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At least 127 records · Page 7

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NASA NTRS1972

Determining and analyzing the strength and impact resistance of high modulus glass

A number of new glass compositions have been prepared with increased emphasis on compositions without beryllia. Glass preparations have been much more broadly based and have included the eutectic glass fields, and the mullite-rare earth glass systems. Of the new glasses, the best non-toxic composition is UARL 472 with a bulk modulus of only 18.20 million psi. A second experimental glass, UARL 417, was chosen for research in making large quantities of fiber in monofilament form. Tests of these UARL 417 epoxy resin samples in comparison to similar composites made with the DuPont organic fiber, PRD-49-1, show that the UARL composites have a compressive strength 41/2 times higher and a specific compressive strength at least 21/2 times greater. Much of the research effort attempted to answer the question of why a given glass should have an impact strength superior to other glasses. No definitive answer to the question was found.

Bacon, J. F.↗

NASA NTRS1972

Some important aspects in testing high-modulus fiber composite tubes designed for multiaxial loading

Tubular specimens were potted in metal grips to determine the feasibility of this gripping method in applying multiaxial loads. Strain gage rosettes were used to assess grip transitional strains, through thickness strain variation and strain variations along the tube length and circumference. The investigation was limited to loading 0 deg, + or - 45 deg, and 90 deg graphite/epoxy and glass/epoxy tubes in axial tension. Results include modifications made to the grips to reduce transitional strains, illustrations of the tube failure modes, and some material properties. The gripping concept shows promise as a satisfactory technique for applying multiaxial loads to high strength, high modulus fiber composite tubes.

Sullivan, T. L.↗

NASA NTRS1972

Some important aspects in testing high-modulus fiber composite tubes designed for multiaxial loading.

Tubular specimens were potted in metal grips to determine the feasibility of this gripping method in applying multiaxial loads. Strain gage rosettes were used to assess grip transitional strains, through thickness strain variation and strain variations along the tube length and circumference. The investigation was limited to loading 0, 45, plus or minus 45, and 90 deg graphite/epoxy and glass/epoxy tubes in axial tension. Results include modifications made to the grips to reduce transitional strains, illustrations of the tube failure modes, and some material properties. The gripping concept shows promise as a satisfactory technique for applying multiaxial loads to high-strength, high-modulus fiber composite tubes.

Sullivan, T. L.↗

NASA NTRS1973

High modulus filament wound vessels for cryogenic containers in spacecraft.

Compared to metallic vessels, filament-wound vessels for containment of cryogens and high pressure gases offer high potential weight savings for NASA spacecraft applications. Since carbon fiber/epoxy resin composites exhibit high strength-to-density ratios, high-cycle fatigue life, and excellent strain compatibility with internal metallic liners, filament-wound carbon fiber/epoxy resin composites were evaluated for application to cryogenic internal pressure vessels. Compared to room temperature values, the cryogenic strengths of the composites were reduced by about 15% at -423 F (with the exception of one composite) while moduli increased as much as 25%. Filament-wound carbon fiber/epoxy resin vessel specimens, made by three fabricators, defined and solved problems in the processing of these friable high-modulus fibers into structurally efficient vessel specimens.

Simon, R. A.↗

NASA NTRS1973

Some important aspects in testing high-modulus fiber composite tubes in axial tension.

Tubular specimens were potted in metal grips to determine the feasibility of this gripping method in applying multiaxial loads. Strain gage rosettes were used to assess grip transitional strains, through thickness strain variation, and strain variations along the tube length and circumference. The investigation was limited to loading graphite/epoxy and glass/epoxy tubes in axial tension. Results include modifications made to the grips to reduce transitional strains, illustrations of the tube failure modes, and some material properties. The gripping concept shows promise as a satisfactory technique for applying multiaxial loads to high-strength, high-modulus fiber composite tubes.

Sullivan, T. L.↗

NASA NTRS1977

Elastohydrodynamic lubrication of elliptical contacts for materials of low elastic modulus. 1: Fully flooded conjunction

Elastohydrodynamic lubrication concepts of conjunctions of elliptical form are applied to materials of low elastic modulus. The influence of the ellipticity parameter and the dimensionless speed, load, and material parameters on minimum film thickness for these materials has been investigated. The ellipticity parameter was varied from a ball on plate configuration to a configuration approaching a line contact. The dimensionless speed and load parameters were varied by 1 order of magnitude. Seventeen different cases were used to generate minimum and central film thickness relations. Contour plots are presented that illustrate the pressure distribution and film thickness in the conjunction.

