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At least 991 records · Page 55
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Collision strengths for 1199 and 1729 of S III

Collision strengths are calculated for the S III ground state from electron impact excitation in the Io torus. The study is based on data taken at 119.9 nm and 172.9 nm by the IUE spacecraft and with the rocket-borne Faint Object Telescope. The collision strengths of the 3p(2)3P3s3p(3)(5)S(4) and (3)P-3s3p(3)(3)D(0) UV lines are derived from a three-state close coupling aproximation. A Gailitis averaging scheme accounts for resonance effects in the forbidden transition. The calculated intensities of the two transitions at an electron temperature of 80,000 K are in agreement with observed intensities.

Ho, Y. K.↗
NASA NTRS1984

The depletion of pre-interstellar matter and an examination of Ni II oscillator strengths

IUE absorption-line data obtained at 110-320 nm with resolution 10-30 pm toward the B-star component of the multiple system of Alpha Sco are presented in graphs and tables and used to characterize the circumstellar shell around the M1.5 Iab component. Resonant lines of Ni II are identified at strengths in excess of 4 pm and fit to a growth curve constructed using the Fe II, Si II, and Mn II lines, and the results are found to confirm the oscillator strengths determined by Kurucz and Peytremann (1975) to within 50 percent. Shell depletions 2-20 times smaller than those for dense clouds such as the surrounding Oph complex are calculated and attributed to the formation of circumstellar dust. The implications of the results for the condensation of various elements in dense and diffuse clouds are explored.

Cardelli, J. A.↗
NASA NTRS1985

Line positions and strengths of CO2 in the 1200-1430/cm region

A study is reported in which the vibrational rotation spectrum of CO2 in the 1200-1430/cm region has been studied at a 0.005/cm resolution with a Fourier transform spectrometer. The positions and strengths of lines in the 10001-00001 bands of the species 628, 627, and 638 and the 11101-01101 and 11102-01101 bands of 628 have been measured and analyzed. Based on the results obtained, the band center frequencies, upper and lower state vibrational constants, band strengths, and coefficients in the F factor expression are determined.

Toth, R. A.↗
NASA NTRS1985

The influence of lay-up and thickness on composite impact damage and compression strength

The effects of composite stacking sequence, thickness, and percentage of zero-degree plies on the size, shape, and distribution of delamination through the laminate thickness and on residual compression strength following impact were studied. Graphite/epoxy laminates were impacted with an 0.5 inch diameter aluminum sphere at a specific low or high velocity. Impact damage was measured nondestructively by ultrasonic C-scans and X-radiography and destructively by the deply technique, and compression strength tests were performed. It was found that differences in compression failure strain due to stacking sequence were small, while laminates with very low percentages of zero-degree plies had similar failure loads but higher failure strains than laminates with higher percentages of zero-degree plies. Failure strain did not correlate with planar impact damage area, and delaminations in impact regions were associated with matrix cracking.

Guynn, E. G.↗
NASA NTRS1985

Grain refinement of high strength steels to improve cryogenic toughness

Grain-refining techniques using multistep heat treatments to reduce the grain size of five commercial high-strength steels were investigated. The goal of this investigation was to improve the low-temperature toughness as measured by Charpy V-notch impact test without a significant loss in tensile strength. The grain size of four of five alloys investigated was successfully reduced up to 1/10 of original size or smaller with increases in Charpy impact energy of 50 to 180 percent at -320 F. Tensile properties were reduced from 0 to 25 percent for the various alloys tested. An unexpected but highly beneficial side effect from grain refining was improved machinability.

Rush, H. F.↗
NASA NTRS1985

Notched strength of composite laminates: Predictions and experiments - A review

A self-contained review of several semiempirical fracture models for predicting notched strength of composite laminates is presented, based on notched strength data on 70 different laminate configurations of graphite/epoxy, boron/aluminum, and graphite/polyimide. Emphasis is placed on experimental results concerning such failure factors as delamination, splitting, and size of damage zone. Moreover, the fracture model parameters are correlated with the notch sensitivity of composite laminates, and the applicability of the correlations in describing the material notch sensitivity is evaluated. The predictions provided by the different models were found to be identical for all practical purposes.

Awerbuch, J.↗
NASA NTRS1984

Optimization of pin bearing joint strength for segmented graphite/epoxy filament wound case in Space Shuttle

An attempt is made to demonstrate the feasibility of a composite joint in a segmented, graphite/epoxy filament-wound composite case for the Space Shuttle's Solid Rocket Motors. The joint's required ultimate line load is of the of 82,000 lb/in. By optimizing composite layup, and the ratios of pin diameter/specimen thickness, edge distance/pin diameter, and specimen width/pin diameter, a pin bearing joint strength of 85 ksi was obtained. Double pin testing disclosed that the pin close to the composite joint carries a higher load than the outboard pin. Pin bearing strength is noted to vary with matrix resin system.

