Showing papers on "Ceramic matrix composite published in 1985"

Failure Mechanisms in Ceramic‐Fiber/Ceramic‐Matrix Composites

Abstract: Mechanisms of failure in a unidirectional Sic-fibe/glass-ceramic composite are investigated using in situ observations during tensile and flexural loading. These experiments show that failure in tension occurs in several stages (similar to certain other brittle fiber composites): multiple matrix cracking, followed by fiber fracture and pullout. In flexural loading the failure process is more complex. Consequently, the flexural test cannot be used for measurement of tensile strength (although it can be used for measurement of the stress for matrix cracking). The application of conventional fracture mechanics to describe tensile failure is discussed. The in situ observations provide direct indication of the importance of frictional bonding between the matrix and fibers. Some novel methods for measuring the frictional forces and residual stresses are investigated, and the influence of surface damage on strength is assessed.

Development of SiC-whisker-reinforced ceramics

Abstract: Dense, toughened SiC-whisker-reinforced ceramic matrix (ie Al2O3 and mullite) composites were fabricated by hot-pressing powder-whisker mixtures The densification behavior of the composites was influenced by the temperature, pressing pressure, and whisker content but even at 60 vol pct whisker loading, full density was achieved at 1850 C for the alumina matrix The mechanical performance of these composites was improved In particular, the critical stress intensity factor (equal to about 9 MPa sq rt of m in Al2O3 and equal to about 5 MPa sq rt of m in mullite) exhibited substantial improvements (approximately two-fold increases) over monolithic ceramics In the case of the alumina-20 vol pct SiC whisker composite, the flexural strength was 805 MPa at room temperature and 520 MPa at 1200 C the thermal conductivity was 32 W/mK at room temperature and 10 W/mK at 1000 C 19 references

BN coating of ceramic fibers for ceramic fiber composites

Abstract: A ceramic fiber composite material comprised of boron nitride coated cera fibers embedded in a ceramic matrix. The boron nitride coating limits both physical bonding and chemical reaction between the fibers and matrix to improve both strength and toughness of the composite material.

Tensile mechanical properties of SiC whiskers

Abstract: An initial evaluation has been made of the tensile mechanical properties of SiC whiskers synthesized by a vapour-liquid-solid process. A micro-tensile tester and associated testing techniques were developed for this purpose. The SiC whiskers exhibit an average tensile strength of 8.40 GPa (1 220 000 psi) and an average elastic modulus of 581 GPa (84 300 000 psi), and were considerably stronger and stiffer than continuous, polycrystalline SiC fibres. These results indicate the significant potential of SiC whiskers as short-fibre reinforcement elements for ceramic matrix composites.

Ceramic Matrix for Large Scale Animal Cell Culture

Abstract: A ceramic matrix having a high degree of surface area per unit volume is shown to have significant utility in the large scale culture of animal cells. The surfaces of the ceramic provide for the adhesion and growth of a wide variety of cells to densities equal to or greater than obtained with other methods such as roller bottles or microcarriers. Utilizing an automated system controlling pH and dissolved oxygen, scale-up from 0.9 m2 to 18.5 m2 of surface area was accomplished with no losses in efficiency of surface utilization. The density of Vero cells after 7–8 days culture under standard conditions averaged 6.6 × 105 cells/cm2 for each size of ceramic. Methods providing continuous monitoring of the culture through analysis of the cellular oxygen consumption rate and complete cell harvesting are described.

Method for densification of ceramic materials

Abstract: Supercritical fluids may be used to carry ceramic precursor materials into the pores of a ceramic host. Reducing the solubility of the ceramic precursor in the supercritical fluid will cause deposition of the ceramic precursor in the pores or void spaces of the ceramic host and accomplish densification of the ceramic host material.

Inorganic fiber-reinforced ceramic composite material

Abstract: An inorganic fiber-reinforced ceramic composite material comprising a matrix of a ceramic and inorganic fibers as a reinforcing material, characterized in that (a) the inorganic fibers are specified inorganic fibers containing silicon, either titanium or zirconium, carbon and oxygen, (b) the ceramic is at least one material selected from the group consisting of carbides, nitrides, oxides, glass ceramics, graphite and specified inorganic materials containing silicon, either titanium or zirconium, carbon and oxygen, (c) the inorganic fibers have an initial reaction degradation speed of not more than 0.35 kg/mm2.sec-1 and a tenacity reduction ratio of not more than 40% during the production of the composite material, (d) the composite material has a critical stress intensity factor about 2 to 7 times as high as that of said matrix alone, and (e) the composite material has a bending strength reduction ratio, measured by a thermal shock fracture resistance measuring method, of not more than about 10% after it is heat-treated in air at 800° to 1300° C., immediately then dipped in water at room temperature, and then dried.

