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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

The use of COD and plastic instability in crack propagation and arrest in shells

The initiation, growth, and possible arrest of fracture in cylindrical shells containing initial defects are dealt with. For those defects which may be approximated by a part-through semi-elliptic surface crack which is sufficiently shallow so that part of the net ligament in the plane of the crack is still elastic, the existing flat plate solution is modified to take into account the shell curvature effect as well as the effect of the thickness and the small scale plastic deformations. The problem of large defects is then considered under the assumptions that the defect may be approximated by a relatively deep meridional part-through surface crack and the net ligament through the shell wall is fully yielded. The results given are based on an 8th order bending theory of shallow shells using a conventional plastic strip model to account for the plastic deformations around the crack border.

Erdogan, F.↗
NASA NTRS1973

Earth Resources Technology Satellite: Non-US standard catalog No. N-13

To provide dissemination of information regarding the availability of Earth Resources Technology Satellite (ERTS) imagery, a Non-U.S. Standard Catalog is published on a monthly schedule. The catalogs identify imagery which has been processed and input to the data files during the preceding month. The Non-U.S. Standard Catalog includes imagery covering all areas except that of the United States, Hawaii, and Alaska. Imagery adjacent to the Continental U.S. and Alaska borders will normally appear in the U.S. Standard Catalog. As a supplement to these catalogs, an inventory of ERTS imagery on 16 millimeter microfilm is available. The catalogs consist of four parts: (1) annotated maps which graphically depict the geographic areas covered by the imagery listed in the current catalog, (2) a computer-generated listing organized by observation identification number (ID) with pertinent information for each image, (3) a computer listing of observations organized by longitude and latitude, and (4) observations which have had changes made in their catalog information since the original entry in the data base.

Source record↗
NASA NTRS1974

Stress intensity factors for deep cracks emanating from the corner formed by a hole intersecting a plate surface

A technique consisting of freezing photo-elasticity and a numerical method was used to obtain stress intensity factors for natural cracks emanating from the corner at which a hole intersects a plate surface. Geometries studied were: (1) crack depth to thickness ratios of approximately 0.2, (2) 0.5 and 0.75; (3) crack depth to crack length ratios of approximately 1.0 to 2.0; and (4) crack length to hole radius ratios of about 0.5 to 2.0. All final crack geometries were grown under monotonic loading and growth was not self similar, with most of the growth occuring through the thickness under remote extension. Stress intensity factors were determined at the intersection of the flaw border.

Mcgowan, J. J.↗
NASA NTRS1974

Mixed mode stress intensity factors for semielliptical surface cracks

The three-dimensional equations of elasticity are solved for a flat elliptical crack which has nonuniform shear stresses applied to its surfaces. An alternating method is used to determine the mode two and mode three stress intensity factors for a semielliptical surface crack in the surface of a finite thickness solid. These stress intensity factors are presented as a function of position along the crack border for a number of crack shapes and crack depths. This same technique is followed to determine the mode one stress intensity factors for the semielliptical surface crack which has normal loading applied to its surface. Mode one stress intensity factors are presented and compared with the results obtained from previous work.

Smith, F. W.↗
NASA NTRS1975

Technique and computer program for calculating photographic film density variations

Film density data that have been digitalized and recorded in binary coded decimal (BCD) format are converted into a number representing the film density difference between the unexposed film border and any point on a photograph by program CONVERT. The difference AVERAGE, the BCD number representing the unexposed film area and the BCD number of a specific data point is calculated and then multiplied by three constants to produce the desired film density difference. The angle off the principal axis of the lens is computed for each data point in order that a correction factor be applied to compensate for atmospheric backscattering differences and light intensity fall-off, inherent in the camera lens system in use. The program is capable of plotting the calculated density differences. The percentage of points in specific density ranges can also be computed.

Ohlhorst, C. W.↗
NASA NTRS1974

Penny-shaped crack in a fiber-reinforced matrix

Using a slender inclusion model developed earlier, the elastostatic interaction problem between a penny-shaped crack and elastic fibers in an elastic matrix is formulated. For a single set and for multiple sets of fibers oriented perpendicularly to the plane of the crack and distributed symmetrically on concentric circles, the problem was reduced to a system of singular integral equations. Techniques for the regularization and for the numerical solution of the system are outlined. For various fiber geometries numerical examples are given, and distribution of the stress intensity factor along the crack border was obtained. Sample results showing the distribution of the fiber stress and a measure of the fiber-matrix interface shear are also included.

