7,107 research outputs found
Closed form expressions for crack mouth displacements and stress intensity factors for chevron notched short bar and short rod specimens based on experimental compliance measurements
A set of equations are presented describing certain fracture mechanics parameters for chevron notch bar and rod specimens. They are developed by fitting compliance calibration data reported earlier. The equations present the various parameters in their most useful forms. The data encompass the entire range of the specimen geometries most commonly used. Their use will facilitate the testing and analysis of brittle metals, ceramics, and glasses
Fracture toughness of brittle materials determined with chevron notch specimens
The use of chevron-notch specimens for determining the plane strain fracture toughness (K sub Ic) of brittle materials is discussed. Three chevron-notch specimens were investigated: short bar, short rod, and four-point-bend. The dimensionless stress intensity coefficient used in computing K sub Ic is derived for the short bar specimen from the superposition of ligament-dependent and ligament-independent solutions for the straight through crack, and also from experimental compliance calibrations. Coefficients for the four-point-bend specimen were developed by the same superposition procedure, and with additional refinement using the slice model of Bluhm. Short rod specimen stress intensity coefficients were determined only by experimental compliance calibration. Performance of the three chevron-notch specimens and their stress intensity factor relations were evaluated by tests on hot-pressed silicon nitride and sintered aluminum oxide. Results obtained with the short bar and the four-point-bend specimens on silicon nitride are in good agreement and relatively free of specimen geometry and size effects within the range investigated. Results on aluminum oxide were affected by specimen size and chevron-notch geometry, believed due to a rising crack growth resistance curve for the material. Only the results for the short bar specimen are presented in detail
Highlights of unsteady pressure tests on a 14 percent supercritical airfoil at high Reynolds number, transonic condition
Steady and unsteady pressures were measured on a 2-D supercritical airfoil in the Langley Research Center 0.3-m Transonic Cryogenic Tunnel at Reynolds numbers from 6 x 1,000,000 to 35 x 1,000,000. The airfoil was oscillated in pitch at amplitudes from plus or minus .25 degrees to plus or minus 1.0 degrees at frequencies from 5 Hz to 60 Hz. The special requirements of testing an unsteady pressure model in a pressurized cryogenic tunnel are discussed. Selected steady measured data are presented and are compared with GRUMFOIL calculations at Reynolds number of 6 x 1,000,000 and 30 x 1,000,000. Experimental unsteady results at Reynolds numbers of 6 x 1,000,000 and 30 x 1,000,000 are examined for Reynolds number effects. Measured unsteady results at two mean angles of attack at a Reynolds number of 30 x 1,000,000 are also examined
Analysis of some compliance calibration data for chevron-notch bar and rod specimens
A set of equations describing certain fracture mechanics parameters for chevron-notch bar and rod specimens are presented. They are developed by fitting earlier compliance calibration data. The difficulty in determining the minimum stress intensity coefficient and the critical crack length is discussed
The influence of composition, annealing treatment, and texture on the fracture toughness of Ti-5Al-2.5Sn plate at cryogenic temperatures
The plane strain fracture toughness K sub Ic and conventional tensile properties of two commercially produced one-inch thick Ti-5Al-2.5Sn plates were determined at cryogenic temperatures. One plate was extra-low interstitial (ELI) grade, the other normal interstitial. Portions of each plate were mill annealed at 1088 K (1500 F) followed by either air cooling or furnace cooling. The tensile properties, flow curves, and K sub Ic of these plates were determined at 295 K (room temperature), 77 K (liquid nitrogen temperature), and 20 K (liquid hydrogen temperature)
Flux calibration of the AAO/UKST SuperCOSMOS H-alpha Survey
The AAO/UKST SuperCOSMOS H Survey (SHS) was, when completed in 2003,
a powerful addition to extant wide-field surveys. The combination of areal
coverage, spatial resolution and sensitivity in a narrow imaging band, still
marks it out today as an excellent resource for the astronomical community. The
233 separate fields are available online in digital form, with each field
covering 25 square degrees. The SHS has been the motivation for equivalent
surveys in the north, and new digital H surveys now beginning in the
south such as VPHAS+. It has been the foundation of many important discovery
projects with the Macquarie/AAO/Strasbourg H planetary nebula project
being a particularly successful example. However, the full potential of the SHS
has been hampered by lack of a clear route to acceptable flux calibration from
the base photographic data. We have determined the calibration factors for 170
individual SHS fields, and present a direct pathway to the measurement of
integrated H fluxes and surface brightnesses for resolved nebulae
