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At least 145 records · Page 8

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NASA NTRS1957

Rupture Strength of Several Nickel-base Alloys in Sheet Form

The 100-hour rupture strengths of Inconel X, Inconel 700, Incoloy 901, Refractaloy 26, and R-235 at 1200 and 1350 F. in both the annealed and heat-treated conditions were determined. Inconel 700 had the highest rupture strength at both temperatures; Incoloy 901 was second strongest at 1200 F, and R-235 second strongest at 1350 F. With the exception of Incoloy 901, ductility was low. Photomicrographs show that fractures are through the grain boundaries. Results are compared with published data for other sheet alloys and bar stock.

ALLOYS, HEAT-RESISTING↗

NASA NTRS1957

Effect of plastic viscosity and yield value on spray characteristics of magnesium-slurry fuel

Magnesium slurries were sprayed onto a sheet of paper from an air-atomizing injector. Drop sizes and distributions were then determined from photomicrographs. Four different surface-active additives were used in preparing the slurries to give plastic viscosities between 0.22 and 0.51 poise and yield values between 150 and 810 dynes-cm(exp 2). It was found that there was no significant variation in the spray characteristics of these slurries when tested under the same conditions.

Prok, George M↗

NASA NTRS1940

Mechanical Properties of Flush-Riveted Joints

The strength of representative types of flush-riveted joints has been determined by testing 865 single-shearing, double-shearing, and tensile specimens representing 7 types of rivet and 18 types of joint. The results, presented in graphic form, show the stress at failure, type of failure, and d/t ratio. In general, dimpled joints were appreciably stronger than countersunk or protruding-head joints, but their strength was greatly influenced by constructional details. The optimum d/t ratios have been determined for the several kinds of joints. Photomicrographs of each type show constructional details and, in several instances, cracks in the sheet.

Brueggeman, W C↗

NASA NTRS1951

Investigation of Fretting by Microscopic Observation

An experimental investigation, using microscopic observation and color motion photomicrographs of the action, was conducted to determine the cause of fretting. Glass and other noncorrosive materials, as well as metals, were used as specimens. A very simple apparatus vibrated convex surfaces in contact with stationary flat surfaces at frequencies of 120 cycles or less than l cycle per second, an amplitude of 0.0001 inch, and load of 0.2 pound.

Godfrey, Douglas↗

NASA NTRS1993

Surface characterization of LDEF materials

The NASA Long Duration Exposure Facility (LDEF), a passive experimental satellite, was placed into low-Earth orbit by the Shuttle Challenger in Apr. 1984. The LDEF spent an unprecedented 69 months in space. The flight and recovery of the LDEF provided a wealth of information on the longterm space environmental effects of a variety of materials exposed to the low-Earth orbit environment. Surface characterization of LDEF materials included polymers, composites, thermal control paints, and aluminum. X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), scanning electron microscopy (SEM), and contact angle analysis were used to document changes in both the surface composition and surface chemistry of these materials. Detailed XPS analysis of the polymer systems, such as Kapton, polyimide polysiloxane copolymers, and fluorinated ethylene propylene thermal blankets on the backside of the LDEF revealed significant changes in both the surface composition and surface chemistry as a result of exposure to the low-Earth orbit environment. Polymer systems such as Kapton, polyimide polysiloxane copolymers, and polysulfone showed a common trend of decreasing carbon content and increasing oxygen content with respect to the control sample. Carbon 1s curve fit XPS analysis of the composite samples, in conjunction with SEM photomicrographs, revealed significant ablation of the polymer matrix resin to expose the carbon fibers of the composite during exposure to the space environment. Surface characterization of anodized aluminum tray clamps, which were located at regular intervals over the entire LDEF frame, provided the first results to evaluate the extent of contamination with respect to position on the LDEF. The XPS results clearly showed that the amount and state of both silicon and fluorine contamination were directly dependent upon the position of the tray clamp on the LDEF.

