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  • Other Sources  (229)
  • COMPOSITE MATERIALS  (229)
  • 1990-1994  (229)
  • 1993  (229)
  • 1
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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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  • 2
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    Reaction layer formation at the graphite/copper-chromium alloy interface (1993)
    In:  Other Sources
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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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  • 3
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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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  • 4
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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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  • 5
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    Fiber pushout and interfacial shear in metal-matrix composites (1993)
    In:  Other Sources
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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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  • 6
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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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  • 7
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    Damage development in titanium metal-matrix composites subjected to cyclic loading (1993)
    In:  Other Sources
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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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  • 8
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    TiC growth in C fiber/Ti alloy composites during liquid infiltration (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: A cylindrical model is developed for predicting the reaction zone thickness of carbon fiber-reinforced Ti-matrix composites, and good agreement is obtained between its predicted values and experimental results. The reaction-rate constant for TiC formation is estimated to be 1.5 x 10 exp -9 sq cm/sec. The model is extended to evaluate the relationship between C-coating thicknesses on SiC fibers and processing times.
    Keywords: COMPOSITE MATERIALS
    Type: Scripta Metallurgica et Materialia (ISSN 0956-716X); 29; 2; p. 147-152.
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  • 9
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    Thermal conductivity and thermal expansion of graphite fiber-reinforced copper matrix composites (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The high specific conductivity of graphite fiber/copper matrix (Gr/Cu) composites offers great potential for high heat flux structures operating at elevated temperatures. To determine the feasibility of applying Gr/Cu composites to high heat flux structures, composite plates were fabricated using unidirectional and cross-plied pitch-based P100 graphite fibers in a pure copper matrix. Thermal conductivity of the composites was measured from room temperature to 1073 K, and thermal expansion was measured from room temperature to 1050 K. The longitudinal thermal conductivity, parallel to the fiber direction, was comparable to pure copper. The transverse thermal conductivity, normal to the fiber direction, was less than that of pure copper and decreased with increasing fiber content. The longitudinal thermal expansion decreased with increasing fiber content. The transverse thermal expansion was greater than pure copper and nearly independent of fiber content.
    Keywords: COMPOSITE MATERIALS
    Type: Metallurgical Transactions A - Physical Metallurgy and Materials Science (ISSN 0360-2133); 24A; 1; p. 43-52.
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  • 10
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    Interfacial reactions in titanium/SCS fiber composites during fabrication (1993)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: The objectrive of the study was to determine the effect of titanium concentration and different pyrocarbon fiber coatings on the morphology and the extent of fiber-matrix reactions in Ti/SiC composites fabricated by rapid infrared forming (RIF). It is found that the extent of fiber-matrix reactions in Ti/SiC composites fabricated by the RIF technique is noticeably affected by both an increase in Ti content and by the processing temperature. Uncoated SiC fibers extensively react with the titanium alloy matrix at 1200 C, whereas no reaction occurs when coated SiC fibers are used.
    Keywords: COMPOSITE MATERIALS
    Type: Scripta Metallurgica et Materialia (ISSN 0956-716X); 28; 3; p. 313-318.
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