detected in the SHS. We also include a catalogue of integrated H fluxes
for 100 planetary and other nebulae measured from the SHS, and use these
data to show that fluxes, accurate to 0.10 - 0.14 dex (25-35 per
cent), can be obtained from these fields. For the remaining 63 fields, a mean
calibration factor of 12.0 counts pix R can be used, allowing the
determination of reasonable integrated fluxes accurate to better than 0.2
dex (50 per cent). We outline the procedures involved and the caveats
that need to be appreciated in achieving such flux measurements. This paper
forms a handy reference source that will significantly increase the scientific
utility of the SHS.Comment: 14 pages, 12 figures, 2 tables (plus 7 pp. of supplementary online
information). Version to appear in MNRA
Future humidity trends over the western United States in the CMIP5 global climate models and variable infiltration capacity hydrological modeling system
Global climate models predict relative humidity (RH) in the western US will decrease at a rate of about 0.1–0.6 percentage points per decade, albeit with seasonal differences (most drying in spring and summer), geographical variability (greater declines in the interior), stronger reductions for greater anthropogenic radiative forcing, and notable spread among the models. Although atmospheric moisture content increases, this is more than compensated for by higher air temperatures, leading to declining RH. Fine-scale hydrological simulations driven by the global model results should reproduce these trends. It is shown that the MT-CLIM meteorological algorithms used by the Variable Infiltration Capacity (VIC) hydrological model, when driven by daily Tmin, Tmax, and precipitation (a configuration used in numerous published studies), do not preserve the original global model\u27s humidity trends. Trends are biased positive in the interior western US, so that strong RH decreases are changed to weak decreases, and weak decreases are changed to increases. This happens because the MT-CLIM algorithms VIC incorporates infer an overly large positive trend in atmospheric moisture content in this region, likely due to an underestimate of the effect of increasing aridity on RH. The result could downplay the effects of decreasing RH on plants and wildfire. RH trends along the coast have a weak negative bias due to neglect of the ocean\u27s moderating influence. A numerical experiment where the values of Tdew are altered to compensate for the RH error suggests that eliminating the atmospheric moisture bias could, in and of itself, decrease runoff up to 14% in high-altitude regions east of the Sierra Nevada and Cascades, and reduce estimated Colorado River runoff at Lees Ferry up to 4% by the end of the century. It could also increase the probability of large fires in the northern and central US Rocky Mountains by 13 to 60%
Sun-as-a-Star Spectrum Variations 1974-2006
We have observed selected Fraunhofer lines, both integrated over the Full
Disk and for a small circular region near the center of the solar disk, on
1,215 days for the past 30 years. Full Disk results: Ca II K 393 nm nicely
tracks the 11 year magnetic cycle based on sunspot number with a peak amplitude
in central intensity of ~37%. The wavelength of the mid-line core absorption
feature, called K3, referenced to nearby photospheric Fe, displays an activity
cycle variation with an amplitude of 3 milli-Angstroms. Other chromospheric
lines track Ca II K intensity with lower relative amplitudes. Low photosphere:
Temperature sensitive CI 5380 nm appears constant in intensity to 0.2%. High
photosphere: The cores of strong Fe I lines, Na D1 and D2, and the Mg I b
lines, present a puzzling signal perhaps indicating a role for the 22 y Hale
cycle. Solar minimum around 1985 was clearly seen, but the following minimum in
1996 was missing. This anomalous behavior is not seen in comparison atmospheric
O2. Center Disk results: Both Ca II K and C I 538 nm intensities are constant,
indicating that the basal quiet atmosphere is unaffected by cycle magnetism
within our observational error. A lower limit to the Ca II K central intensity
atmosphere is 0.040. The wavelength of Ca II K3 varies with the cycle by 6
milli-Angstroms, a factor of 2X over the full disk value. This may indicate the
predominance of radial motions at Center Disk. This is not an effect of motions
in plages since they are absent at Center Disk. This 11 y variation in the
center of chromospheric lines could complicate the radial velocity detection of
planets around solar-type stars. An appendix provides instructions for URL
access to both the raw and reduced data.Comment: 38 pages with 20 figures. Accepted for publication in The
Astrophysical Journa
Improved to Transformation Equations for Main Sequence Stars
We report improved transformation equations between the and
photometric systems. Although the details of the transformations
depend on luminosity class, we find a typical rms scatter on the order of 0.001
magnitude if the sample is limited to main sequence stars. Furthermore, we find
an accurate transformation requires complex, multi-color dependencies for the
bluer bandpasses. Results for giant stars will be reported in a subsequent
paper.Comment: 7 pages, 8 figure
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