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At least 1,621 records · Page 90
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

N2 pressure - broadened O3 line widths and strengths near 1129.4 cm-1

A Beer's Law experiment was performed with a tunable diode laser to find the N2 pressure broadening characteristics of a single 03 absorption line at 1129.426 cm for N2 pressures from 10 to 100 torr (O3 pressure = 3.16 torr). SO2 line positions were used for wavelength calibration. Line shapes were interatively fitted to a Lorentz function. Results were delta (HWHM in MHz) = 47.44 (+ or - 5.34) MHz + 1.730 (+ or - 0.088) MHz/torr *p(torr) with sigma = 0.9897. This intercept compares well with the Doppler O3 - O3 broadened (at 3.16 torr) width of 44.52 Hz. This result in a HWHM line width of 0.44 cm atm at 760 torr and 285 K. The line strengths integrated over delta nu = 0.55 cm were found to be N2 pressure dependent.

Copeland, G. E.↗
NASA NTRS1982

Hot isostatically pressed manufacture of high strength MERL 76 disk and seal shapes

The feasibility of using MERL 76, an advanced high strength direct hot isostatic pressed powder metallurgy superalloy, as a full scale component in a high technology, long life, commercial turbine engine were demonstrated. The component was a JT9D first stage turbine disk. The JT9D disk rim temperature capability was increased by at least 22 C and the weight of JT9D high pressure turbine rotating components was reduced by at least 35 pounds by replacement of forged Superwaspaloy components with hot isostatic pressed (HIP) MERL 76 components. The process control plan and acceptance criteria for manufacture of MERL 76 HIP consolidated components were generated. Disk components were manufactured for spin/burst rig test, experimental engine tests, and design data generation, which established lower design properties including tensile, stress-rupture, 0.2% creep and notched (Kt = 2.5) low cycle fatigue properties, Sonntag, fatigue crack propagation, and low cycle fatigue crack threshold data. Direct HIP MERL 76, when compared to conventionally forged Superwaspaloy, is demonstrated to be superior in mechanical properties, increased rim temperature capability, reduced component weight, and reduced material cost by at least 30% based on 1980 costs.

Eng, R. D.↗
NASA NTRS1982

Prediction of residual tensile strength of transversely impacted composite laminates

The response to low velocity impact of graphite-epoxy T300/5208 composite laminates is discussed. Steel balls of 3/8 inch, 5/8 inch, and 1 inch diameter were the projectiles. Impact energy was limited to 1.2 joules. Impacted specimens were ultrasonically C scanned to determine the impact damaged region. The threshold value of impact energy for impact damage was found to be approximately 0.3 joules. A model was developed to predict the tensile residual strength of impact damaged specimens from fracture mechanics concepts. Impacted specimens were tested in tension to provide a fracture data base. The experimental results agreed well with the predictions from fracture mechanics. In this study, the maximum impact velocity used to simulate the low velocity transverse impact from common objects like tool drops was 10 m/s.

Lal, K. M.↗
NASA NTRS1981

Measurement of the oscillator strengths and autoionization widths of the neutral-aluminum multiplet 3s2 3p2 P0 - 3s 3p2 2P

The hook method is used in conjunction with absorption equivalent width measurements to determine the oscillator strengths and line widths of the Al I multiplet 3s2 3p2 P0 - 3s 3p2 2P at 176 nm. Autoionization is found to be the dominant decay channel for the two levels of the 3p2 2P term, with autoionizing widths of 4.0 and 0.87 x 10 to the 10th/sec for J of 3/2 and 1/2, respectively. The van der Waals scattering cross section for the Al I transition at 176.91 nm by He is determined to be (1.3 + or - 0.3) x 10 to the -14th sq cm at 2400 K, and a solar spectrum calculation centered at 176 nm shows that the Al I features are possible diagnostic probes of (1) solar non-LTE processes, and (2) the temperature minimum and structure of the lower chromosphere.

Lombardi, G. G.↗
NASA NTRS1982

Effect of orthotropic properties and panel width on the compression strength of graphite-epoxy laminates with holes

An experimental study conducted to evaluate the effect of laminate orthotropic properties and panel width on the compression strength of 48-ply graphite-epoxy laminates with drilled holes is described. The test results are evaluated on the basis of hole size and specimen width and are used in determining parameters necessary for predicting trends using the point stress failure criterion. Good agreement is obtained between experimental and predicted values of failure for panels fabricated from two quasi-isotropic laminates and one orthotropic laminate. The results suggest that panels of different widths having holes that are large in relation to the failure prediction parameter should be included in any test program conducted to develop prediction trends that may be used in design applications.

