SEARCH · Search NASA
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Mixture of uranium oxide, niobium oxide, and graphite of various carbon-to-oxygen ratios is heated to a temperature below the melting point of the noibium-uranium alloy. The alloy is produced by this method with voids predetermined as to size and total volume.
Substructural void formation in tungsten powder metallurgy as function of annealing temperature for doped, undoped and electron beam melted material
Cu-Ni diffusion couples voids and edges effect on concentration gradients measurement by electron probe microanalysis
Method and photodetector device for locating abnormal voids in low density materials
Development of an advanced A-type polyimide, which can be used to produce autoclave molded, low-void content composites suitable for use at temperatures up to 316 C is reported. It consists of a mixture of methyl nadic anhydride, an 80:20 molar ratio of methylene dianaline and thiodianilene, and pyromellitic dianhydride.
Experimental studies are described in which new A-type polyimide prepolymer chemical modifications were investigated with the aim of increasing the melt phase duration and temperature range permitting autoclave processing, yet retaining the addition-type cure mechanism required for low-void content composites. Several modification candidates were examined, and one specific formulation was selected for detailed investigation. This A-type polyimide prepolymer formulation is shown to possess the desired characteristics.
Layup technique involving repositioning of filler plies and redesigning of bleeder pressure pad reduces wrinkles, voids, pores, and other defects at sharp bends in laminated materials.
Proposed tool forces adhesive into cracks. After inlet and outlet holes have been drilled to proper depth, alinement pin is inserted in inlet hole. Adhesive fills void or is forced into delamination, expanding delamination slightly to ensure full penetration. Potential applications in repair of fiber-reinforced components, boats, storage tanks, and some automobile bodies.
Need for lightweight materials as structural components for future space transportation systems stimulated development of systematic method for manufacturing a polyimide/graphite composite. Laminates manufactured by process are void-free, exhibit excellent thermo-oxidative stability up to 315 degrees C (600 degrees F) and are 40 percent lighter than aluminum. Process is precise, repeatable, and ideally suited for researchers and small-lot producers of composite materials.
The internal microstructure and growth kinetics of Al2O3 scales on Ni-15Cr-13Al (wt percent) are investigated by TEM and analyzed in relation to models of diffusivity. Polished arc-melted specimens were oxidized in 1-atm air at 1100 C for 0.1, 1.0, and 20 hours and ion-thinned for TEM at 100 kV. The frequency distribution of void size and grain size is determined for different oxidation times and scale depths. The kinetics of microvoid growth and of grain and scale growth are plotted and related via simplified models to lattice and grain-boundary oxygen diffusivity, respectively. Good agreement is found between model predictions and data obtained by Oishi and Kingery (1960) on oxygen diffusion in bulk Al2O3. The further implications and limitations of these findings are discssed.
A series of photographs taken with Osaka University's high temperature 3MV electron microscope of alpha-A1(z)O(3) at 2000 C is presented. The dynamic study shows grain boundary migration in progress and demonstrates that disappearance of voids is controlled by boundary migration.
Vibration-induced interference fringes reveal locations of defects. Holographic apparatus used to view object while vibrated ultrasonically. Interference fringes in hologram reveal brazing defects. Holographic technique locates small voids in large brazed joints. Identifies unbrazed regions 1 in. to second power (6 cm to the second power) or less in area.
Unusual heat treatment heals voids in aluminum interconnections on integrated circuits (IC's). Treatment consists of heating IC to temperature between 200 degrees C and 400 degrees C, holding it at that temperature, and then plunging IC immediately into liquid nitrogen. Typical holding time at evaluated temperature is 30 minutes.
The probability that a volume of the universe of given size and shape spaced at random will be void of galaxies is used here to study various models of the origin of cosmological structures. Numerical simulations are conducted on hot-particle and cold-particle-modulated inflationary models with and without biasing, on isothermal or initially Poisson models, and on models where structure is seeded by loops of cosmic string. For the Pisces-Perseus redshift compilation of Giovanelli and Haynes (1985), it is found that hierarchical scaling is obeyed for subsamples constructed with different limiting magnitudes and subsamples taken at random. This result confirms that the hierarchical ansatz holds valid to high order and supports the idea that structure in the observed universe evolves by a regular process from an almost Gaussian primordial state. Neutrino models without biasing show the effect of a strong feature in the initial power spectrum. Cosmic string models do not agree well with the galaxy data.
Two reports describe experimental studies of efficacy of radiographic detection of voids in "green" (unfired) and sintered SiC and SiN ceramics. Projection radiography provides greater sensitivity of detection. Studies motivated by need for nondestructive technique to detect flaws limiting strengths of sintered structural ceramic components.
Clustering properties of two samples from the CfA redshift survey, each containing about 2500 galaxies, are studied. A comparison of the velocity distributions via a K-S test reveals structure on scales comparable with the extent of the survey. The void probability function (VPF) is employed for these samples to examine the structure and to test for scaling relations in the galaxy distribution. The galaxy correlation function is calculated via moments of galaxy counts. The shape and amplitude of the correlation function roughly agree with previous determinations. The VPFs for distance-limited samples of the CfA survey do not match the scaling relation predicted by the hierarchical clustering models. On scales not greater than 10/h Mpc, the VPFs for these samples roughly follow the hierarchical pattern. A variant of the VPF which uses nearly all the data in magnitude-limited samples is introduced; it accounts for the variation of the sampling density with velocity in a magnitude-limited survey.
Luminosities of H alpha emission from a pair of interacting galaxies in the low density environment of the Bootes void are presented. CG 692 (IRAS 1519+5050) has an H alpha luminosity of 2 x 10(exp 42) ergs s(exp -1), indicating a star formation rate of 18.4 solar mass yr(exp -1). Individual extranuclear H alpha regions have luminosities of approximately 10(exp 40) ergs s(exp -1). These luminosities are similar to those found for H II regions in bright, late-type galaxies in more densely populated parts of the Universe.
Internal and surface voids of known sizes incorporated into silicon carbide and silicon nitride ceramic reference specimens at prescribed locations. Specimens used to demonstrate sensitivity and resolution in nondestructive examination techniques like scanning laser acoustic microscopy and x-radiography, and to assist in establishing proper examination procedures.