Showing papers on "Ceramic matrix composite published in 1993"

Carbon-carbon composites

Abstract: Part 1 Introduction: carbon bonding in carbon materials order and disorder in carbon materials techniques for characterizing the structure of carbons definition of carbon forms and processes carbon composites carbon-carbon composites. Patr 2 Carbon fibres: processing of carbon fibres the structure of carbon fibres commercially available fibres surface treatment of carbon fibres and interfacial bonding carbon fibre product form. Part 3 Gas phase impregnation/densification of carbon-carbon and other high-temperature composite materials: the CVD process physics - chemical principles of the CVD process experimental CVD techniques CVD processing of carbon-carbon composites CVD processing of ceramic matrix composites a brief study of commercial CVD composite fabrication processes. Part 4 Thermosetting resin matrix precursors: general considerations isotropic carbon carbon yield from polymers carbonization of composites graphitization impregnation technology high carbon yield matrix precursors. Part 5 Thermoplastic matrix precursors: pitch characterization of pitches pyrolysis of pitches carbon yield from pitch the influence of additives on carbonization control of microstructure in pitch-derived carbon-carbon composites low-pressure composites processing high-pressure processing of pitch derived carbon-carbon thermoplastic polymer matrix precursors. Part 6 Oxidation behaviour of carbon-carbon: fundamental concerns in the oxidation protection of carbon-carbon composites protection at temperatures below 1500 degrees C protection coating for the 1500-1800 degree C range oxidation protection at temperatures in excess of 1800 degrees C. Part 7 Raw materials: densification of composites by CVD fabrication of thermoset resin laminated precursors processing thermoplastic precursors graphitization of carbon-carbon mechanical testing of carbon-carbon microscopy density and porosity measurements oxidation and oxidation protection measurement of thermal conductivity. Part 8 The properties of carbon-carbon composites: general consierations microstructure interfaces in carbon-carbon composites mechanical properties thermal properties electromagnetic properties. Part 9 Applications of carbon-carbon composites: brakes and clutches rocket motors heatshields for re-entry vehicles aero-engine components industrial applications biomedical devices. Part 10 Technology summary and market review: the state of the art the carbon-carbon market commercializing a product organization of the carbon-carbon business major companies in the carbon-carbon market.

High Temperature Ceramic Matrix Composites

Abstract: High temperature ceramic matrix composites , High temperature ceramic matrix composites , مرکز فناوری اطلاعات و اطلاع رسانی کشاورزی

Ceramic Matrix Composites

Abstract: The present state of the knowledge of ceramic-matrix composites have been reviewed. The fracture toughness of present structural ceramics are not enough to permit design of high performance machines with ceramic parts. They also fail by catastrophic brittle fracture. It is generally believed that further improvement of fracture toughness is only possible by making composites of ceramics with ceramic fibre, particulate or platelets. Only ceramic-matrix composites capable of working above 1000 degree centigrade has been dealt with keeping reinforced plastics and metal-reinforced ceramics outside the purview. The author has discussed the basic mechanisms of toughening and fabrication of composites and the difficulties involved. Properties of available fibres and whiskers have been given. The best results obtained so far have been indicated. The limitations of improvement in properties of ceramic-matrix composites have been discussed.

Fibre-matrix interphases and interfaces in ceramic matrix composites processed by CVI

Abstract: The fibre-matrix (FM) interfacial zone plays a key role in the mechanical behaviour of Si-C(O)/SiC inverse composites fabricated by chemical vapour infiltration (CVI) from ex-polycarbosilane Si-C(O) fibres precoated with pyrocarbon or boron nitride. It consists not only of the C (or BN) main interphase, but also of very thin secondary interphases (i.e. carbon and silica) resulting from the decomposition of the metastable Si-C(O) fibres thought to occur during the fabrication of the fibres and/or the composites. The FM interfacial zone may play two complementary roles: (i) it provides low-energy microcrack propagation paths parallel to the fibre axis, and (ii) it may act as a compliant buffer for the relaxation of the residual thermal compression stresses on the interface. The FM bond strength is low or moderate when a quasi-continuous thin layer of anisotropic carbon is present between the fibre and the main interphase and when the fibre surface remains smooth. The mechanical behaviour in tension is non-b...