Wightman, J. P.↗

NASA NTRS1993

Insoluble coatings for Stirling engine heat pipe condenser surfaces

The work done by Thermacore, Inc., Lancaster, Pennsylvania, for the Phase 1, 1992 SBIR National Aeronautics and Space Administration Contract, 'Insoluble Coatings for Stirling Engine Heat Pipe Condenser Surfaces' is described. The work was performed between January 1992 and July 1992. Stirling heat engines are being developed for electrical power generation use on manned and unmanned earth orbital and planetary missions. Dish Stirling solar systems and nuclear reactor Stirling systems are two of the most promising applications of the Stirling engine electrical power generation technology. The sources of thermal energy used to drive the Stirling engine typically are non-uniform in temperature and heat flux. Liquid metal heat pipe receivers are used as thermal transformers and isothermalizers to deliver the thermal energy at a uniform high temperature to the heat input section of the Stirling engine. The use of a heat pipe receiver greatly enhances system efficiency and potential life span. One issue that is raised during the design phase of heat pipe receivers is the potential solubility corrosion of the Stirling engine heat input section by the liquid metal working fluid. This Phase 1 effort initiated a program to evaluate and demonstrate coatings, applied to nickel based Stirling engine heater head materials, that are practically 'insoluble' in sodium, potassium, and NaK. This program initiated a study of nickel aluminide as a coating and developed and demonstrated a heat pipe test vehicle that can be used to test candidate materials and coatings. Nickel 200 and nickel aluminide coated Nickel 200 were tested for 1000 hours at 800 C at a condensation heat flux of 25 W/sq cm. Subsequent analyses of the samples showed no visible sign of solubility corrosion of either coated or uncoated samples. The analysis technique, photomicrographs at 200X, has a resolution of better than 2.5 microns (.0001 in). The results indicate that the heat pipe environment is not directly comparable to liquid metal pumped loop data, that nickel aluminide is still a leading candidate for solubility corrosion protection, and that longer duration tests are required to reach a definitive conclusion whether coatings are required at all. Should further testing be required, the test vehicle and analytical tools were developed.

Dussinger, Peter M.↗

NASA NTRS1993

Grain surface features of Apollo 17 orange and black glass

Lunar soil sample 74220 and core samples 74001/2 consist mainly of orange glass droplets, droplet fragments, and their crystallized equivalents. These samples are now generally accepted to be pyroclastic ejecta from early lunar volcanic eruptions. It has been known that they contain surface coatings and material rich in volatile condensable phases including S, Zn, F, Cl, and many volatile metals. Meyer summarizes the voluminous published chemical data and calculates the volatile enrichment ratios for most of the surface condensates. In an attempt to more completely understand this enrichment of surface volatiles, we have searched for carbon and carbon-bearing phases on droplet surfaces. We have reviewed many of our existing photomicrographs and energy dispersive analysis (EDX) of grain surfaces and have reexamined some of our older SEM mounts using an improved EDXA system capable of light element detection and analysis (oxygen, nitrogen, and carbon). In addition, we have made fresh mounts using procedures which should minimize carbon contamination or extraneous carbon x-rays and have analyzed for carbon.

Mckay, David S.↗

NASA NTRS1995

Surface characterization of LDEF carbon fiber/polymer matrix composites

XPS (x-ray photoelectron spectroscopy) and SEM (scanning electron microscopy) analysis of both carbon fiber/epoxy matrix and carbon fiber/polysulfone matrix composites revealed significant changes in the surface composition as a result of exposure to low-earth orbit. The carbon 1s curve fit XPS analysis in conjunction with the SEM photomicrographs revealed significant erosion of the polymer matrix resins by atomic oxygen to expose the carbon fibers of the composite samples. This erosion effect on the composites was seen after 10 months in orbit and was even more obvious after 69 months.

