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  • Other Sources  (1,199)
  • COMPOSITE MATERIALS  (1,199)
  • 1990-1994  (1,199)
  • 1
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    Transverse shear stresses and their sensitivity coefficients in multilayered composite panels (1994)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: A computational procedure is presented for the accurate determination of transverse shear stresses and their sensitivity coefficients in flat multilayered composite panels subjected to mechanical and thermal loads. The sensitivity coefficients measure the sensitivity of the transverse shear stresses to variations in the different lamination and material parameters of the panel. The panel is discretized by using either a three-field mixed finite element model based on a two-dimensional first- order shear deformation plate theory or a two-field degenerate solid element with each of the displacement components having a linear variation throughout the thickness of the laminate. The evaluation of transverse shear stresses can be conveniently divided into two phases. The first phase consists of using a superconvergent recovery technique for evaluating the in-plane stresses in the different layers. In the second phase, the transverse shear stresses are evaluated by using piecewise integration, in the thickness direction, of the three-dimensional equilibrium equations. The same procedure is used for evaluating the sensitivity coefficients of the transverse shear stresses. The effectiveness of the computational procedure is demonstrated by means of numerical examples of multilayered cross-ply panels subjected to transverse loading, uniform temperature change, and uniform temperature gradient through the thickness of the panel. In each case the standard of the comparison is taken to be the exact solution of the three dimensional thermoelasticity equations of the panel.
    Keywords: COMPOSITE MATERIALS
    Type: AIAA Journal (ISSN 0001-1452); 32; 6; p. 1259-1269
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  • 2
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    Repair of oxidation protection coatings on carbon-carbon using preceramic polymers (1991)
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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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  • 3
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    Approaches to polymer-derived CMC matrices (1992)
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    Publication Date: 2019-08-28
    Description: The use of polymeric precursors to ceramics permits the fabrication of large, complex-shaped ceramic matrix composites (CMC's) at temperatures which do not degrade the fiber. Processing equipment and techniques readily available in the resin matrix composite industry can be adapted for CMC fabrication using this approach. Criteria which influence the choice of candidate precursor polymers, the use of fillers, and the role of fiber architecture and ply layup are discussed. Three polymer systems, polycarbosilanes, polysilazanes, and polysilsesquioxanes, are compared as candidate ceramic matrix precursors.
    Keywords: COMPOSITE MATERIALS
    Type: In: International SAMPE Technical Conference, 24th and International SAMPE Metals and Metals Processing Conference, 3rd, Toronto, Canada, Oct. 20-22, 1992, Proceedings. Vol. 24 (A93-53376 23-23); p. T950-T961.
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  • 4
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    Modeling the densification of metal matrix composite monotape (1993)
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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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  • 5
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    Composite materials for structures on planetary surfaces (1992)
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    Publication Date: 2019-08-28
    Description: The physical and mechanical properties of advanced composite materials as related to their use in structures on planetary surfaces are reviewed. Polymer matrix composites are recommended as the best materials in the first exploration stages. Achievement of mechanical properties, physical properties, improved processability, and ease of assembly required on planetary surfaces depends on the tailorability of composites.
    Keywords: COMPOSITE MATERIALS
    Type: In: Engineering, construction, and operations in space III: Space '92; Proceedings of the 3rd International Conference, Denver, CO, May 31-June 4, 1992. Vol. 2 (A93-41976 17-12); p. 1297-1308.
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  • 6
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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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  • 7
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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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  • 8
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    Prediction of matrix fatigue crack initiation in notched SCS-6/Ti-15-3 metal matrix composites (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Several lay-ups of SCS-6/Ti-15-3 metal matrix composites were tested in either a center hole or a double edge notched geometry. At different cyclic stress levels, the number of cycles required to develop matrix fatigue cracks at the notches was recorded. A fatigue strat-life curve was developed for the Ti-15-3 matrix material. This modified parameter predicted the number of cycles required for matrix crack initiation at the notches. The predictions were in good agreement with the experimental data.
    Keywords: COMPOSITE MATERIALS
    Type: Journal of Composites Technology & Research (ISSN 0885-6804); 14; 4; p. 221-224.
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  • 9
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    Creep behavior of tungsten fiber reinforced niobium metal matrix composites (1992)
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    Publication Date: 2019-08-28
    Description: Tungsten fiber reinforced niobium metal matrix composites were evaluated for use in space nuclear power conversion systems. The composite panels were fabricated using the arc-spray monotape technique at the NASA Lewis Research Center. The creep behavior of W/Nb composite material was determined at 1400 and 1500 K in vacuum over a wide range of applied loads. The time to reach 1 percent strain, the time to rupture, and the minimum creep rate were measured. The W/Nb composites exceeded the properties of monolithic niobium alloys significantly even when compared creep strength also was evaluated. Kirkendall void formation was observed at the fiber/matrix interface; the void distribution differed depending the fiber orientation relative to the stress axis. A relationship was found between the fiber orientation and the creep strength.
    Keywords: COMPOSITE MATERIALS
    Type: In: Space nuclear power systems 1989; Proceedings of the 6th Symposium, Albuquerque, NM, Jan. 8-12, 1989. Vol. 1 (A93-20752 06-20); p. 53-60.
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  • 10
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    On 'large-scale' stable fiber displacement during interfacial failure in metal matrix composites (1993)
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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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