Narayanan, T. V.↗
NASA NTRS1975

LANDSAT: Non-US standard catalog no. N-33

A catalog used for dissemination of information regarding the availability of LANDSAT imagery is presented. The Image Processing Facility of the Goddard Space Flight Center, publishes a U.S. and a Non-U.S. Standard Catalog on a monthly schedule, and the catalogs identify imagery which has been processed and input to the data files during the referenced month. The U.S. Standard Catalog includes imagery covering the continental United States, Alaska and Hawaii; the Non-U.S. Catalog identifies all the remaining coverage. Imagery adjacent to the continental U.S. and Alaska borders is included in the U.S. Standard Catalog.

Source record↗
NASA NTRS1975

Remote sensing over North Merritt Island

The author has identified the following significant results. For monitoring the surface environment of North Merritt Island, two methods are studied, namely, color infrared photography and machine processing of LANDSAT multispectral scanner data. C.I.R. photos made at a height of about 12,000 ft were found to define the borders of ground features around the space shuttle runway with a nonsignificant mean error of 0.138 meters but a wide range, which can be reduced with photos taken at about 6,000 ft. LANDSAT multispectral scanner data, transformed by use of the function f(g) = g1 + g2 -g3 -g4 where g1, g2, g3, and g4 represent reflectance or grey levels of multispectral channels 1,2,3, and 4, gave values which are classifiable into a relatively small number of categories.

Poonai, P.↗
NASA NTRS1974

Anthropogenic desertification by high-albedo pollution Observations and modeling

ERTS-1 MSS albedo data of Western Negev, Sinai and the Gaza strip are presented. A sharp contrast in albedo exists across the Negev-Sinai and Negev-Gaza strip borders. Anthropogenic desertification has occurred on the Arab side due to overgrazing and Bedouin agriculture, whereas natural vegetation grows much more abundantly on the Israeli side.

Otterman, J.↗
NASA NTRS1975

Radar for small-scale land-use mapping

Small-scale (1:250,000 and smaller) land-use maps are a major concern not only to geographers but also to national and regional planners. Unfortunately, such maps are usually out of date by the time they are printed. An interpretation key consisting of five physical and cultural characteristics of the environment evident on radar imagery is used to create land-use regions. Regions and borders interpreted from radar are compared with those found on two existing land-use maps created by traditional methods. Radar imagery can be used to create a small-scale land-use map with regions comparable to those found on existing land-use maps. However, the radar regions depict something more than land use and should be termed rural landscape regions.

Henderson, F. M.↗
NASA NTRS1974

Orange glass - Evidence for regional deposits of pyroclastic origin on the moon

Crystallized spheres of orange glass from Shorty Crater at the Apollo 17 site are shown by spectral reflectance data to be the characteristic ingredient of the dark mantling deposit of the Taurus-Littrow region. This deposit, mapped on spectral vidicon images taken using earth-based telescopes, apparently is thickest 50 km northwest of the Apollo 17 landing area, and has a gradational contact with the surrounding materials. The irregular areal distribution of the dark-mantle deposit and the gradational borders support conclusions based on laboratory studies of the orange soils that these are volcanic pyroclastic materials. Similar deposits are identified by spectral reflectance properties near Rima Bode, Schroeter W, Fauth H, and Higinus W. The same material is likely to occur at Sulpucius Gallus based on visual and photographic observations of orange soil. The apparently restricted occurrence of the orange-glass deposits in a belt along the edges of major mare basins implies structural control of volcanic vents and a possible deep-seated origin.

Adams, J. B.↗
NASA NTRS1975

Variable features on Mars V - Evidence for crater streaks produced by wind erosion

High-resolution television pictures obtained by Mariner 9 are presented as evidence to show that the ragged dark streaks which appeared behind many dark craters several months after the end of the 1971 global dust storm resulted from wind erosion of a thin surface veneer consisting of dust-storm fallout. The pictures were taken over an area near the border between Mare Serpentis and Pandorae Fretum (approximately 30 deg S, 335 deg W). The high-resolution pictures are compared with low-resolution views of the same area, and it is shown that one very long dark streak is interrupted by a rille. It is concluded that this interruption proves that the dark streaks were produced by the present erosional mechanism.