Matrix cracking in unidirectional ceramic matrix composites under quasi-static and cyclic loading

Abstract: Experimental data associated with the development of matrix cracks in unidirectional continuous silicon carbide fibre/calcium alumino-silicate matrix laminates under quasi-static loading are presented, including crack density, residual strain and hysteresis behaviour as functions of applied stress. Simple models are developed, based on an assumption of purely frictional load transfer between the fibre and matrix, which describe reasonably well the quasi-static stress-strain behaviour in the presence of cracks. Under tension-tension mechanical fatigue cycling it is found that the crack density stabilises at a relatively early stage in the test. Based on the quasi-static model, the changes in fatigue hysteresis loops on fatigue cycling are interpreted in terms of a reduction in the effective frictional interfacial shear stress.

Advances in composite tribology

Abstract: Part 1 The tribology of composite materials: a preface. Part 2 Tribology of polymer composites: friction and wear of self-reinforced thermoplastics, J. Song and G.W. Ehrenstein reciprocating dry friction and wear of short-fibre reinforced polymer composites, A. Schelling and H.H. Kausch short-fibre reinforced, high-temperature resistant polymers for a wide field of tribological applications, A.M. Haeger and M. Davies developments in tribology of fibre reinforced composites with thermoplastic and thermosetting matrices, U.S. Tewari and J. Bijwe wear models for multiphase materials and synergistic effects in polymeric hybrid composites, K. Friedrich. Part 3 Tribology of ceramic, glass and metal matrix composites: tribology of ceramic matrix composites against metals, K. Fukada and M. Ueki wear mapping for metal and ceramic matrix composites, P.K. Rohatgi et al performance of metal matrix composites under various tribological conditions, S. Wilson and A. Ball tribological properties of unidirectionally oriented carbon fibre reinforced glass matrix composites, Z. Lu friction and wear characteristics of advanced ceramic composite materials, B. Prakash erosion of metal matrix composites, I.G. Greenfield. Part 4 Tribology of composite materials for special applications: tribology of composites for magnetic tape recording, H. Jacobi and U. Nowak friction and wear of polymers, ceramics and composites in biomedical applications, G.W. Stachowiak high-speed tribology of polymer composites, I. Narisawa tribology of composites used as frictional materials, G. Crosa and I.J.R. Baumvol. Part 5 Tribological response of composites in relation to other requirements: rolling contact fatigue of polymers and polymer composites, T.A. Stolarski fretting and fretting fatigue of advanced composite laminates, K. Schulte et al tribological facets of polymer composites fabrication, D.R. Williams.

Ceramic composite coating material

Abstract: A ceramic coating for a metal article includes a metallic bond coat deposited on the metal article, at least one MCrAlY/ceramic layer deposited on the bond coat, and a ceramic composite top layer deposited on the MCrAlY/ceramic layer. The M in MCrAlY stands for Fe, Ni, Co, or a mixture of Ni and Co. The ceramic in the MCrAlY/ceramic layer comprises mullite, alumina, zircon, silimanite, sodium zirconium phosphate, fused silica, cordierite, aluminum titanate, or zirconia. The ceramic composite top layer comprises a ceramic matrix and at least one secondary phase. A method of making the coating includes sequentially depositing a metallic bond coat on the metal article, at least one MCrAlY/ceramic layer on the bond coat, and a ceramic composite top layer on the MCrAlY/ceramic layer.

The ultimate tensile strength of metal and ceramic-matrix composites

Abstract: The tensile strength of ceramic and metal matrix composites is subject to an important role of the fiber/matrix interface. The mechanical properties of this interface dictate the stress concentration that develops in fibers that surround a failed fiber. An analysis of this phenomenon is used to illustrate interface conditions that sufficiently diminish the stress concentration that a global load sharing criterion may be used to prescribe the contribution of the fibers to the composite strength. This, in turn, leads to a criterion for the transition to failure by local load sharing.

Characterization of Interlaminar Shear Strength of Ceramic Matrix Composites

Abstract: The interlaminar shear strengths of three ceramic matrix composites have been characterized using a double-notch shear (DNS) test. The material systems investigated are plain woven C/SiC, plain woven SiC/SiC, and cross-plied SiC/calcium aluminosilicate-II. The use of the double-notch shear test for measuring the interlaminar shear strength of ceramic matrix composites is evaluated first. Numerical stress analyses are performed to investigate the effect of DNS specimen length, notch distance, and specimen supporting jig on the stress distribution in the expected fracture plane and the interlaminar shear strength. The numerical findings are then compared with an analytical model proposed elsewhere and correlated with the experimental results. The validity of this test technique has been established.

