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At least 91 records · Page 5
All sourcesNASA NTRSDOE OSTI
NASA NTRS1955

Investigation of a Cermet Gas-turbine-blade Material of Titanium Carbide Infiltrated with Hastalloy C

A cermet composition was investigated as a potential material for gas-turbine blades. Blades of HS-21 alloy were also operated in the engine simultaneously to provide a basis of comparison. The cermet blades survived as long as approximately 312-1/2 hours at about 1500 degrees F with an average midspan centrifugal stress of approximately 11,500 psi. The alloy blade midspan stress was about 15,300 psi. Because of extensive damage to both types of blade due to external causes, a reliable comparison of operating lives could not be made. The cermet blades tended to fail in the airfoil rather than in the base, although the base was the usual location of failure in a prior study of cold-pressed and sintered cermets of other compositions with the same blade shape.

Hoffman, Charles A↗
NASA NTRS1993

Polymer infiltration studies

During the past three months, significant progress has been made on the preparation of carbon fiber composites using advanced polymer resins. The results are set forth in recent reports and publications, and will be presented at forthcoming national and international meetings. Current and ongoing research activities reported herein include: textile composites from powder-coated towpreg; role of surface coating in braiding; prepregger hot sled operation; ribbonizing powder-impregenated towpreg; textile composites from powder-coated towpreg; role of bulk factor powder curtain prepreg process advanced tow placement (ATP) open-section part warpage control. During the coming months research will be directed toward further development of the new powder curtain prepregging method and on ways to customize dry powder towpreg for textile and robotic applications in aircraft part fabrication. Studies of multi-tow powder prepregging and ribbon preparation will be conducted in conjunction with continued development of prepregging technology and the various aspects of composite part fabrication using customized towpreg. Also, during the period ahead work will continue on the analysis of the performance of the new solution prepregger.

Marchello, Joseph M.↗
NASA NTRS1993

Polymer Infiltration Studies

Significant progress has been made on the preparation of carbon fiber composites using advanced polymer resins during the past three months. Current and ongoing research activities reported herein include: (1) Prepregger Hot Sled Operation; (2) Ribbonizing Powder-Impregnated Towpreg; (3) Textile Composites from Powder-Coated Towpreg: Role of Bulk Factor; and (4) Powder Curtain Prepreg Process. During the coming months research will be directed toward further development of the new powder curtain prepregging method and on ways to customize dry powder towpreg for textile and robotic applications in aircraft part fabrication. Studies of multi-tow powder prepregging and ribbon preparation will be conducted in conjunction with continued development of prepegging technology and the various aspects of composite part fabrication using customized towpreg. Also, work will continue on the analysis of the new solution prepegger.

Marchello, Joseph M.↗
NASA NTRS1994

Polymer infiltration studies

During the past three months, significant progress has been made on the preparation of carbon fiber composites using advanced polymer resins. The results are set forth in recent reports and publications, and will be presented at forthcoming national and international meetings. Current and ongoing research activities reported herein include: textile composites from powder-coated towpreg - role of surface coating in braiding; prepregger hot sled operation in making tape from powder coated tow; ribbonizing powder-impregnated towpreg; textile composites from powder-coated towpreg - role of bulk factor in consolidation; powder curtain prepreg process improvements in doctoring of powder; and hot/cold shoe for ATP open-section part warpage control.

Marchello, Joseph M.↗
NASA NTRS1998

Phenylethynyl Containing Polyarylene Ethers/Polyimides Resin Infiltration of Composites