Room‐Temperature Mechanical Behavior of Fiber‐Reinforced Ceramic‐Matrix Composites

Abstract: Ceramic-matrix composites reinforced with SiC fibers were tested at room temperature both in, flexural and tensile configurations. The stress-strain behavior for composites tested in tension was correlated with progressive microcracking and failure processes. Significant differences between failure modes in tension and flexure were observed.

Process for the manufacture of a composite material with refractory fibrous reinforcement and ceramic matrix

Abstract: A thin, refractory, intermediate adhesive layer of laminar structure is deposited in oriented fashion on the reinforcing fibers by chemical vapor deposition, this intermediate layer having a greater elongation at break than the matrix and having a thickness of between 0.2 and 3 micrometers; the material forming the intermediate layer can be laminar pyrocarbon or boron nitride; the ceramic matrix is then infiltered, preferably by chemical vapor deposition, inside the pores of the reinforcement.

Fibers for Structurally Reliable Metal and Ceramic Composites

Abstract: In their current state of development, commercially available reinforcing fibers fail to meet the requirements formulated for metal or ceramic matrix composites of sufficient strength and toughness. Attention is presently given to criteria for high strength and toughness in metal and ceramic matrix composites, as well as the approach adopted in fiber evaluation as a result of studies at the NASA Lewis Research Center. Two areas of special interest have been strength improvement in large diameter boron fibers for tough, impact-resistant boron/aluminum composites, and the evaluation of SiC fibers as reinforcement in tough ceramic-matrix composites with service temperatures of the order of 1400 C.

Ceramic composite material having a core of ceramic fibers coated with a layer of ceramic, and method of producing same

Abstract: Ceramic composite material characterized in that it comprises a core of ceramic fibers of which at least one face is coated with a hard and dense ceramic slip covering, of which the coefficient of expansion is compatible with that of the ceramic fibers.

Process for producing shaped ceramic articles reinforced by short fibres

Abstract: 1. Process for the production of a short fibrereinforced, ceramic bocy, characterized in that one casts a fine homogeneous slurry formed from the ceramic matrix powder and whiskers with an acceleration of g>=1 into a mould, subsequently dries and thereather sinters and hot-isostatically post-consolidates or directly hot-isostatically consolidates without sintering.

Method for producing ceramic articles of increased fracture toughness

Abstract: Ceramic articles having improved fracture toughness are prepared by ion bombardment of ceramic particles by gas ions to impregnate the particles, cold compacting the gas ion-containing ceramic particles into a form, and hot pressing the gas ion-containing ceramic particle form into a ceramic article whereby gas bubbles are formed in and substantially homogeneously dispersed throughout the ceramic article.

Ceramics containing dispersants for improved fracture toughness

Abstract: The invention is a ceramic composition containing a new class of dispersant for hindering crack propagation by means of one or more energy-dissipative mechanisms. The composition is composed of a ceramic matrix with dispersed particles of a transformation-prone rare-earth niobate, tantalate or mixtures of these with each other and/or with a rare-earth vanadate. The dispersants, having a generic composition tRMO 4 , where R is a rare-earth element, B is Nb or Ta and O is oxygen, are mixed in powder form with a powder of the matrix ceramic and sintered to produce a ceramic form or body. The crack-hindering mechanisms operates to provide improved performance over a wide range of temperature and operating conditions.

Process for producing ceramic of high heat resistance and especially a ceramic component fabricated by this process

Abstract: In a process for producing ceramic of high heat resistance, at least one fibre ply of the same type of ceramic is attached to or incorporated in a green ceramic matrix to be sintered before the actual sintering step, in order to produce reinforced ceramic components of high heat resistance and high stress tolerance. The fiber ply is not fully infiltrated by the ceramic matrix. Due to the partially homogeneous bonding between the bonding materials of the same type, the reinforcing fiber ply has, with a ceramic component fabricated in accordance with the invention in operation, the effect of stopping cracks and securing fragments.

Comparison of the Various New High Modulus Fibers for Reinforcement of Advanced Composites with Polymers, Metals and Ceramics as Matrix

Abstract: High modulus fibers are used mainly as fibrous reinforcement in resins, metals, or ceramics to provide strength and stiffness. It is instructive to consider what factors led to the development of composites. Structural designs are as likely to be limited by the stiffness as by the strength of the construction material. Hence, engineers have always desired suffer, stronger, less dense and lower cost structural materials. There are a number of materials in the upper center part of the periodic table, such as boron, carbon, silicon carbide and alumina, which all have significantly higher modulus/weight ratios than the common engineering metals. Theoretically, the high modulus would result in high strength if the materials were perfect. Unfortunately, most of the high modulus materials are covalently bonded and are brittle. Small flaws can produce catastrophic failure at drastically reduced stresses. (The flaws may be introduced during manufacture or during service.) Except in some unusual protected environments, primary structural elements can not be made from materials which fail catastrophically. Composite materials offer the potential of using these brittle materials in structures which will not fail catastrophically. The brittle materials are made into fibers to give redundancy and placed into a matrix. The matrix serves to transfer stress into and out of the fibers. The matrix and matrix/fiber interface must also serve to stop cracks which originate in the fibers from propagating through the solid. Hence, a localized impact may break a few fibers, but the crack can be stopped by a ductile matrix or fiber/matrix debond.