Grammer, Holly L.↗

NASA NTRS1992

Mechanical properties of triaxially braided composites: Experimental and analytical results

The unnotched tensile properties of 2-D triaxial braid reinforced composites from both an experimental and an analytical viewpoint are studied. The materials are graphite fibers in an epoxy matrix. Three different reinforcing fiber architectures were considered. Specimens were cut from resin transfer molded (RTM) composite panels made from each braid. There were considerable differences in the observed elastic constants from different size strain gage and extensometer reading. Larger strain gages gave more consistent results and correlated better with the extensometer reading. Experimental strains correlated reasonably well with analytical predictions in the longitudinal, 0 degrees, fiber direction but not in the transverse direction. Tensile strength results were not always predictable even in reinforcing directions. Minor changes in braid geometry led to disproportionate strength variations. The unit cell structure of the triaxial braid was discussed with the assistance of computer analysis of the microgeometry. Photomicrographs of braid geometry were used to improve upon the computer graphics representations of unit cells. These unit cells were used to predict the elastic moduli with various degrees of sophistication. The simple and the complex analyses were generally in agreement but none adequately matched the experimental results for all the braids.

Masters, John E.↗

NASA NTRS1993

Effects of temperature and humidity cycling on the strengths of textile reinforced carbon/epoxy composite materials

Results are presented from an experimental evaluation of the combined effects of temperature and humidity cycling on AS4/3501-6 composites (unstitched, Kevlar 29 stitched, and S-2 glass stitched uniweave fabric) and AS4/E905L composites (2-D, S-2 glass stitched 2-D, and 3-D braided fabric). The AS4/3501-6 uniweave material had a quasi-isotropic layup, whereas the AS4/E905L materials were braided in a (+/-30 deg/0 deg)(sub s) orientation. Data presented include compression strengths and compression-compression fatigue results for uncycled composites and cycled composites (160, 480, 720, and 1280 cycles from 140 deg F at 95 percent relative humidity to -67 deg F). To observe the presence of microcracking within the laminates, photomicrographs were taken of each material type at the end of each cycling period. Microcracks were found to be more prevalent within stitched laminates, predominantly around individual stitches. The glass stitched laminates showed significant microcracking even before cycling. Less microcracking was evident in the Kevlar stitched materials, whereas the unstitched uniweave material developed microcracks only after cycling. The 3-D braid did not develop microcracks. The static compression strengths of the unstitched and Kevlar stitched uniweave materials were degraded by about 10 percent after 1280 temperature/humidity cycles, whereas the reduction in compression strength for the glass stitched uniweave was less than 3 percent. The reduction in compression strength for the glass stitched 2-D braid was less than 8 percent. The unstitched 2-D and 3-D braids did not lose strength from temperature/humidity cycling. The compression-compression fatigue properties of all six material types were not affected by temperature/humidity cycling.

Cano, Roberto J.↗

NASA NTRS1997

[Effects of Gravity on Attachment of Tendon to Bone]

We have received and processed all samples for either light or scanning electron microscopic analysis and have completed the histomorphometric analysis. We have characterized the changes caused by spaceflight to tendon attachments to the calcaneus, tibia, fibula and femur and compared them to hindlimbs and forelimbs from NIH.RZ. Soleus muscle histomorphometry has also been completed. Our results suggest severe osteoporosis in the femur, fibula and tibia of animals coincident to spaceflight, which had not resolved after 4-5 days following return to earth. This was evident at all sites, including sites of tendon attachments. This atrophy was not evident in the calcaneus. No muscle atrophy was evident. Comparison of scanning photomicrographs of flight animals with other lactating animals demonstrated structural similarities and suggested that it might be worthwhile to assess whether lactation is a factor in development of the osteoporosis in the spaceflight animals. In addition, evaluation of total calcium utilization by spaceflight animals would be beneficial.

Johnson, Roger B.↗

NASA NTRS1998

Mineralization of Bacteria in Terrestrial Basaltic Rocks: Comparison With Possible Biogenic Features in Martian Meteorite Allan Hills 84001