The following tasks were performed at NCA&TSU during the second year in performance of the grant. LaRC-LV-1 13 resin was synthesized at NCA&TSU. In order to perform the synthesis, glassware and needed apparatus were purchased with grant funds along with the appropriate monomers. It was found that the LaRC-LV-1 13 resin was easily synthesized by the NMP solvent/toluene imminization/distilled water precipitation process. However, in use this resin exhibited a bubbling/foaming behavior during cure that was detrimental leading to the production of composite panels having a high void content. Composite panels were fabricated using compression molding and resin transfer molding (RTM) techniques. Initial fiber volume determinations were computed at NCA&TSU along with NASA-Langley measured c-scans on the panels produced. The initial results indicated a unsatisfactory level of approximately 20% by volume of voids. Testing of uniaxial coupons in compression to failure also agreed with these results. The uniaxial coupons delaminated as the major mode of failure indicative of an unacceptably low level of resin and to much void content in the final composites produced. In discussions with Dr. Brian Jensen, it was suggested the void fraction needs to be reduced to at least 2% by volume for a useful composite. The panels produced used both resin synthesized at NASA-Langley and NCA&TSU. In reviewing our progress over the past year, it was noted that the resin as formulated by the current synthesis process bubbled at elevated temperature. This was especially observed in neat resin slugs cured at the recommended one, four and eight hour cure temperatures. Pressurized cures where then performed with pressures up to 200 psi and simultaneously the lowest eight hour cure temperatures. Although this procedure reduced the amount of bubbles to some extent in the neat resin slugs it did not completely eliminate them. The cure reaction appears to be very energetic even at the lowest recommended cure temperature. Currently, the pressurized cure apparatus developed at NCA&TSU is limited to 200 psi.

Dunn, DeRome O.↗
NASA NTRS2000

Silicon Effects on Properties of Melt Infiltrated SiC/SiC Composites

Silicon effects on tensile and creep properties, and thermal conductivity of Hi-Nicalon SiC/SiC composites have been investigated. The composites consist of 8 layers of 5HS 2-D woven preforms of BN/SiC coated Hi-Nicalon fiber mats and a silicon matrix, or a mixture of silicon matrix and SiC particles. The Hi-Nicalon SiC/silicon and Hi-Nicalon SiC/SiC composites contained about 24 and 13 vol% silicon, respectively. Results indicate residual silicon up to 24 vol% has no significant effect on creep and thermal conductivity, but does decrease the primary elastic modulus and stress corresponding to deviation from linear stress-strain behavior.

Bhatt, Ramakrishna T.↗
NASA NTRS2004

Computation of Variability in the Average Thermal and Mechanical Properties of a Melt-infiltrated Sic/sic Composite

Thermal conductivity and tensile properties (elastic modulus, proportional limit strength, inplane tensile strength, and strain to failure) of a SiC/SiC composite were experimentally determined at 816 and 1204 C. Tests were performed at room temperature on the same material to obtain interlaminar shear and tensile strength. For each thermal and mechanical property 24 tests were conducted to capture the variation. A random sampling method was used to quantify the variability exhibited by the mean values of the thermal and mechanical properties. The minimum number of tests required to characterize the mean value of each thermal or mechanical property for the composite was determined by varying the group size of the random sample.

Kalluri, Sreeramesh↗
NASA NTRS2000

Article and method for making complex shaped preform and silicon carbide composite by melt infiltration

Small diameter silicon carbide-containing fibers are provided in a bundle such as a fiber tow that can be formed into a structure where the radii of curvature is not limited to 10-20 inches. An aspect of this invention is directed to impregnating the bundles of fibers with the slurry composition to substantially coat the outside surface of an individual fiber within the bundle and to form a complex shaped preform with a mass of continuous fibers.

Steibel, James D.↗
NASA NTRS2001

Article and method for making complex shaped preform and silicon carbide composite by melt infiltration

Small diameter silicon carbide-containing fibers are provided in a bundle such as a fiber tow that can be formed into a structure where the radii of curvature is not limited to 10-20 inches. An aspect of this invention is directed to impregnating the bundles of fibers with the slurry composition to substantially coat the outside surface of an individual fiber within the bundle and to form a complex shaped preform with a mass of continuous fibers.