Munjal, A. K.↗
NASA NTRS1985

On the use of crack-tip-opening displacement to predict the fracture strength of notched graphite/epoxy laminates

Using the center-cracked tension specimen geometry, the fracture strength of notched graphite/epoxy laminates is measured experimentally. Four replicate tests are conducted for a variety of laminate-stacking sequences, thicknesses, and notch lengths. Extensive notch-tip damage prior to fracture is characteristic of most laminates. The values of critical crack-tip-opening displacement (CTOD) are calculated from values of crack-opening displacement measured at the notch center line at failure and are found to be independent of notch size for the laminates studied. A Dugdale (1950) model is used along with the estimated CTOD to predict notched laminate strength.

Harris, C. E.↗
NASA NTRS1985

Strength and flexibility properties of advanced ceramic fabrics

The mechanical properties of four advanced ceramic fabrics are measured at a temperature range of 23 C to 1200 C. The fabrics evaluated are silica, high-and low-boria content aluminoborosilicate, and silicon carbide. Properties studied include fabric break strengths from room temperature to 1200 C, and bending durability after temperature conditioning at 1200 C and 1400 C. The interaction of the fabric and ceramic insulation is also studied for shrinkage, appearance, bend resistance, and fabric-to-insulation bonding. Based on these tests, the low-boria content aluminoborosilicate fabric retains more strength and fabric durability than the other fabrics studied at high temperature.

Sawko, P. M.↗
NASA NTRS1985

Cryogenic insulation strength and bond tester

A method and apparatus for testing the tensile strength and bonding strength of sprayed-on foam insulation attached to metal cryogenic fuel tanks is described. A circular cutter is used to cut the insulation down to the surface of the metal tank to form plugs of the insulation for testing in situ on the tank. The apparatus comprises an electromechanical pulling device powered by a belt battery pack. The pulling device comprises a motor driving a mechanical pulling structure comprising a horizontal shaft connected to two bell cracks which are connected to a central member. When the lower end of member is attached to a fitting, which in turn is bonded to a plug, a pulling force is exerted on the plug sufficient to rupture it. The force necessary to rupture the plug or pull it loose is displayed as a digital read-out.

Schuerer, P. H.↗
NASA NTRS1986

Determination of band oscillator strengths of atmospheric molecules from high resolution vacuum ultraviolet cross section measurements

An account is given of progress in work on (1) the determination of band oscillator strengths of the Schumann-Runge absorption bands of (16)O2 and (18)O2 from cross section measurements conducted at 79 K; (2) the determination of the absolute absorption cross section of the Schumann-Runge bands of (16)O(18)O from optical depth measurements performed on mixtures of (16)O2, (18)O2 and (16)O(18)O at 79K; and (3) the influence of Schumann-Runge linewing contributions on the determination of the Herzberg continuum absorption cross section of (16)O2 in the wavelength region 194 to 204 nm. The experimental investigations are effected at high resolution with a 6.65 m scanning spectrometer which is, by virtue of its small instrumental width (EWHM = 0.0013 nm), uniquely suitable for cross section measurements of molecular bands with discrete rotational structure. Absolute cross sections, which are independent of the instrumental function and from which band oscillator strengths are directly determined, are measured for the absorption bands that are most predissociated. Such measurements are needed for (1) accurate calculations of the stratospheric production of atomic oxygen and heavy ozone formed following the photopredissociation of (18)O(16)O by solar radiation penetrating between the absorption lines of (16)O2; (2) elucidation of the mechanism of predissociation of the upper state of the Schumann-Runge bands; and (3) determination of the true shape of the Herzberg continuum cross section.

Parkinson, W. H.↗
NASA NTRS1986

Effects of external environments on the short beam shear strength of filament wound graphite/epoxy

Filament wound graphite/epoxy samples were immersed in seawater, deionized water, and toluene at room temperature and 80 deg C for 5, 15, and 43 days, and in methanol at room temperature for 15 and 43 days. The percent weight gains and short beam shear strengths were determined after environmental exposure. Samples immersed in deionized water and seawater had higher percent weight gains than those immersed in toluene at room temperature and 80 deg C. The percent weight gains for samples immersed in methanol at room temperature were comparable to those of deionized water and seawater immersed samples. A comparison of percent decreases in short beam shear strengths could not be made due to a large scatter in data. This may indicate defects in samples due to machining or variations in material properties due to processing.