The identification of biogenic features altered by diagenesis or mineralization is important in determining whether specific features in terrestrial rocks and in meteorites may have a biogenic origin. Unfortunately, few studies have addressed the formation of biogenic features in igneous rocks, which may be important to these phenomena, including the controversy over possible biogenic features in basaltic martian meteorite ALH84001. To explore the presence of biogenic features in igneous rocks, we examined microcosms growing in basaltic small-scale experimental growth chambers or microcosms. Microbial communities were harvested from aquifers of the Columbia River Basalt (CRB) group and grown in a microcosm containing unweathered basalt chips and groundwater (technique described in. These microcosms simulated natural growth conditions in the deep subsurface of the CRB, which should be a good terrestrial analog for any putative martian subsurface ecosystem that may have once included ALH84001. Here we present new size measurements and photomicrographs comparing the putative martian fossils to biogenic material in the CRB microcosms. The range of size and shapes of the biogenic features on the CRB microcosm chips overlaps with and is similar to those on ALH84001 chips. Although this present work does not provide evidence for the biogenicity of ALH84001 features, we believe that, based on criteria of size, shape, and general morphology, a biogenic interpretation for the ALH84001 features remains plausible.

Thomas-Keprta, K. L.↗

NASA NTRS1998

A New Image Processing and GIS Package

The image processing and GIS package ELAS was developed during the 1980's by NASA. It proved to be a popular, influential and powerful in the manipulation of digital imagery. Before the advent of PC's it was used by hundreds of institutions, mostly schools. It is the unquestioned, direct progenitor or two commercial GIS remote sensing packages, ERDAS and MapX and influenced others, such as PCI. Its power was demonstrated by its use for work far beyond its original purpose, having worked several different types of medical imagery, photomicrographs of rock, images of turtle flippers and numerous other esoteric imagery. Although development largely stopped in the early 1990's the package still offers as much or more power and flexibility than any other roughly comparable package, public or commercial. It is a huge body or code, representing more than a decade of work by full time, professional programmers. The current versions all have several deficiencies compared to current software standards and usage, notably its strictly command line interface. In order to support their research needs the authors are in the process of fundamentally changing ELAS, and in the process greatly increasing its power, utility, and ease of use. The new software is called ELAS II. This paper discusses the design of ELAS II.

Rickman, D.↗

NASA NTRS2001

Detection and Characterization of Imperfections in Composite Pressure Vessels

The thermographic evaluation of composite structures for delaminations, disbonds, inclusions, porosity and microcracking has proven to be a valuable asset in the field of nondestructive testing. Coupling large area coverage, variable sensitivity and minimal surface contact with a photographic type image representation of structural anomalies; thermography has become a primary inspection method for composite structures. Thermography works well for locating both surface and subsurface defects in most composite systems ranging in thickness of up to 0.25 inch (0.64 cm) or more. The thermographic method for inspection of composite structures typically involves applying an external source of heat to the structure and then recording the changes in the surface heat profile manifested by embedded defects or by material property variations. If these temperature variations are large enough and an infrared camera with sufficient sensitivity is used, then the material or structural abnormality can be detected and referred back to its source. Interpreting the information given in a thermogram, can be a difficult task under ideal circumstances and extremely challenging in a real world setting. Variables including depth, thermal conductivity, orientation and size of the abnormality can all have a great influence on how its heat pattern will be seen by the imager. The work discussed in this paper illustrates how the microstructure of several commonly found defects in composite structures relate to their thermographic image counterpart. Two test cases are studied herein, including a large graphite/epoxy RP-1 fuel tank and a graphite composite cryogenic fuel feedline. The structures used in this study were designed to serve as manufacturing proof of concept specimens and to undergo hydroburst testing to verify manufacturing practices and structural design. Prior to hydrostatic testing the structures underwent 100% thermographic evaluation to ensure that no manufacturing or handling damage was present. Due to a large inclusion found in the feedline, it was pulled from service and dissected without performing the hydroproof The thermographic indications found in the RP-1 tank were below critical limits so it underwent a complete hydroproof loading series and finally a hydroburst. Following the hydroburst samples were cut from the tank in regions where thermography had located damage before the test. These regions were thermographically and then were cross-sectioned and photomicrographed.

