture modes. Microfracture results for various loading cases are presented and discussed.
    Keywords: COMPOSITE MATERIALS
    Type: In: Failure mechanisms in high temperature composite materials; Proceedings of the Symposium, 112th ASME Winter Annual Meeting, Atlanta, GA, Dec. 1-6, 1991 (A93-31351 11-24); p. 31-36.
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  • 6
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    Impact response of composite materials (1991)
    In:  CASI
    Details
    Publication Date: 2019-07-20
    Description: Composite materials composed of carbon fibers and resin matrices offer great promise in reducing the weight of aerospace structures. However they remain extremely vulnerable to out of plane impact loads, which lead to severe losses in strength and stiffness. The results of an experimental program, undertaken to investigate the low velocity impact damage tolerance of composite materials is presented. The objectives were to identify key neat resin/composite properties that lead to enhancement of composite impact damage tolerance and to find a small scale test that predicts compression after impact properties of panels. Five materials were selected for evaluation. These systems represented different classes of material behavior such as brittle epoxy, modified epoxies, and amorphous and semicrystalling thermoplastics. The influence of fiber properties on the impact performance was also studied in one material, i.e., in polyether ether ketone (PEEK). Several 24 and 48 ply quasi-isotropic and 24 ply orthotropic laminates were examined using an instrumented drop weight impactor. Correlations with post impact compression behavior were made.
    Keywords: COMPOSITE MATERIALS
    Type: NASA-CR-187896 , NAS 1.26:187896
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  • 7
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    Morphology and microstructure of composite materials (1991)
    In:  CASI
    Details
    Publication Date: 2019-07-20
    Description: Lightweight continuous carbon fiber based polymeric composites are currently enjoying increasing acceptance as structural materials capable of replacing metals and alloys in load bearing applications. As with most new materials, these composites are undergoing trials with several competing processing techniques aimed at cost effectively producing void free consolidations with good mechanical properties. As metallic materials have been in use for several centuries, a considerable database exists on their morphology - microstructure; and the interrelationships between structure and properties have been well documented. Numerous studies on composites have established the crucial relationship between microstructure - morphology and properties. The various microstructural and morphological features of composite materials, particularly those accompanying different processing routes, are documented.
    Keywords: COMPOSITE MATERIALS
    Type: NASA-CR-189473 , NAS 1.26:189473
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  • 8
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    Toughening of PMR composites by semi-interpenetrating networks (1991)
    In:  CASI
    Details
    Publication Date: 2019-07-20
    Description: Polymerization of monomer reactants (PMR-15) type polyimide and RP46 prepregs were drum wound using IM-7 fibers. Prepregging and processing conditions were optimized to yield good quality laminates with fiber volume fractions of 60 percent (+/- 2 percent). Samples were fabricated and tested to determine comprehensive engineering properties of both systems. These included 0 deg flexure, short beam shear, transverse flexure and tension, 0 deg tension and compression, intralaminar shear, short block compression, mode 1 and 2 fracture toughness, and compression after impact properties. Semi-2-IPN (interpenetrating polymer networks) toughened PMR-15 and RP46 laminates were also fabricated and tested for the same properties.
    Keywords: COMPOSITE MATERIALS
    Type: NASA-CR-189468 , NAS 1.26:189468
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  • 9
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    Application of a design-build-team approach to low cost and weight composite fuselage structure (1991)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Relationships between manufacturing costs and design details must be understood to promote the application of advanced composite technologies to transport fuselage structures. A team approach, integrating the disciplines responsible for aircraft structural design and manufacturing, was developed to perform cost and weight trade studies for a twenty-foot diameter aft fuselage section. Baseline composite design and manufacturing concepts were selected for large quadrant panels in crown, side, and keel areas of the fuselage section. The associated technical issues were also identified. Detailed evaluation of crown panels indicated the potential for large weight savings and costs competitive with aluminum technology in the 1995 timeframe. Different processes and material forms were selected for the various elements that comprise the fuselage structure. Additional cost and weight savings potential was estimated for future advancements.
    Keywords: COMPOSITE MATERIALS
    Type: NASA-CR-4418 , NAS 1.26:4418
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  • 10
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    Relationship between voids and interlaminar shear strength of polymer matrix composites (1991)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The effect of voids on the interlaminar shear strength of a polyimide matrix composite system is described. The AS4 graphite/PMR-15 composite was chosen for study because this system can be readily processed by using the standard specified cure cycle to produce void-free composites and because preliminary work in this study had shown that the processing parameters of this resin matrix system can be altered to produce cured composites of varying void contents. Thirty-eight 12-ply unidirectional composite panels were fabricated for this study. A significant range of void contents (0 to 10 percent) was produced. The panels were mapped, ultrasonically inspected, and sectioned into interlaminar shear, flexure, and fiber content specimens. The density of each specimen was measured and interlaminar shear and flexure strength measurements were then made. The fiber content was measured last. The results of these tests were evaluated by using ultrasonic results, photomicrographs, statistical methods, theoretical relationships derived by other investigators, and comparison of the test data with the Integrated Composite Analyzer (ICAN) computer program developed at the Lewis Research Center for predicting composite ply properties. The testing is described in as much detail as possible in order to help others make realistic comparisons.
    Keywords: COMPOSITE MATERIALS
    Type: NASA-TM-103643 , E-5825 , NAS 1.15:103643 , International SAMPE Symposium and Exhibition; Apr 15, 1991 - Apr 18, 1991; San Diego, CA; United States
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