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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.

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At least 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
NASA NTRS1978

In situ ply strengths - An initial assessment

The in situ ply strengths in several composites were calculated using a computational procedure developed for this purpose. Laminate fracture data for appropriate low modulus and high modulus fiber composites were used in the laminate analysis in conjunction with the method of least squares. The laminate fracture data were obtained from tests on Modmor-I graphite/epoxy, AS-graphite/epoxy, boron/epoxy and E-glass/epoxy. The results obtained show that the calculated in situ ply strengths can be considerably different from those measured in unidirectional composites, especially the transverse strengths and those in angleplied laminates with transply cracks.

Chamis, C. C.↗
NASA NTRS1977

Pressureless sintered beta-prime-Si3N4 solid solution - Fabrication, microstructure, and strength

Pressureless sintering of beta-prime-Si3N4 solid solution was studied as a function of temperature using Si3N4, A1N, and Al2O3 as basic constituents. Y2O3-SiO2 additions were used to promote liquid-phase sintering. The sintered specimens were characterized with respect to density, microstructure, strength, oxidation, and thermal shock resistance. Density greater than 98 percent of theoretical was achieved by pressureless sintering at 1750 C. The microstructure consisted essentially of fine-grained beta-prime-Si3N4 solid solution as the major phase. Modulus of rupture strengths up to 483 M Pa were achieved at moderate temperature (1000 C), but decreased to 228 M Pa at 1380 C. This substantial strength loss was attributed to a 'glassy' grain boundary phase formed during cooling from the sintering temperature. The best oxidation resistance was exhibited by a composition containing 3 mol % Y2O3-SiO2 additives. Water quench thermal shock resistance was equivalent to that of reaction sintered silicon nitride but lower than hot-pressed silicon nitride.

Dutta, S.↗
NASA NTRS1978

Absorption strength of the perturbed nu-4 band of CH3Cl

The nu-4 band of CH3Cl interacts strongly with the 3 nu-6 band. Levels of both bands are mixed and both appear strongly in absorption. The strengths of both bands have been measured taking into account the mixing of the levels. The absorption strengths of both bands can be related to a single parameter, namely, the strength of the unperturbed nu-4 band. This was calculated to be 41.8 per sq cm/atm at 297 K.

Margolis, J. S.↗
NASA NTRS1978

Reproducibility of structural strength and stiffness for graphite-epoxy aircraft spoilers

Structural strength reproducibility of graphite epoxy composite spoilers for the Boeing 737 aircraft was evaluated by statically loading fifteen spoilers to failure at conditions simulating aerodynamic loads. Spoiler strength and stiffness data were statistically modeled using a two parameter Weibull distribution function. Shape parameter values calculated for the composite spoiler strength and stiffness were within the range of corresponding shape parameter values calculated for material property data of composite laminates. This agreement showed that reproducibility of full scale component structural properties was within the reproducibility range of data from material property tests.

Howell, W. E.↗
NASA NTRS1979

Weld bead reinforcement removal: A method of improving the strength and ductility of peaked welds in 2219-T87 aluminum alloy plate

The results of a study to determine the degree to which the ductility and tensile properties of peaked welds could be enhanced by removing the reinforcing bead and fairing the weld nugget into the adjacent parent metal are presented. The study employed 2219-T87 aluminum alloy plate, tungsten inert gas (TIG) welding, and 2319 filler wire. The study concluded that significant improvements in peak weld, ultimate strength, and ductility can be obtained through removal and fairing of the weld reinforcing bead. The specimens so treated and tested in this program exhibited ultimate strength improvements of 2 to 3 percent for peak angles of 5.8 to 10 degrees and 10 to 22 percent for welds with peak angles of 11.7 to 16.9 degrees. It was also determined that removal of the weld bead enhanced the ability of peaked welds to straighten when exposed to cyclic loading at stress levels above the yield strength.

Lovoy, C. V.↗
NASA NTRS1979

Bend strengths of reaction bonded silicon nitride prepared from dry attrition milled silicon powder

Dry attrition milled silicon powder was compacted, sintered in helium, and reaction bonded in nitrogen-4 volume percent hydrogen. Bend strengths of bars with as-nitrided surfaces averaged as high as 210 MPa at room temperature and 220 MPa at 1400 C. Bars prepared from the milled powder were stronger than those prepared from as-received powder at both room temperature and at 1400 C. Room temperature strength decreased with increased milling time and 1400 C strength increased with increased milling time.

