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At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Determination of Material Properties Near the Glass Transition Temperature for an Isogrid Boom

Experiments were performed and results obtained to determine the temperature dependence of the modulus of elasticity for a thermoplastic isogrid tube. The isogrid tube was subjected to axial tensile loads of 0-100 lbf and strain was measured at room and elevated temperatures of 100, 120, 140, 160, 180, 190, and 200 F. These were based on tube manufacturer specifying an incorrect glass transition temperature of 210 F. Two protocols were used. For the first protocol the tube was brought to temperature and a tensile test performed. The tube was allowed to cool between tests. For the second protocol the tube was ramped to the desired test temperature and held. A tensile test was performed and the tube temperature ramped to the next test temperature. The second protocol spanned the entire test range. The strain rate was constant at 0.008 in/min. Room temperature tests resulted in the determination of an average modulus of 2.34 x 106 Psi. The modulus decreased above 100 F. At 140 F the modulus had decreased by 7.26%. The two test protocols showed good agreement below 160 F. At this point the glass transition temperature had been exceeded. The two protocols were not repeated because the tube failed.

Blandino, Joseph R.↗
NASA NTRS1988

A fundamental approach to the sticking of insect residues to aircraft wings

The aircraft industry is concerned with the increase of drag on planes due to the sticking of insects on critical airfoil areas. The objectives of the present study were to investigate the effects of surface energy and elasticity on the number of insects sticking onto the polymer coatings on a modified aircraft wing and to determine the mechanism by which insects stick onto surfaces during high velocity impact. Analyses including scanning electron microscopy, electron spectroscopy for chemical analysis and contact angle measurements of uncoated and polymer coated aluminum surfaces were performed. A direct relation between the number of insects sticking on a sample and its surface energy was obtained. Since the sticky liquid from a burst open insect will not spread on the low energy surface, it will ball up providing poor adhesion between the insect debris and the surface. The incoming air flow can easily blow off the insect debris and thus reducing the number of insects that remain stuck on the surface. Also a direct relation between the number of insect sticking onto a surface and their modulus of elasticity was obtained.

Yi, O.↗
NASA NTRS1967

Ceramic research

Load measuring equipment for mechanical testing facility

LOAD TESTING MACHINE↗
NASA NTRS1972

A monostrain test apparatus

Test apparatus is designed for determining tensile strength, modulus of elasticity, elongation, and thermal coefficient of contraction or expansion of uniformly shaped plastics, adhesives, and foam materials over temperature range of 700 to 90 K (800 to -300). Tests may be used in design quality control, and in evaluation of new adhesives and plastic materials.

Helf, J. C.↗
NASA NTRS1971

Statistical analysis of the modal properties of large structural systems.

A theory is developed to predict eigenvalue and eigenvector uncertainty in large dynamic models. The uncertainty is based on physical property uncertainty and should not be confused with numerical roundoff, although the method can be extended to include the latter. The theory, when implemented on a computer, is used to analyze the uncertainties in frequencies and mode shapes based on uncertainties in mass, stiffness, modulus of elasticity, etc. The method incorporates a linear statistical model which is quite adequate for handling property uncertainties of 10% or more. The model is not limited to small systems but uses certain statistical assumptions as well as selective matrix manipulations to keep the size of all matrix operations to within the number of degrees of freedom of the system. Examples are given for two longitudinal vibration problems, and the results are supported by a Monte Carlo analysis.

Collins, J. D.↗
NASA NTRS1972

Soil mechanical properties at the Apollo 14 site.

The Apollo 14 lunar landing provided a greater amount of information on the mechanical properties of the lunar soil than previous missions. Measurements on core-tube samples and the results of transporter track analyses indicate that the average density of the soil in the Fra Mauro region is in the range from 1.45 to 1.60 g/cu cm. The soil strength appears to be higher in the vicinity of the site of the Apollo 14 lunar surface experiments package, and trench data suggest that strength increases with depth. Lower-bound estimates of soil cohesion give values of 0.03 to 0.10 kN/sq m, which are lower than values of 0.35 to 0.70 kN/sq m estimated for soils encountered in previous missions. The in situ modulus of elasticity, deduced from the measured seismic-wave velocity, is compatible with that to be expected for a terrestrial silty fine sand in the lunar gravitational field.

Mitchell, J. K.↗
NASA NTRS1972

Improvement of Reusable Surface Insulation (RSI) materials

The mullite fiber based hardened compacted fibers (HCF) type of reusable surface insulation was further developed for use in the Space Shuttle Program. Two hundred fifty formulations of fiber mixtures, fillers, binders, and organic processing aids were made using mullite fibers as the basic ingredient. Most of the work was accomplished on 15-lb/cu ft material. It was established that higher density materials are stronger with strength values as high as 250 lb/sq in. in tension. New measurement techniques and equipment were developed for accurate determination of strength and strain to failure. Room temperature to 2300 F stress-strain relationships were made. The room temperature tensile modulus of elasticity is 61,700 lb/sq in. and the strain at failure is 0.165 percent, typically, when measured longitudinally parallel to the long axes of the fibers. Thermal insulating effectiveness was increased 20 percent by reducing the diameter of some of the fibers in the material. Improvements were made in density uniformity and strength uniformity in a block of HCF by mixing improvements and by the use of organic additives. Specifications were established on the materials and processes used in making the insulation.

Blome, J. C.↗