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Maahs, Howard G.

Publications and source records attributed to Maahs, Howard G..

7 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Four advances in carbon-carbon materials technology

Carbon-carbon composites are a specialty class of materials having many unique properties making these composites attractive for a variety of demanding engineering applications. Chief among these properties are exceptional retention of mechanical properties at temperatures as high as 4000 F, excellent creep resistance, and low density (1.6 to 1.8 g/cu cm). Although carbon-carbon composites are currently in service in a variety of applications, much development work remains to be accomplished before these materials can be considered to be fully mature, realizing their full potential. Four recent technology advances holding particular promise for overcoming current barriers to the wide-spread commercialization of carbon-carbon composites are described. These advances are: markedly improved interlaminar strengths (more than doubled) of two dimensional composites achieved by whiskerization of the fabric reinforcing plies, simultaneously improved oxidation resistance and mechanical properties achieved by the incorporation of matrix-phase oxidation inhibitors based on carborane chemistry, improved oxidation resistance achieved by compositionally graded oxidation protective coatings, and markedly reduced processing times (hours as opposed to weeks or months) accomplished through a novel process of carbon infiltration and coatings deposition based on the use of liquid-phase precursor materials.

Maahs, Howard G.↗
NASA NTRS1992

Recent advances in carbon-carbon substrate technology at NASA. Langley Research Center

A comparison of specific strengths of candidate high-temperature materials as a function of temperature is shown. From this comparison, it is apparent why there is an interest in carbon-carbon composites for applications as a strong, light-weight thermal protection system (TPS), or as hot structure, for applications above 2500 F. The lower bound of the carbon-carbon band is representative of the tensile strength of cross-ply Advanced Carbon-Carbon (ACC). The upper bound represents capabilities of various experimental carbon-carbon composites. Thin carbon-carbon composites, such as would be used as TPS panels or hot aero-structure, are usually constructed of layups of 2-D fabrics of carbon-fiber yarns (tows). Although the in-plane strengths of these composites can be very attractive, a major problem area is low interlaminar strength. The low interlaminar strength is the result of a relatively weak carbon matrix and poor interaction between the fibers and matrix. The purpose of this paper is to discuss strategies being employed to improve the interlaminar strengths of the materials at the upper bound of the carbon-carbon band, and to present some recent encouraging results. The emphasis of these strategies is to improve interlaminar shear and tensile strengths while maintaining, or even improving, the inplane properties.

Ransone, Philip O.↗
NASA NTRS1992

Carbon-carbon composites

The current applications of C-C composites extend to aircraft brakes, rocket nozzles, missile nosetips, and leading edges of the Space Shuttle. More advanced, secondary and even primary structure applications in cyclic, high-temperature oxidizing environments depend on effective oxidation protection for repeated missions. Accounts are presently given of state-of-the-art methods in substrate fabrication, carbon deposition, and SiC and Si3N4 protective coatings. Attention is given to current levels of high temperature oxidation protection for various mission and vehicle types, as well as to performance projections for C-C composites used by a representative National Aerospace Plane airframe structure. Future technology requirements in C-C composites are projected.

Maahs, Howard G.↗
NASA NTRS1990

Active-to-passive transition in the oxidation of silicon carbide and silicon nitride in air

The active-to-passive transition in the oxidation of SiC and Si3N4 was determined in a flowing air environment as a function of temperature and total pressure. The experimentally observed transition temperatures ranged from a low of 1347 C to a high of 1543 C for partial pressures of oxygen of 2.5 and 123.2 Pa, respectively. The SiC and Si3N4 samples had approximately the same transition point for a given pressure. In general, the higher the flow rate, the higher the transition temperature for a given pressure. The transitions for SiC measured in this study agree with previous data for the transition of SiC measured in pure oxygen at reduced pressures and in oxygen inert gas mixtures.

Vaughn, Wallace L.↗
NASA NTRS1989

Carbon-carbon composites: Emerging materials for hypersonic flight

An emerging class of high temperature materials called carbon-carbon composites are being developed to help make advanced aerospace flight become a reality. Because of the high temperature strength and low density of carbon-carbon composites, aerospace engineers would like to use these materials in even more advanced applications. One application of considerable interest is as the structure of the aerospace vehicle itself rather than simply as a protective heat shield as on Space Shuttle. But suitable forms of these materials have yet to be developed. If this development can be successfully accomplished, advanced aerospace vehicles such as the National Aero-Space Plane (NASP) and other hypersonic vehicles will be closer to becoming a reality. A brief definition is given of C-C composites. Fabrication problems and oxidation protection concepts are examined. Applications of C-C composites in the Space Shuttle and in advanced hypersonic vehicles as well as other applications are briefly discussed.

Maahs, Howard G.↗
NASA NTRS1988

Response of carbon-carbon composites to challenging environments

This paper presents results from material performance evaluations of oxidation-resistant carbon-carbon composites intended for multiuse aerospace applications, which cover the effects of the following environmental parameters: the oxidizing nature of the environments (including both high and low oxygen partial pressures), high temperatures, moisture, cyclic temperature service, and foreign-object impact. Results are presented for the carbon-carbon material currently in use as the thermal-protection-system material on Space Shuttle, as well as for newer and more advanced structural forms of carbon-carbon composites.

Maahs, Howard G.↗