Herbell, T. P.↗
NASA NTRS1978

Yield strengths of flows on the earth, Mars, and moon

Dimensions of flows on the earth, Mars, and moon and their topographic gradients obtained from remote measurements are used to calculate yield strengths with a view to explore the validity of the Bingham plastic model and determine whether there is a relation between yield strengths and silica contents. Other factors are considered such as the vagaries of natural phenomena that might contribute to erroneous interpretations and measurements. Comparison of yield strengths of Martian and lunar flows with terrestrial flows suggests that the Martian and lunar flows are more akin to terrestrial basalts than they are to terrestrial andesites, trachytes, and rhyolites.

Moore, H. J.↗
NASA NTRS1979

Tensile and flexural strength of non-graphitic superhybrid composites: Predictions and comparisons

Equations are presented and described which can be used to predict bounds on the tensile and flexural strengths of nongraphitic superhybrid (NGSH) composites. These equations are derived by taking into account the measured stress-strain behavior, the lamination residual stresses and the sequence of events leading to fracture. The required input for using these equations includes constituents, properties (elastic and strength), NGSH elastic properties, cure temperature, and ply stress influence coefficients. Results predicted by these equations are in reasonably good agreement with measured data for strength and for the apparent knees in the nonlinear stress-strain curve. The lower bound values are conservative compared to measured data. These equations are relatively simple and are suitable for use in the preliminary design and initial sizing of structural components made from NGSH composites.

Chamis, C. C.↗
NASA NTRS1979

Fracture strength of silicon solar cells

A test program was developed to determine the nature and source of the flaw controlling the fracture of silicon solar cells and to provide information regarding the mechanical strength of cells. Significant changes in fracture strengths were found in seven selected in-process wafer-to-cell products from a manufacturer's production line. The fracture strength data were statistically analyzed and interpreted in light of the exterior flaw distribution of the samples.

Chen, C. P.↗
NASA NTRS1979

Effect of impact damage and holes on the compressive strength of a graphite/epoxy laminate

An experimental investigation has been conducted to determine the effect of low-velocity impact damage and unloaded circular holes on the compressive strength of a 48-ply orthotropic graphite/epoxy flat laminate. Specimens were impacted by a 1.27-cm-diameter aluminum sphere with speeds from 52 to 101 m/x to simulate momenta typical of low-velocity impact hazards that can occur in commercial aircraft service. It is shown that low-velocity impact damage can significantly degrade the static compressive strength of the laminate. Specimens that fail at axial strains above 0.008 in the undamaged condition can fail at strains as low as 0.0031 when impacted at 100 m/s. Circular holes also reduce the static compressive strength of the laminate. The failure strain decreases as the hole diameter increases.

Starnes, J. H., Jr.↗
NASA NTRS1980

Anomalous /C-13/H4:/C-12/H4 line strengths in 2 nu 3

Anomalous intensity ratios between 2 nu 3 singlet lines of C-13 methane and C-12 methane are reported. Absolute strengths of the Q1, R0 and R1 singlets were measured for essentially pure samples of (C-13)H4 and (C-12)H4 at a resolution of 0.035 kaysers at pressures of 10 and 20 Torr, using a computer controlled grating spectrometer. Line strength ratios between the isotopic species are presented which demonstrate a dramatic effect of isotopic substitution on line strengths. If this effect can be observed in the 3 nu 3 vibration-rotation band of methane, which is widely used in planetary atmosphere studies, revision of the (C-12)H4/(C-13)H4 abundance ratios of the outer planets will be necessary.

Fox, K.↗
NASA NTRS1979

Tensile and flexural strength of nongraphitic superhybrid composites - Predictions and comparisons

Equations are presented and described which can be used to predict bounds on the tensile and flexural strengths of nongraphitic superhybrid (NGSH) composites. These equations are derived by taking into account the measured stress-strain behavior, the lamination residual stresses and the sequence of events leading to fracture. The required input for using these equations includes constituent composites, elastic and strength properties, NGSH elastic properties, cure temperature, and ply stress influence coefficients. Results predicted by these equations are in reasonably good agreement with measured data for strength and for the apparent 'knees' in the nonlinear stress-strain curve. The lower bound values are conservative compared to measured data. These equations are relatively simple and should be suitable for use in the preliminary design and initial sizing of structural components made from NGSH composites.

