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  • Other Sources  (511)
  • COMPOSITE MATERIALS  (511)
  • 1990-1994  (511)
  • 1993  (229)
  • 1991  (282)
  • 1
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    Repair of oxidation protection coatings on carbon-carbon using preceramic polymers (1991)
    In:  Other Sources
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    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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    Modeling the densification of metal matrix composite monotape (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: We present a first model that enables prediction of the density (and its time evolution) of a monotape lay-up subjected to a hot isostatic or vacuum hot pressing consolidation cycle. Our approach is to break down the complicated (and probabilistic) consolidation problem into simple, analyzable parts and to combine them in a way that correctly represents the statistical aspects of the problem, the change in the problem's interior geometry, and the evolving contributions of the different deformation mechanisms. The model gives two types of output. One is in the form of maps showing the relative density dependence upon pressure, temperature, and time for step function temperature and pressure cycles. They are useful for quickly determining the best place to begin developing an optimized process. The second gives the evolution of density over time for any (arbitrary) applied temperature and pressure cycle. This has promise for refining process cycles and possibly for process control. Examples of the models application are given for Ti3Al + Nb, gamma TiAl, Ti6Al4V, and pure aluminum.
    Keywords: COMPOSITE MATERIALS
    Type: Acta Metallurgica et Materialia (ISSN 0956-7151); 41; 8; p. 2297-2316.
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  • 3
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    Reaction layer formation at the graphite/copper-chromium alloy interface (1993)
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    Publication Date: 2019-08-28
    Description: Sessile drop tests were used to obtain information about copper chromium alloys that suitably wet graphite. Characterization of graphite/copper-chromium alloy interfaces subjected to elevated temperatures were conducted using scanning electron micrography, energy dispersive spectroscopy, Auger electron spectroscopy, and X-ray diffraction analyses. These analyses indicate that during sessile drop tests conducted at 1130 C for one hour, copper alloys containing greater than 0.98 percent chromium form continuous reaction layers of approximately 10 micron thickness. The reaction layers adhere to the graphite surface. The copper wets the reaction layer to form a contact angle of 60 degrees or less. X-ray diffraction results indicate that the reaction layer is chromium carbide. The kinetics of reaction layer formation were modelled in terms of bulk diffusion mechanisms. Reaction layer thickness is controlled initially by the diffusion of Cr out of Cu alloy and later by the diffusion of C through chromium carbide.
    Keywords: COMPOSITE MATERIALS
    Type: Metallurgical Transactions A - Physical Metallurgy and Materials Science (ISSN 0360-2133); 24A; 1; p. 53-60.
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  • 4
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    Transverse flexural tests as a tool for assessing damage to PMR-15 composites from isothermal aging in air at elevated temperatures (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: To date, the effect of thermo-oxidative aging on unidirectional composite mechanical properties has been monitored by the measurement of interlaminar shear strength (ILSS) and either three or four point longitudinal flexural strength (LFS) of the composites being tested. Both results are affected by the fiber-to-matrix bonding, the former being dependent on the shear resistance of the interface and the latter on the degree of load sharing by the fibers through the fiber/matrix interface. Recently, fiber/matrix interfacial bond strengths have been monitored using a transverse flexural strength (TFS) test method. This test method was used to evaluate the effect of fiber surface treatment on the fiber/matrix.
    Keywords: COMPOSITE MATERIALS
    Type: SAMPE Quarterly (ISSN 0036-0821); 24; 2; p. 49-53.
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  • 5
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    On 'large-scale' stable fiber displacement during interfacial failure in metal matrix composites (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Experimental results are presented to show that interfacial failure in sapphire-reinforced niobium is characterized by 'large-scale' (5-15 microns) plasticity-controlled fiber displacements occurring under increasing loads. The results are based on the responses during thin-slice fiber pushout tests wherein the fiber is supported over a hole twice the fiber diameter. The results describe an interfacial failure process that should also occur near fiber ends during pullout when a fiber is well-bonded to a soft, ductile matrix, such that eventual failure occurs by shear within the matrix near the interface.
    Keywords: COMPOSITE MATERIALS
    Type: Scripta Metallurgica et Materialia (ISSN 0956-716X); 28; 12; p. 1583-1588.
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  • 6
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    Fiber pushout and interfacial shear in metal-matrix composites (1993)
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    Publication Date: 2019-08-28
    Description: Recent thin-slice pushout tests have suggested that MMC matrix-fiber interface failure processes depend not only on such intrinsic factors as bond strength and toughness, and matrix plasticity, but such extrinsic factors as specimen configuration, thermally-induced residual stresses, and the mechanics associated with a given test. After detailing the contrasts in fiber-pullout and fiber-pushout mechanics, attention is given to selected aspects of thin-slice fiber pushout behavior illustrative of the physical nature of interfacial shear response and its dependence on both intrinsic and extrinsic factors.
    Keywords: COMPOSITE MATERIALS
    Type: JOM (ISSN 1047-4838); 45; 3; p. 34-37.
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  • 7
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    Using rapid infrared forming to control interfaces in titanium-matrix composites (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Control of the fiber-matrix reaction during composite fabrication is commonly achieved by shortening the processing time, coating the reinforcement with relatively inert materials, or adding alloying elements to retard the reaction. To minimize the processing time, a rapid IR forming (RIF) technique for metal-matrix composite fabrication has been developed. Experiments have shown that the RIF technique is a quick, simple, and low-cost process to fabricate titanium-alloy matrix composites reinforced with either silicon carbide or carbon fibers. Due to short processing times (typically on the order of 1-2 minutes in an inert atmosphere for composites with up to eight-ply reinforcements), the interfacial reaction is limited and well controlled. Composites fabricated by this technique have mechanical properties that are comparable to (in several cases, superior to) those made with conventional diffusion-bonding techniques.
    Keywords: COMPOSITE MATERIALS
    Type: JOM (ISSN 1047-4838); 45; 3; p. 24-27.
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  • 8
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    Fatigue life prediction of an intermetallic matrix composite at elevated temperatures (1991)
    In:  Other Sources
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    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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  • 9
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    Damage development in titanium metal-matrix composites subjected to cyclic loading (1993)
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    Publication Date: 2019-08-28
    Description: Several layups of SCS-6/Ti-15-3 composites were investigated. Fatigue tests were conducted and analyzed for both notched and unnotched specimens at room temperature and elevated temperatures. Thermo-mechanical fatigue results were analyzed. Test results indicated that the stress in the 0 degree fibers is the controlling factor in fatigue life. The static and fatigue strength of these materials is shown to be strongly dependent on the level of residual stresses and the fiber/matrix interfacial strength. Fatigue tests of notched specimens showed that cracks can initiate and grow many fiber spacings in the matrix materials without breaking fibers. Fiber bridging models were applied to characterize the crack growth behavior. The matrix cracks are shown to significantly reduce the residual strength of notched composites. The notch strength of these composites was accurately predicted using a micromechanics based methodology.
    Keywords: COMPOSITE MATERIALS
    Type: Composites (ISSN 0010-4361); 24; 3; p. 187-196.
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  • 10
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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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