Delamination, fibre bridging and toughness of ceramic matrix composites

Abstract: Delamination cracks in long-fibre reinforced ceramic matrix composites are found to be bridged by fibres which span the crack wake at a shallow angle. The in situ observation of bridging fibres reveals that these are subject to considerable tensile forces, giving rise to a substantial crack closure force. The overall crack closure force is determined by the number of bridging fibres, steadily reduced by fibre failure caused by high bending moments at the root of each fibre. This leads to a model for crack closing forces combining simple mechanics and Weibull statistics. The model relates these forces to the properties of fibres, matrix and their interface.

Method of fabrication of composites

Abstract: A method of making a fiber-reinforced ceramic matrix composite of complex shape by first rigidifying a fibrous arrangement made of woven or braided material by impregnating with a preceramic resin, and then curing and pyrolyzing the resin to form a rigid or stiff preform. The rigid preform is then densified by chemical vapor infiltration, e.g., using a forced-flow/thermal-gradient process. Using three-dimensional woven fabrics made of ceramic fibers, such as silicon carbide or silicon nitride, strong high-temperature resistant composites are produced having porosities from about 20 percent to less than about 5 percent.

Method for making a ceramic metal composite.

Abstract: The present invention is directed to a process for fabricating ceramic-metal composites having continuous ceramic and metal phases. The process includes the steps of contacting a porous ceramic matrix material with a molten metal whereby capillary action pulls the metal into the ceramic matrix to substantially fill the void space. The present invention also provides a ceramic-metal composite having continuous metal and ceramic phases.

Monolithic fuel cell having improved interconnect layer

Abstract: A fuel cell comprises an anode, a cathode, a solid electrolyte disposed between the anode and the cathode, and interconnect means for providing an electrical connection located adjacent to either the cathode or the anode but not adjacent to the solid electrolyte. The interconnect means includes an interconnect layer having a composition of (i) a mixture of an electrical conductor and a ceramic matrix material that is sinterable in an oxidizing atmosphere at a temperature of less than about 1500° C., (ii) a mixture of a lanthanum chromite-based ceramic and a yttrium chromite-based ceramic, or (iii) a yttrium chromite-based ceramic of the form Yw-x-y Cax Zry Crv-z Znz O3 , where w is from about 0.9 to about 1.1, x is from about 0.1 to about 0.3, y is from about 0.001 to about 0.1, z is from about 0.1 to about 0.3, and v is from about 1 to about 1.2.

Fiber pull-out and strain localization in ceramic matrix composites

Abstract: THE MECHANICAL properties of ceramic matrices uniaxially reinforced with strong continuous fibers depend on a wide variety of material parameters: the fiber and matrix elastic moduli, the matrix toughness, the statistical fiber strength, the fiber radius and fill fraction, and the sliding resistance tau between the fibers and the matrix. A major contribution to the work of fracture is the work to pull-out broken fibers from the matrix against the sliding resistance. Recent analytic theories of the pull-out predict finite pull-out for very narrow fiber strength distributions, in contrast to prior theories and ideas suggesting zero pull-out. The theories also assume that fiber cracking is distributed throughout the composite and not localized to some narrow region; such strain localization could modify composite properties tremendously. Here, both analytical arguments and numerical simulations are used to show that finite pull-out does exist for narrow fiber strength distributions. The numerical simulations also demonstrate that strain localization does occur, but that it (i) does not affect the ultimate tensile strength, and (ii) reduces pull-out only slightly but with the detailed trends in pull-out properties predicted by the analytic theory retained. Some basic tenets and results of the analytic models are thus robust and so the analytic models should serve as powerful tools for composite optimization.

Combined Mode I and Mode II Fracture of Monolithic Ceramics

Abstract: The mode I, mode II, and combined mode I-mode II fracture behaviors of a coarse-grained silicon nitride, a fine-grained silicon nitride, and an alumina were investigated. These ceramics were fractured from two types of fracture initiating flaws: small surface flaws and large single edge precracks. The small surface flaws were introduced by Knoop indentation in flexural samples at various angles to the tensile stress direction and fractured in four-point bending. The samples with large precracks were fractured in the asymmetric four-point-bend geometry. The mixed-mode fracture toughness values obtained from the two flaw configurations were in good agreement with each other. All three ceramics displayed very similar mixed-mode fracture behavior, although their microstructures were not similar. Comparison of experimental data to mixed-mode fracture theories revealed that the minimum strain energy density theory best described the mixed-mode fracture behavior of all three ceramics.