Penn, B. G.↗
NASA NTRS1985

Strength and flexibility properties of advanced ceramic fabrics

The mechanical properties of four advanced ceramic fabrics were measured at a temperature range of 23C to 1200C. The fabrics evaluated were silica, high and low-boria content aluminoborosilicate, and silicon carbide. Properties studied included fabric break strengths from room temperature to 1200C, and bending durability after temperature conditioning at 1200C and 1400C. The interaction of the fabric and ceramic insulation was also studied for shrinkage, appearance, bend resistance, and fabric-to-insulation bonding. Based on these tests, the low-boria content aluminoborosilicate fabric retained more strength and fabric durability than the other fabrics studied at high temperature.

Sawko, P. M.↗
NASA NTRS1986

Evaluation of residual strength of composite laminates damaged by low velocity impacts

This work presents the study of Low Velocity Transverse Impact damage of graphite-epoxy T300/5208 composite material. An energy dissipation model was developed to predict the residual strength from fracture mechanics concepts. The specimens, 100 mm diameter clamped plates, were impact damaged by a cantilever-type instrumented 1-inch diameter steel ball. This study was limited to impact velocity 6 m/sec. Rectangular strips, 50 mm x 125 mm, were cut from the impact-damaged specimens so that the impact damage zone was in the center of the strips. These strips were tested to obtain their residual strength. Predictions were compared with the test results.

Lal, K. M.↗
NASA NTRS1986

Effect of grain-boundary crystallization on the high-temperature strength of silicon nitride

Si3N4 specimens having the composition 88.7 wt pct Si3N4-4.9 wt pct SiO2-6.4 wt pct Y2O3 were sintered at 2140 C under 25 atm N2 for 1 h and then subjected to a 5 h anneal at 1500 C. Crystallization of an amorphous grain-boundary phase resulted in the formation of Y2Si2O7. The short-time 1370 C strength of this material was compared with that of material of the same composition having no annealing treatment. No change in strength was noted. This is attributed to the refractory nature of the yttrium-rich grain-boundary phase (apparently identical in both glassy and crystalline phases) and the subsequent domination of the failure process by common processing flaws.

Pierce, L. A.↗
NASA NTRS1986

Collision strengths for the intercombination lines of S III

The collision strengths of intercombination lines of S III ions observed in the Io torus are calculated on the basis of data gathered by Voyager instruments, the IUE and the Faint Object Telescope. The doubly ionized ions are excited by electron impacts and move from the 3P2P(3) ground state to excited 3s3P3(1)PO, (1)DO, 3p3d(1)PO, and 3p4s(1)PO states. Excitational cross sections are calculated with a two-state close-coupling approximation for the energy range up to 1,000,000 K, with target states being represented by multiconfiguration interaction wave functions. The close-coupling approximation regarded as an accurate technique because of the dominance of the Coulomb factor in the ionized state. The wave function calculations are estimated to yield values accurate to within 30 percent. Further work is need to quantify the magnitude of error introduced by resonance contributions to the collision strengths.

Ho, Y. K.↗
NASA NTRS1986

Strength and microstructure of Si3N4 sintered with ZrO2 additions

Densities greater than 99 percent of theoretical were obtained with stabilized ZrO2 additions to Si3N4. Material sintered at 2140 C under 2.5 MPa nitrogen overpressure with 3.8, 9.9, and 13.4 wt pct ZrO2 had a predominantaly equiaxed grain size ranging from 0.2 to 7.0 microns. At 1370 C, the latter composition exhibited a flexural strength of about 487 MPa, equal to that of a finer-grain-size, hot-pressed Si3N4 + ZrO2 material having excellent high-temperature static fatigue properties. Transmission electron microscopy of the sintered Si3N4 revealed a glassy grain-boundary phase at all three ZrO2 levels and partially crystalline triple points for the 9.9 and 13.4 wt pct ZrO2-containing materials. Slow crack growth was observed for 1370 C flexure tests and correlated with nonlinear load deflection traces for stresses greater than 503 MPa. The crystallization of the grain-boundary glass is insterpreted as beneficial to the attainment of high (1370 C) flexural strength.

Sanders, W. A.↗
NASA NTRS1986

Global atmospheric concentrations and source strength of ethane

A study of the variation in ethane (C2H6) concentration between northern and southern latitudes over three years is presented together with a new estimate of its source strength. Ethane concentrations vary from 0.07 to 2 p.p.b.v. (parts per billion by volume) in air samples collected in remote surface locations in the Pacific (latitude 71 N-47 S) in all four seasons between September 1984 and June 1985. The variations are consistent with southerly transport from sources located chiefly in the Northern Hemisphere, further modified by seasonal variations in the strength of the reaction of C2H6 with OH radicals. These global data can be combined with concurrent data for CH4 and the laboratory reaction rates of each with OH to provide an estimate of three months as the average atmospheric lifetime for C2H6 and 13 + or - 3 Mtons for its annual atmospheric release.

Blake, D. R.↗