An evaluation of the pressure proof test concept for thin sheet 2024-T3

The concept of pressure proof testing of fuselage structures with fatigue cracks to insure structural integrity was evaluated from a fracture mechanics viewpoint. A generic analytical and experimental investigation was conducted on uniaxially loaded flat panels with crack configurations and stress levels typical of longitudinal lap splice joints in commercial transport aircraft fuselages. The results revealed that the remaining fatigue life after a proof test was longer than that without the proof test because of crack growth retardation due to increased crack closure. However, based on a crack length that is slightly less than the critical value at the maximum proof test stress, the minimum assured life or proof test interval must be no more than 550 pressure cycles for a 1.33 proof factor and 1530 pressure cycles for a 1.5 proof factor to prevent in-flight failures

Error analysis and corrections to pupil diameter measurements with Langley Research Center's oculometer

Factors that can affect oculometer measurements of pupil diameter are: horizontal (azimuth) and vertical (elevation) viewing angle of the pilot; refraction of the eye and cornea; changes in distance of eye to camera; illumination intensity of light on the eye; and counting sensitivity of scan lines used to measure diameter, and output voltage. To estimate the accuracy of the measurements, an artificial eye was designed and a series of runs performed with the oculometer system. When refraction effects are included, results show that pupil diameter is a parabolic function of the azimuth angle similar to the cosine function predicted by theory: this error can be accounted for by using a correction equation, reducing the error from 6% to 1.5% of the actual diameter. Elevation angle and illumination effects were found to be negligible. The effects of counting sensitivity and output voltage can be calculated directly from system documentation. The overall accuracy of the unmodified system is about 6%. After correcting for the azimuth angle errors, the overall accuracy is approximately 2%

Surface crack analysis applied to impact damage in a thick graphite-epoxy composite

The residual tensile strength of a thick graphite/epoxy composite with impact damage was predicted using surface crack analysis. The damage was localized to a region directly beneath the impact site and extended only part way through the laminate. The damaged region contained broken fibers, and the locus of breaks in each layer resembled a crack perpendicular to the direction of the fibers. In some cases, the impacts broke fibers without making a visible crater. The impact damage was represented as a semi-elliptical surface crack with length and depth equal to that of the impact damage. The maximum length and depth of the damage were predicted with a stress analysis and a maximum shear stress criterion. The predictions and measurements of strength were in good agreement

Mechanical properties of several nickel alloys in hydrogen at elevated temperatures

Tests were performed to determine low cycle fatigue and crack growth rate properties of one iron-base and two forms of one cast nickel-base alloy. The alloys were tested in various forms and/or heat-treat conditions that are proposed for use in a high-pressure hydrogen or a hydrogen-water vapor environment. Some general conclusions can be made comparing the results of tests in a hydrogen environment with those in a hydrogen-water vapor environment. The hydrogen-water vapor environment caused a 50 percent average reduction in fatigue life, indicating extreme degradation when compared with tests conducted in air, for Incoloy 903 at 1033 K (1400 F). Crack growth rates increased significantly for all materials with increasing test temperature. A very significant increase (three orders of magnitude) in crack growth rate occurred for Incoloy 903 tested in the hydrogen-water vapor environment when compared with testing done in hydrogen along at 922 K (1200 F)

The Global Competitiveness of the North American Livestock Industry

Livestock Production/Industries, F14, Q17,

Atmospheric particulate measurements in Norfolk, Virginia

Characterization of atmospheric particulates was conducted at a site near the center of Norfolk, Virginia. Air quality was measured in terms of atmospheric mass loading, particle size distribution, and particulate elemental composition for a period of 2 weeks. The objectives of this study were (1) to establish a mean level of air quality and deviations about this mean, (2) to ascertain diurnal changes or special events in air quality, and (3) to evaluate instrumentation and sampling schedules. Simultaneous measurements were made with the following instruments: a quartz crystal microbalance particulate monitor, a light-scattering multirange particle counter, a high-volume air sampler, and polycarbonate membrane filters. To assess the impact of meteorological conditions on air quality variations, continuous data on temperature, relative humidity, wind speed, and wind direction were recorded. Particulate elemental composition was obtained from neutron activation and scanning electron microscopy analyses of polycarbonate membrane filter samples. The measured average mass loading agrees reasonably well with the mass loadings determined by the Virginia State Air Pollution Control Board. There are consistent diurnal increases in atmospheric mass loading in the early morning and a sample time resolution of 1/2 hour seems necessary to detect most of the significant events

Effluent sampling of Scout D and Delta launch vehicle exhausts

Characterization of engine-exhaust effluents (hydrogen chloride, aluminum oxide, carbon dioxide, and carbon monoxide) has been attempted by conducting field experiments monitoring the exhaust cloud from a Scout-Algol III vehicle launch and a Delta-Thor vehicle launch. The exhaust cloud particulate size number distribution (total number of particles as a function of particle diameter), mass loading, morphology, and elemental composition have been determined within limitations. The gaseous species in the exhaust cloud have been identified. In addition to the ground-based measurements, instrumented aircraft flights through the low-altitude, stabilized-exhaust cloud provided measurements which identified CO and HCI gases and Al2O3 particles. Measurements of the initial exhaust cloud during formation and downwind at several distances have established sampling techniques which will be used for experimental verification of model predictions of effluent dispersion and fallout from exhaust clouds

New species of microcaddisfl ies (Trichoptera: Hydroptilidae) from the western United States, Canada, Mexico and Belize

Nine new species of Hydroptilidae (Trichoptera) are described and illustrated from the western United States, Canada, Mexico, and Belize: Seven new species in the genus Neotrichia Morton, N. buenoi, N. chihuaha, N. contrerasi, N. maya, N. palitla, N. pinnacles, and N. sandersoni, one new species in the genus Oxyethira Eaton, O. pembertonensis, and one new species in the genus Metrichia Ross, M. mastelleri. As well, new records for N. mobilensis and Mayatrichia tuscaloosa and new illustrations of the male genitalia of Neotrichia jarochita Bueno- Soria and Mayatrichia tuscaloosa Harris and Sykora are provided