Steibel, James D.↗
NASA NTRS1993

Thermal and hydraulic considerations regarding the fate of water discharged by the outflow channels to the Martian northern plains

The identification of possible shorelines in the Martian northern plains suggests that the water discharged by the circum-Chryse outflow channels may have led to the formation of transient seas, or possibly even an ocean, covering as much as one-third of the planet. Speculations regarding the possible fate of this water have included local ponding and reinfiltration into the crust; freezing, sublimation, and eventual cold-trapping at higher latitudes; or the in situ survival of this now frozen water to the present day -- perhaps aided by burial beneath a protective cover of eolian sediment or lavas. Although neither cold-trapping at higher latitudes nor the subsequent freezing and burial of flood waters can be ruled out, thermal and hydraulic considerations effectively eliminate the possibility that any significant reassimilation of this water by local infiltration has occurred given climatic conditions resembling those of today. The arguments against the local infiltration of flood water into the northern plains are two-fold. First, given the climatic and geothermal conditions that are thought to have prevailed on Mars during the Late Hesperian (the period of peak outflow channel activity in the northern plains), the thickness of the cryosphere in Chryse Planitia is likely to have exceeded 1 km. A necessary precondition for the widespread occurrence of groundwater is that the thermodynamic sink represented by the cryosphere must already be saturated with ice. For this reason, the ice-saturated cryosphere acts as an impermeable barrier that effectively precludes the local resupply of subpermafrost groundwater by the infiltration of water discharged to the surface by catastraphic floods. Note that the problem of local infiltration is not significantly improved even if the cryosphere were initially dry, for as water attempts to infiltrate the cold, dry crust, it will quickly freeze, creating a seal that prevents any further infiltration from the ponded water above. The second argument against the local infiltration of flood water in the northern plains is based on hydraulic considerations. Repeated impacts have likely brecciated the Martian crust down to a depth of roughly 10 km. Given a value of permeability no greater than that inferred for the top 10 km of the Earth's crust (approximately 10(exp -2) darcies), a timescale as much as a billion years or more for the Martian groundwater system to achieve hydrostatic equilibrium, and the approximately 2-4 km elevation difference between the outflow channel source regions and the northern plains, the water confined beneath the frozen crust of the northern plains should have been under a significant hydraulic head. Thus, the existence of a hydraulic pathway between the ponded flood waters above the northern plains and the confined aquifer lying beneath it would not have led to the infiltration of flood water back into the crust, but rather the additional expulsion of groundwater onto the surface.

Clifford, S. M.↗
NASA NTRS2007

Rapid Fabrication of Carbide Matrix/Carbon Fiber Composites

Composites of zirconium carbide matrix material reinforced with carbon fibers can be fabricated relatively rapidly in a process that includes a melt infiltration step. Heretofore, these and other ceramic matrix composites have been made in a chemical vapor infiltration (CVI) process that takes months. The finished products of the CVI process are highly porous and cannot withstand temperatures above 3,000 F (approx.1,600 C). In contrast, the melt-infiltration-based process takes only a few days, and the composite products are more nearly fully dense and have withstood temperatures as high as 4,350 F (approx.2,400 C) in a highly oxidizing thrust chamber environment. Moreover, because the melt- infiltration-based process takes much less time, the finished products are expected to cost much less. Fabrication begins with the preparation of a carbon fiber preform that, typically, is of the size and shape of a part to be fabricated. By use of low-temperature ultraviolet-enhanced chemical vapor deposition, the carbon fibers in the preform are coated with one or more interfacial material(s), which could include oxides. The interfacial material helps to protect the fibers against chemical attack during the remainder of the fabrication process and against oxidation during subsequent use; it also enables slippage between the fibers and the matrix material, thereby helping to deflect cracks and distribute loads. Once the fibers have been coated with the interfacial material, the fiber preform is further infiltrated with a controlled amount of additional carbon, which serves as a reactant for the formation of the carbide matrix material. The next step is melt infiltration. The preform is exposed to molten zirconium, which wicks into the preform, drawn by capillary action. The molten metal fills most of the interstices of the preform and reacts with the added carbon to form the zirconium carbide matrix material. The zirconium does not react with the underlying fibers because they are protected by the interfacial material(s). The success of the melt-infiltration step depends on interface material selection and uniform coating of the fibers, infiltration with the correct amount of carbon, and careful control of temperature and rate of heating.

Williams, Brian E.↗