Rhodes, M. D.↗
NASA NTRS1982

Pole-strength of the earth from Magsat and magnetic determination of the core radius

A model based on two days of Magsat data is used to numerically evaluate the unsigned magnetic flux linking the earth's surface, and a comparison of the 16.054 GWb value calculated with values from earlier geomagnetic field models reveals a smooth, monotonic, and recently-accelerating decrease in the earth's pole strength at a 50-year average rate of 8.3 MWb, or 0.052%/year. Hide's (1978) magnetic technique for determining the radius of the earth's electrically-conducting core is tested by (1) extrapolating main field models for 1960 and 1965 downward through the nearly-insulating mantle, and then separately comparing them to equivalent, extrapolated models of Magsat data. The two unsigned fluxes are found to equal the Magsat values at a radius which is within 2% of the core radius; and (2) the 1960 main field and secular variation and acceleration coefficients are used to derive models of 1930, 1940 and 1950. The same core magnetic radius value, within 2% of the seismic value, is obtained. It is concluded that the mantle is a nearly-perfect insulator, while the core is a perfect conductor, on the decade time scale.

Voorhies, G. V.↗
NASA NTRS1982

ISEE-1 and -2 observations of magnetic field strength overshoots in quasi-perpendicular bow shocks

According to the Rankine-Hugoniot jump conditions, the magnetic field strength increases in passing from upstream to downstream of a magnetohydrodynamic shock. At the earth's bow shock the magnetic field often increases significantly more than is required by the Rankine-Hugoniot conditions before decaying in an oscillatory fashion to its downstream average value. Recent OGO-5 and ISEE studies, together with the realization that overshoots also occur in the bow shocks of Venus, Jupiter, and Saturn have focussed attention on these phenomena. It is found that none of the nonlinear dispersive wave theories in the shock literature can account for the overshoot. The present investigation documents the dependence of the overshoot amplitude and thickness on solar wind parameters. Magnetic field overshoots are found to be characteristic of supercritical quasi-perpendicular shocks. The overshoot thickness scales as the ion Larmor radius based upon the solar wind speed and magnetic field.

Livesey, W. A.↗
NASA NTRS1983

Curved Caps Raise Corrugation Strength

Construction concept increases strength-to-weight ratio of corrugated panels. Flat caps are replaced by curved caps in new concept for constructing corrugated panels. Geometry utilizes curved cap for wider cap/web attachment. Beading web prevents local buckling in web while allowing maximum separation between cap strips. Geometry offers significant weight saving over conventional geometry for wide range of loading.

Davis, R. C.↗
NASA NTRS1982

The strength and ductility of polycrystalline NiAl in tension

Experiments at temperatures from 20 C to 400 C at two strain rates (.0001/s and .000005/s) establish that: (1) at room temperatures, binary and microalloyed ( 1000 ppm La, Y, Mo, Ti) NiAl shows negligible ductility, independent of grain size over the range 5 to 140 micrometers; (2) at 295 C the tensile elongation of binary 51 Ni/49 Al increases from 1% to about 5% upon decreasing the grain size to below approximately 10 micrometers; (3) similarly, at 400 C the ductility increases from about 2% to 15% upon decreasing the grain size to below 15 micrometers; (4) the ductility of fine grained (7 micrometer) binary aggregates deformed at 295 C increases from approximately 5% to 12% upon decreasing the strain rate from .0001/s to .000005/s; (5) partial recrystallization (10% to 20%) of warm extruded binary and microalloyed material imparts 1% to 2% ductility at room temperature where fully recrystallized material is brittle; (6) the yield strength obeys a Hall-Petch relationship; and (7) when ductility is not observed, fracture coincides with yielding. The mechanisms underlying the flow and fracture of NiAl are discussed in terms of the nucleation and growth of microcracks. The concept of a critical grain size is considered in the light of the results.

Schulson, E. M.↗
NASA NTRS1982

Graphite fiber surface treatment to improve impact strength and fracture resistance in subsequent composites

Graphite (or carbon) fiber composite impact strength improvement was attempted by modifying the fiber surface. Elastomeric particles were made into lattices and deposited ionically on surface treated graphite fiber in an attempt to prepare a surface containing discrete rubber particles. With hard, nonelastomeric polystyrene discrete particle coverage was achieved. All the elastomeric containing lattices resulted in elastomer flow and filament agglomeration during drying.