Fiber and Whisker Reinforced Ceramics for Structural Applications

Abstract: "Introduction Properties of Structural Materials Toughening Mechanisms in Ceramic Matrix Composites Mechanical Testing of Ceramic Matrix Composites Fibers and Whiskers for Ceramic Reinforcement Fiber Architecture Selection of Compatible Reinforcement and Matrix Materials Importance of the Fiber/Matrix Interface in Ceramic Matrix Composites Fiber Coatings Slurry Processing of Whisker Reinforced Ceramics Slurry Processed Continuous Fiber Reinforced Ceramics Ceramic Matrix Composites Produced by Reaction Bonding Matrix Formation by Macromolecule Decomposition Production of Ceramic Matrix Composites by Chemical Vapor Infiltration Melt Processing of Ceramic Matrix Composites Machining, Joining, Nondestructive Evaluation, and Design Applications of Ceramic Matrix Composites "

Process for producing a porous ceramic and porous ceramic composite structure utilizing combustion synthesis

Abstract: A process for producing a porous ceramic, ceramic composite or metal-ceramic composite structure by combustion synthesis wherein a foamed polymer shape is impregnated with a slurry of ceramic precursors and ignited to initiate combustion synthesis, thereby obtaining a ceramic, ceramic composite or metal-ceramic composite article having interconnected porosity. Ceramic composite filters having improved strength, toughness and thermal shock resistance are provided, with the ceramic composite being an oxide and a nonoxide.

Ultrasonic reflectivity technique for the characterization of fiber‐matrix interface in metal matrix composites

Abstract: An ultrasonic plane wave reflected by a cylindrical fiber embedded in a homogeneous isotropic matrix is modeled. The model calculates the ‘‘back‐reflection’’ coefficient by taking in to account the properties of the fiber and the matrix, the ultrasonic wavelength, the angle of incidence, and a coefficient called ‘‘shear stiffness coefficient’’ which characterizes the elastic behavior between the fiber and the matrix. Results obtained from the theoretical analysis for a model metal matrix composite system are shown. The theory developed in this paper and some of the results obtained are equally applicable in ceramic matrix fiber reinforced composites.

Analysis of Damage in a Ceramic Matrix Composite

Abstract: Mechanisms of damage and the associated mechanical response are stud ied for a unidirectionally fiber-reinforced ceramic matrix composite subjected to uniaxial tensile loading parallel to fibers. A multi-stage development of damage is identified, and for each stage the governing mechanisms are discussed. For distributed matrix micro cracking a continuum damage model is used as the basis for describing the associated stress-strain behavior. A simplified analysis of frictional sliding at the fiber/matrix inter face is made to elucidate its effect on the stress-strain response.

Thermal response and ablation characteristics of light weight ceramic ablators

Abstract: An account is given of the thermal performance and ablation characteristics of the NASA-Ames Lightweight Ceramic Ablators (LCAs) in supersonic, high-enthalpy convective environments, which use low density ceramic or carbon fiber matrices as substrates for main structural support, with organic resin fillers. LCA densities are in the 0.224-1.282 g/cu cm range. In-depth temperature data have been obtained to determine thermal penetration depths and conductivity. The addition of SiC and PPMA is noted to significantly improve the ablation performance of LCAs with silica substrates. Carbon-based LCAs are the most mass-efficient at high flux levels.

Coating a composite article by applying a porous particulate layer and densifying the layer by subsequently applying a ceramic layer

Abstract: Carbon or ceramic matrix composites are protected from oxidation at high temperatures by a layer formed from a mixture of solid particles in a binder which is cured and then coated with ceramic material by chemical vapor infiltration.

Sliding Wear of Silicon Carbide—Titanium Boride Ceramic‐Matrix Composite

Abstract: The tribological behavior of a SiC–TiB2 ceramic-matrix composite was evaluated using a pin-on-flat contact configuration in reciprocating sliding. A steady-state friction coefficient of about 0.55 and an average specific wear rate of about 2 × 10-6 mm3·N-1·m-1 were measured. The mechanisms of material removal involved failure of the particle–matrix interface, resulting in particle pullout and chipping of the matrix material. The generated wear debris was often recycled through the contact interface, resulting in the production of submicrometer fine particles that reattached to the surface and were later removed in flake form. Transitions were observed in the specific wear rate from higher to lower values as sliding progressed. These transitions were accompanied by transitions in the nominal contact pressure.