Veverka, J.↗
NASA NTRS1975

On fracture toughness in the nonlinear range

A general definition of fracture toughness is developed which is appropriate to situations of subcritical crack growth and/or large-scale crack border plastic yield. The theoretical basis as well as comparisons with other proposed measures of fracture toughness are discussed. A simple method is given for evaluating fracture toughness which is based on use of the load-displacement test record.

Eftis, J.↗
NASA NTRS1975

A study of the early detection of insect infestations and density/distribution of host plants

The author has identified the following significant results. With comparative observations of film types and seasonal influences on reflectance characteristics, many crop varieties can be identified. This study shows that citrus, sugar cane, brush, some winter vegetables, and grain crops could be identified. Vegetative patterns in border areas can be detected. This information can be useful in detecting avenues of entry of pest species and areas of stress that require vigilance in stopping the spread of destructive species. Influence of some environmental factors on crops that may be confused with pest injury, or related factors, can be detected and identified with Skylab data (S-190B).

Hart, W. G.↗
NASA NTRS1975

Skylab photography applied to geologic mapping in northwestern Central America

Two photolineation maps of southwestern Guatemala and Chiapas were made from S190 photographs along a ground track from Acajutla, El Salvador to San Cristobal de las Casas, Mexico. The maps document a structural complexity spanning the presumed triple junction of the Cocos, Americas, and Caribbean plates. The Polochic fault zone, supposedly the Americas-Caribbean plate boundary, is a sharply delineated feature across western Guatemala. Westward of the Mexican border it splays into a large number of faults with NW to SW trends. The structural pattern is quite different to the north (Americas plate) and to the south (Caribbean plate) of the Polochic fault, though both areas are dominated by NW-trending lineations. Within the Central American volcanic chain, the lineation patterns support the segmented model of the Benioff Zone, by showing a concentration of transverse lineations in the predicted locations, most notably NE-trending elements near Quezaltenango, Guatemala. The structural pattern obtained from the maps are compared to patterns described on recently published maps of more southerly parts of Central America, to begin a synthesis of the structure of the convergent plate boundary.

Rose, W. I., Jr.↗
NASA NTRS1976

Application of Skylab EREP data for land use management

The author has identified the following significant results. The 1.09-1.19 micron band proved to be very valuable for discriminating a variety of land use categories, including agriculture, forest, and urban classes. The 1.55-1.75 micron band proved very useful in combination with the 1.09-1.19 micron band. Misregistration between spectral bands, even by as little as 1/2 pixel, may degrade classification accuracy. Identification accuracy of boundary or border pixels was as much as 13% lower than the accuracy for identifying internal field pixels. The principal conclusion with respect to the S190B camera system is that the higher resolution of the S190B system in comparison to previous space photography (Gemini, Apollo), to the S190A system (Skylab), and to LANDSAT imagery significantly increases the range of additional discrimination achievable.

Simonett, D. S.↗
NASA NTRS1976

Application of satellite data and LARS's data processing techniques to mapping vegetation of the Dismal Swamp

The feasibility of using digital satellite imagery and automatic data processing techniques as a means of mapping swamp forest vegetation was considered, using multispectral scanner data acquired by the LANDSAT-1 satellite. The site for this investigation was the Dismal Swamp, a 210,000 acre swamp forest located south of Suffolk, Va. on the Virginia-North Carolina border. Two basic classification strategies were employed. The initial classification utilized unsupervised techniques which produced a map of the swamp indicating the distribution of thirteen forest spectral classes. These classes were later combined into three informational categories: Atlantic white cedar (Chamaecyparis thyoides), Loblolly pine (Pinus taeda), and deciduous forest. The subsequent classification employed supervised techniques which mapped Atlantic white cedar, Loblolly pine, deciduous forest, water and agriculture within the study site. A classification accuracy of 82.5% was produced by unsupervised techniques compared with 89% accuracy using supervised techniques.

Messmore, J. A.↗