Hamrock, B. J.↗

NASA NTRS1977

Application of diffusion barriers to high modulus fibers

Barrier layers were coated onto high-modulus fibers, and nickel and titanium layers were overcoated as simulated matrix materials. The objective was to coat the high-strength fibers with unreactive selected materials without degrading the fibers. The fibers were tungsten, niobium, and single-crystal sapphire, while the materials used as barrier coating layers were Al2O3, Y2O3, TiC, ZrC, WC with 14% Co, and HfO2. An ion-plating technique was used to coat the fibers. The fibers were subjected to high-temperature heat treatments to evaluate the effectiveness of the barrier layer in preventing fiber-metal interactions. Results indicate that Al2O3, Y2O3, and HfO2 can be used as barrier layers to minimize the nickel-tungsten interaction. Further investigation, including thermal cycling tests at 1090 C, revealed that HfO2 is probably the best of the three.

Veltri, R. D.↗

NASA NTRS1979

Dynamic measurement of bulk modulus

Technique based on measuring phase difference between microwave reference and test signals and has been used to determine change in bulk modulus of solid-fuel rocket propellants should be useful in studying other dielectric materials.

Dowler, W. L.↗

NASA NTRS1978

Elastohydrodynamic lubrication of elliptical contacts for materials of low elastic modulus. 2: Starved conjunction

Lubricant starvation effects on minimum film thickness for low-elastic modulus materials are studied by moving the inlet boundary closer to the contact center. Contour plots of the pressure and film thickness in and around the contact were obtained for fully flooded and starved lubrication conditions. These contour plots show that the inlet pressure contours become less circular and that the film thickness decreases substantially as the severity of starvation increases.

Hamrock, B. J.↗

NASA NTRS1977

Elastohydrodynamic lubrication of elliptical contacts for materials of low elastic modulus. I - Fully flooded conjunction

A complete numerical solution is presented to the problem of isothermal elastohydrodynamic lubrication of elliptical contacts for low-elastic-modulus materials operating under fully loaded conditions. No assumption is made for the pressure or film thickness within the contact, and compressibility and viscous effects are taken into account. Because of the dimensionless representation of the coordinates, the actual Hertzian contact ellipse becomes a circle regardless of the value of the ellipticity parameter. A minimum-film-thickness relation and a central-film-thickness relation are derived from examining 17 different cases. Contour plots for detailed illustration of the pressure distribution and film thickness in the conjunction are provided.

Hamrock, B. J.↗

NASA NTRS1979

High temperature dynamic modulus and damping of aluminum and titanium matrix composites

Dynamic modulus and damping capacity property data were measured from 20 to over 500 C for unidirectional B/Al (1100), B/Al (6061), B/SiC/Al (6061), Al2O3/Al, SiC/Ti-6Al-4V, and SiC/Ti composites. The measurements were made under vacuum by the forced vibration of composite bars at free-free flexural resonance near 2000 Hz and at amplitudes below 0.000001. Whereas little variation was observed in the dynamic moduli of specimens with approximately the same fiber content (50 percent), the damping of B/Al composites was found at all temperatures to be significantly greater than the damping of the Al2O3/Al and SiC/Ti composites. For those few situations where slight deviations from theory were observed, the dynamic data were examined for information concerning microstructural changes induced by composite fabrication and thermal treatment. The 270 C damping peak observed in B/Al (6061) composites after heat treatment above 460 C appears to be the result of a change in the 6061 aluminum alloy microstructure induced by interaction with the boron fibers. The growth characteristics of the damping peak suggest its possible value for monitoring fiber strength degration caused by excess thermal treatment during B/Al (6061) fabrication and use.

Dicarlo, J. A.↗

NASA NTRS1978

Elastohydrodynamic lubrication of elliptical contacts for materials of low elastic modulus. II - Starved conjunction

The study evaluates the effect of lubricant starvation on minimum film thickness in starved elliptical elastohydrodynamic conjunctions for materials of low elastic modulus. Lubricant starvation is studied simply by moving the inlet boundary closer to the center of the conjunction. A simple expression is presented for the dimensionless inlet boundary distance; this inlet boundary distance defines whether a fully flooded or a starved condition exists in the conjunction. A formula for the minimum film thickness under the starvation condition is derived. Contour plots of the pressure and film thickness in and around the contact are presented for both the fully flooded and starved lubrication conditions. It is shown that the inlet pressure contours become less circular and that the film thickness decreases substantially with increasing starvation severity.