Chamis, C. C.↗
NASA NTRS1981

Strain rate, temperature, and humidity on strength and moduli of a graphite/epoxy composite

Results of an experimental study of the influence of strain rate, temperature and humidity on the mechanical behavior of a graphite/epoxy fiber composite are presented. Three principal strengths (longitudinal, transverse and shear) and four basic moduli (E1, E2, G12 and U12) of a unidirectional graphite/epoxy composite were followed as a function of strain rate, temperature and humidity. Each test was performed at a constant tensile strain rate in an environmental chamber providing simultaneous temperature and humidity control. Prior to testing, specimens were given a moisture preconditioning treatment at 60 C. Values for the matrix dominated moduli and strength were significantly influenced by both environmental and rate parameters, whereas the fiber dominated moduli were not. However, the longitudinal strength was significantly influenced by temperature and moisture content. A qualitative explanation for these observations is presented.

Lifshitz, J. M.↗
NASA NTRS1982

Strength of Rewelded Inconel 718

Inconel 718, nickel-based alloy used extensively for high-temperature structural service, welded repeatedly without detriment to its strength. According to NASA report, tests show 12 repairs on same weld joint do not adversely affect ultimate tensile strenth, yield strength, fatigue strength, metallurgical grain structures, or ability of weld joint to respond to post weld heat treatments.

Bayless, E.↗
NASA NTRS1982

Development of high strength, high temperature ceramics

Improvement in the high-pressure turbopumps, both fuel and oxidizer, in the Space Shuttle main engine were considered. The operation of these pumps is limited by temperature restrictions of the metallic components used in these pumps. Ceramic materials that retain strength at high temperatures and appear to be promising candidates for use as turbine blades and impellers are discussed. These high strength materials are sensitive to many related processing parameters such as impurities, sintering aids, reaction aids, particle size, processing temperature, and post thermal treatment. The specific objectives of the study were to: (1) identify and define the processing parameters that affect the properties of Si3N4 ceramic materials, (2) design and assembly equipment required for processing high strength ceramics, (3) design and assemble test apparatus for evaluating the high temperature properties of Si3N4, and (4) conduct a research program of manufacturing and evaluating Si3N4 materials as applicable to rocket engine applications.

Hall, W. B.↗
NASA NTRS1982

Effects of heating rate on density, microstructure, and strength of Si3N4-6 wt.% Y2O3 and a beta-prime sialon

The effects of the heating rate during sintering/firing on the final density, microstructure, and strength of Si3N4-6 wt% Y2O3 and beta-prime sialon, sintered for four hours at 1750 C, are examined. In Si3N4-6 wt% Y2O3 increasing the heating rate from 7 C/min to 25 C/min to 90 C/min results in a corresponding decrease in the final density from 3.01 g/cu cm to 2.92 g/cu cm to 2.76 g/cu cm. In the beta-prime sialon composition all three heating rates produce an equivalent final density of 3.13 g/cu cm. All heating rates in both compositions produce nonhomogeneous microstructures. The room-temperature strength of Si3N4-6 wt% Y2O3 increases from 372 to 510 MPa with increased density, while the corresponding strengths for the betaprime sialon at equivalent densities are 345 to 445 MPa.

Campbell, S. S.↗
NASA NTRS1982

Line positions and strengths of HDO in the 2400-3300 per cm region

The vibration-rotation spectrum of HDO in the 2400-3300 per cm region has been studied at 0.01 per cm resolution with a Fourier transform spectrometer. Values of the ground state levels and levels in the (100) and (020) states have been determined from the data. The ground state levels are fitted to a Watson-type Hamiltonian from which 17 rotational constants are obtained. Measurements of the strengths of over 1100 lines have been made using a nonlinear least-squares fitting technique, and 548 of these lines are analyzed to determine the band strengths, the coefficients of the F factors, and the Coriolis interaction parameters. The strengths of the A- and B-type (100) bands and the A- and B-type (020) bands are 53.2 + or - 0.9, 0.43 + or - 0.07, 6.00 + or - 0.54, and 2.75 + or - 0.12 per sq cm per atm at 296 K, respectively.

Toth, R. A.↗
NASA NTRS1982

Alumina fiber strength improvement

The effective fiber strength of alumina fibers in an aluminum composite was increased to 173,000 psi. A high temperature heat treatment, combined with a glassy carbon surface coating, was used to prevent degradation and improve fiber tensile strength. Attempts to achieve chemical strengthening of the alumina fiber by chromium oxide and boron oxide coatings proved unsuccessful. A major problem encountered on the program was the low and inconsistent strength of the Dupont Fiber FP used for the investigation.

Pepper, R. T.↗