Paul, J. T., Jr.↗
NASA NTRS1982

Reinforcing aluminum alloys with high strength fibers

A study is made of the possibility of reinforcing aluminum and aluminum based alloys with fibers made of high strength steel wire. The method of introducing the fibers is described in detail. Additional strengthening by reinforcement of the high alloy system Al - An - Mg was investigated.

Kolpashnikov, A. I.↗
NASA NTRS1982

Strength criteria for composite materials (a literature survey)

Literature concerning strength (failure) criteria for composite materials is reviewed with emphasis on phenomenological failure criteria. These criteria are primarily intended to give a good estimation of the safety margin with respect to failure for arbitrary multiaxial stress states. The failure criteria do not indicate the types of fracture that will occur in the material. The collection of failure criteria is evaluated for applicability for the glass reinforced plastics used in mine detectors. Material tests necessary to determine the parameters in the failure criteria are discussed.

Roode, F.↗
NASA NTRS1982

Molecular-orbital model for metal-sapphire interfacial strength

Self-consistent-field X-Alpha scattered-wave cluster molecular-orbital models have been constructed for transition and noble metals (Fe, Ni, Cu, and Ag) in contact with a sapphire (Al2O3) surface. It is found that a chemical bond is established between the metal d-orbital electrons and the nonbonding 2p-orbital electrons of the oxygen anions on the Al2O3 surface. An increasing number of occupied metal-sapphire antibonding molecular orbitals explains qualitatively the observed decrease of contact shear strength through the series Fe, Ni, Cu, and Ag.

Johnson, K. H.↗
NASA NTRS1981

Detection of strength limiting defects in cellular glasses by dielectric measurements

The foamed glasses that are being considered for structural support in solar thermal energy system silvered glass concentrator mirrors are assessed for strength-limiting defects by a nondestructive technique which measures the capacitance of well defined regions. The feasibility of locating large defects is demonstrated for the case of one type of cellular mass. Observed capacitance variations are believed to be due to small voids or other irregularities in the material. If the defects are equal to or greater than approximately 20 times the glass matrix pore size, they can be resolved with sufficient accuracy to delineate their spatial extent.

Gammell, P. M.↗
NASA NTRS1983

Real line strength distributions for random band models

An improved random band-model method, which makes allowance for the real line-strength distribution, is proposed. The model is shown to be useful for low-resolution, infrared observational data of the outer solar system. The method can be used as easily as conventional random band calculations. In the illustrative examples cited here, the variation of line width with J, the rotational quantum number, is small. Other effects which can, in principle, cause the model to deviate from laboratory observations are discussed. These include the assumption that line positions are random, ignoring the effects of the Lorentz wings of lines immediately outside the specific interval for which the mean transmission is calculated, and ignoring the effects of instrumental slit functions.

Kim, S. J.↗
NASA NTRS1983

Strength and fracture toughness of reaction-bonded Si3N4

Fracture strength and fracture toughness measurements were made on reaction-bonded Si3N4 materials with a range of alpha/beta ratios. The results do not indicate any clear relation between the modulus of rupture and the alpha/beta ratio over the range 1.5-9. Values for the modulus of rupture range from 219 to 290 MN per sq m, with an overall average of 238 MN per sq m. The notched beam fracture toughness is found to be constant over the range of microstructures produced, indicating that of the various microstructural features (e.g., alpha/beta ratio and pore size and distribution) no single element has a controlling influence over fracture toughness and the fracture surface energy.

Danforth, S. C.↗
NASA NTRS1984

Influence of soft inclusions on the strength of wrought materials

The three dimensional soft particles (such as sulfides, silicates and voids) present in most materials are modelled by circular voids in sheet metal. Relationships are sought between the shape and orientation of a hole after rolling and testing in tension. Then, the effect of hole shape and size on mechanical properties is considered experimentally. The presence of voids has a negligible influence on the ultimate tensile stress of ductile materials based on the unperforated area because plastic flow neutralizes the stress intensification present in the elastic region. However, the shape and orientation of the defects are found to play an important role relative to strain at fracture. In certain engineering applications the strain at fracture is more important than the stress at fracture and in this sense the presence of voids are considered to influence the strength of a ductile material.

Pai, D. M.↗