Walker, James L.↗

NASA NTRS2003

Developing A Contoured Deposition Head for In-Situ Tape Laying and Fiber Placement

A conformable compaction system employing three individual compactors has been designed for integration into fiber placement and tape laying deposition heads for out-of-autoclave fabrication of thermoplastic contoured parts. The compactors are intended to perform against two geometry specifications: (1) a general minimum radius of curvature limit of 180cm (71-in), and (2) a pad-up specification with a maximum height of 2.5mm (0.1-in) and a minimum ramp of 2.5mm (1-in). The mirrored specification is applicable to a pan-down. The three designs include a hot line compactor capable of a 1000N (400-lb) force at 450C over a 114mm (4.5-in) width, a hot area compactor capable of a 400N (100-lb) force at 450C over a 114mm width by 76mm length (4.5-in by 3-in), and a cold compactor that combines the features of a line and an area compactor. The cold compactor s line segments act with a 2800N (700-lb) force across a 127mm (5-in) width, while the cold compactor's area segments act with a 1000N (250-lb) force over a 127mm by 102mm (5-in by 4-in) area. Two of the designs, the hot line and hot area compactors, have been constructed, developed, and proven out in hot mode to compact actual thermoplastic composite plies over undulating geometry. IM-7PEEK [0/90/0/90]s pan-down and IM-7PEEK [0/-45/90/45]2s pad-up laminates have been fabricated and photomicrographs show good microstructure.

Lamontia, Mark A.↗

NASA NTRS2003

X-33 LH2 Tank Failure Investigation Findings

This viewgraph presentation provides information on the composite sandwich-honeycomb structure of the liquid hydrogen tank of the X-33 reusable launch vehicle, and describes why the the first pressure test to determine the tank's structural integrity failed. The presentation includes images of the tank before and after the failed test, including photomicrographs. It then reaches conclusions on the nature of the microcracks which caused the liquid hydrogen leakage.

Niedermeyer, Melinda↗

NASA NTRS1989

Localization and pattern of graviresponse across the pulvinus of barley Hordeum vulgare

Pulvini of excised stem segments from barley (Hordeum vulgare cv Larker') were pretreated with 1 millimolar coumarin before gravistimulation to reduce longitudinal cell expansion and exaggerate radial cell enlargement. The cellular localization and pattern of graviresponse across individual pulvini were then evaluated by cutting the organ in cross-section, photographing the cross-section, and then measuring pulvinus thickness and the radial width of cortical and epidermal cells in enlargements of the photomicrographs. With respect to orientation during gravistimulation, we designated the uppermost point of the cross-section 0 degrees and the lowermost point 180 degrees. A gravity-induced increase in pulvinus thickness was observable within 40 degrees of the vertical in coumarin-treated pulvini. In upper halves of coumarin-treated gravistimulated pulvini, cells in the inner cortex and inner epidermis had increased radial widths, relative to untreated gravistimulated pulvini. In lower halves of coumarin-treated pulvini, cells in the central and outer cortex and in the outer epidermis showed the greatest increase in radial width. Cells comprising the vascular bundles also increased in radial width, with this pattern following that of the central cortex. These results indicate (a) that all cell types are capable of showing a graviresponse, (b) that the graviresponse occurs in both the top and the bottom of the responding organ, and (c) that the magnitude of the response increases approximately linearly from the uppermost point to the lowermost. These results are also consistent with models of gravitropism that link the pattern and magnitude of the graviresponse to graviperception via statolith sedimentation.

Non-NASA Center↗

NASA NTRS1996

Mineralization of collagen may occur on fibril surfaces: evidence from conventional and high-voltage electron microscopy and three-dimensional imaging

The interaction between collagen and mineral crystals in the normally calcifying leg tendons from the domestic turkey, Meleagris gallopavo, has been investigated at an ultrastructural level with conventional and high-voltage electron microscopy, computed tomography, and three-dimensional image reconstruction methods. Specimens treated by either aqueous or anhydrous techniques and resin-embedded were appropriately sectioned and regions of early tendon mineralization were photographed. On the basis of individual photomicrographs, stereoscopic pairs of images, and tomographic three-dimensional image reconstructions, platelet-shaped crystals may be demonstrated for the first time in association with the surface of collagen fibrils. Mineral is also observed in closely parallel arrays within collagen hole and overlap zones. The mineral deposition at these spatially distinct locations in the tendon provides insight into possible means by which calcification is mediated by collagen as a fundamental event in skeletal and dental formation among vertebrates.

NASA Discipline Musculoskeletal↗