Test method development for structural characterization of fiber composites at high temperatures

Abstract: Test methods used for structural characterization of polymer matrix composites can be applied to glass and ceramic matrix composites only at low temperatures. New test methods are required for tensile, compressive, and shear properties of fiber composites at high temperatures. A tensile test which should be useful to at least 1000 C has been developed and used to characterize the properties of a Nicalon/glass composite up to the matrix limiting temperature of 600 C. Longitudinal and transverse unidirectional composite data are presented and discussed.

Polymer, metal and ceramic matrix composites for advanced aircraft engine applications

Abstract: Advanced aircraft engine research within NASA Lewis is being focused on propulsion systems for subsonic, supersonic, and hypersonic aircraft. Each of these flight regimes requires different types of engines, but all require advanced materials to meet their goals of performance, thrust-to-weight ratio, and fuel efficiency. The high strength/weight and stiffness/weight properties of resin, metal, and ceramic matrix composites will play an increasingly key role in meeting these performance requirements. At NASA Lewis, research is ongoing to apply graphite/polyimide composites to engine components and to develop polymer matrices with higher operating temperature capabilities. Metal matrix composites, using magnesium, aluminum, titanium, and superalloy matrices, are being developed for application to static and rotating engine components, as well as for space applications, over a broad temperature range. Ceramic matrix composites are also being examined to increase the toughness and reliability of ceramics for application to high-temperature engine structures and components.

Improvements in the fabrication of ceramic-fiber-ceramic-matrix composites by chemical vapor infiltration

Abstract: Development of a new, faster process for the fabrication of ceramic-fiber-reinforced-ceramic-matrix composites by chemical vapor infiltration has continued. Composites of SiC fibers infiltrated with a matrix of either SiC or Si/sub 3/N/sub 4/ have been produced. Process and equipment improvements led to the fabrication of preforms with a higher fiber content, and infiltration improvements reduced infiltration times and increased infiltrated densities. These improvements have produced composites with higher flexural strengths (up to 475 MPa) and high strain values (up to 1%). The high strength and high strain values along with the gradual loss of strength (in contrast to the sudden loss typical of ceramics) were major goals of this work.

NASA space materials research

Abstract: The effect of the space environment on: (1) thermal control coatings and thin polymer films; (2) radiation stability of 250 F and 350 F cured graphite/epoxy composites; and (3) the thermal mechanical stability of graphite/epoxy, graphite/glass composites are considered. Degradation in mechanical properties due to combined radiation and thermal cycling is highlighted. Damage mechanisms are presented and chemistry modifications to improve stability are suggested. The dimensional instabilities in graphite/epoxy composites associated with microcracking during thermal cycling is examined as well as the thermal strain hysteresis found in metal-matrix composites.

Crack resistance of a constructional ceramic

Abstract: The purpose of this article is the development and substantiation of methods of determination of crack resistance and the investigation of features of fracture of a machine building ceramic intended for use at high temperatures. Studied were a silicon nitride base reaction-sintered ceramic, designated NKKKM, and self-bonded silicon carbide produced by industry. Electrical porcelain and sodium glass were used as model materials in the development and testing of the methods.

Manufacture of part made of high-temperature resisting ceramic

Abstract: Ceramic components are made by forming, prior to sintering, a green ceramic matrix with at least one fibre layer consisting of similar ceramic material in or on the matrix with no, or only partial, infiltration of the matrix material into the fibre layer, and then sintering the matrix and fibre layer together The matrix and fibre layer may be formed together by putting the latter in a mould and slip casting the matrix, or by isostatic pressing the matrix and fibre layer(s) together in a mould Owing to the partially homogeneous union between similar composite materials the reinforcing fibre layer produces a crack-stopping and fragment-containing effect in the event of rupture of the ceramic component

High temperature metal and ceramic composites

Abstract: The Materials Division at NASA Lewis is engaged in research and development efforts on behalf of fiber-reinforced composite materials that are lighter, stiffer, and more structurally reliable than conventional monolithic alloys and ceramics in applications that range from the cryogenic to the refractory. Attention is presently given to metal matrix composites, in which high performance depends on stiff, strong and thermally stable large diameter fibers, with chemically stable interfacial bonding and good coefficient of thermal expansion matching between fibers and matrices, and to ceramic matrix composites, in which intermediate strength interfacial bonds must allow cracks to propagate through the matrix only, while retaining good load transfer characteristics between fiber and matrix.