Hamrock, B. J.↗

NASA NTRS1979

High temperature dynamic modulus and damping of aluminum and titanium matrix composites

Dicarlo, J. A.↗

NASA NTRS1980

Fracture modes of high modulus graphite/epoxy angleplied laminates subjected to off-axis tensile loads

Angelplied laminates of high modulus graphite fiber/epoxy were studied in several ply configurations at various tensile loading angles to the zero ply direction in order to determine the effects of ply orientations on tensile properties, fracture modes, and fracture surface characteristics of the various plies. It was found that fracture modes in the plies of angleplied laminates can be characterized by scanning electron microscope observation. The characteristics for a given fracture mode are similar to those for the same fracture mode in unidirectional specimens. However, no simple load angle range can be associated with a given fracture mode.

Sinclair, J. H.↗

NASA NTRS1980

Dynamic Modulus and Damping of Boron, Silicon Carbide, and Alumina Fibers

The dynamic modulus and damping capacity for boron, silicon carbide, and silicon carbide coated boron fibers were measured from-190 to 800 C. The single fiber vibration test also allowed measurement of transverse thermal conductivity for the silicon carbide fibers. Temperature dependent damping capacity data for alumina fibers were calculated from axial damping results for alumina-aluminum composites. The dynamics fiber data indicate essentially elastic behavior for both the silicon carbide and alumina fibers. In contrast, the boron based fibers are strongly anelastic, displaying frequency dependent moduli and very high microstructural damping. Ths single fiber damping results were compared with composite damping data in order to investigate the practical and basic effects of employing the four fiber types as reinforcement for aluminum and titanium matrices.

Dicarlo, J. A.↗

NASA NTRS1980

Fracture modes of high modulus graphite/epoxy angleplied laminates subjected to off-axis tensile loads

Angleplied laminates of high modulus graphite fiber/epoxy were examined in several ply configurations at various tensile loading angles to the zero ply direction to determine the effects of ply orientations on tensile properties, fracture modes, and fracture surface characteristics of the various plies. Experimental results consist of stress-strain data, selected plots, fracture stresses and strains, and scanning electron microscope (SEM) photographs of fracture surfaces. It was found that the stress-strain curves were linear to fracture, and that although fracture surface characteristics for a given fracture mode are similar to those for the same fracture mode in uniaxial specimens, no simple load angle range can be associated with a given fracture mode. It was also concluded that SEM results must be supplemented with ply stress calculations in order to identify ranges of fracture modes occurring as a function of ply orientation with respect to the load direction.

Sinclair, J. H.↗

NASA NTRS1980

Dynamic modulus and damping of boron, silicon carbide, and alumina fibers

The dynamic modulus and damping capacity for boron, silicon carbide, and silicon carbide-coated boron fibers were measured from -190 to 800 C. The single fiber vibration test also allowed measurement of transverse thermal conductivity for the silicon carbide fibers. Temperature-dependent damping capacity data for alumina fibers were calculated from axial damping results for alumina-aluminum composites. The dynamic fiber data indicate essentially elastic behavior for both the silicon carbide and alumina fibers. In contrast, the boron-based fibers are strongly anelastic, displaying frequency-dependent moduli and very high microstructural damping. The single fiber damping results were compared with composite damping data in order to investigate the practical and basic effects of employing the four fiber types as reinforcement for aluminum and titanium matrices.

Dicarlo, J. A.↗

NASA NTRS1981

Modulus, strength and thermal exposure studies of FP-Al2O3/aluminum and FP-Al2O3/magnesium composites

The mechanical properties of FP-Al2O3 fiber reinforced composites prepared by liquid infiltration techniques are improved. A strengthening addition, magnesium, was incorporated with the aluminum-lithium matrix alloy usually selected for these composites because of its good wetting characteristics. This ternary composite, FP-Al2O3/Al-(2-3)Li-(3-5)Mg, showed improved transverse strength compared with FP-Al2O3/Al-(2-3)Li composites. The lower axial strengths found for the FP-Al2O3/Al-(2-3)Li-(3-5)Mg composites were attributed to fabrication related defects. Another technique was the use of Ti/B coated FP-Al2O3 fibers in the composites. This coating is readily wet by molten aluminum and permitted the use of more conventional aluminum alloys in the composites. However, the anticipated improvements in the axial and transverse strengths were not obtained due to poor bonding between the fiber coating and the matrix. A third approach studied to improve the strengths of FP-Al2O3 reinforced composites was the use of magnesium alloys as matrix materials. While these alloys wet fibers satisfactorily, the result indicated that the magnesium alloy composites used offered no axial strength or modulus advantage over FP-Al2O3/Al-(2-3)Li composites.

Bhatt, R. T.↗