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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

Use of Computed Tomography for Characterizing Materials Grown Terrestrially and in Microgravity

Computed Tomography (CT) has advanced considerably since being responsible for such dramatic advances in diagnostics within the medical field. It has become a major tool in non destructive evaluation (NDE), and is used in many fields as diverse as coal-mining to metal solidification to examination of rock cores. A review of industrial applications has been written by Dennis. It is only recently that the technique has been seriously used to determine composition through precise measurement of density. While such applications are restricted to cases when there is no ambiguity in the relationship of composition to density. Thus alloy solid solutions lend themselves to compositional analysis provided there is a large change in density with composition. The technique is most useful when rapid non-destructive evaluation is needed. Such cases will occur with samples returning from the International Space Station (ISS) when knowledge of the results could affect future strategies for processing of on-board samples. Experiments from those Principal Investigators (PI) that are most likely to benefit from early CT scanning are discussed. With a dearth of samples, the major emphasis in the first part of this project has been on preparing suitable standards, optimizing the CT technique for these applications, and using the CT system to determine density variations with temperature. An interesting application of CT has been in the examination of meteorites, which can be classified as space-grown materials and will certainly have solidified in a low gravity environment.

Gillies, Donald C.↗
NASA NTRS1988

Asteroid team

The purpose of this task is to support asteroid research and the operation of an Asteroid Team within the Earth and Space Sciences Division at the Jet Propulsion Laboratory (JPL). The Asteroid Team carries out original research on asteroids in order to discover, better characterize and define asteroid properties. This information is needed for the planning and design of NASA asteroid flyby and rendezvous missions. The asteroid Team also provides scientific and technical advice to NASA and JPL on asteroid related programs. Work on asteroid classification continued and the discovery of two Earth-approaching M asteroids was published. In the asteroid photometry program researchers obtained N or Q photometry for more than 50 asteroids, including the two M-earth-crossers. Compositional analysis of infrared spectra (0.8 to 2.6 micrometer) of asteroids is continuing. Over the next year the work on asteroid classification and composition will continue with the analysis of the 60 reduced infrared spectra which we now have at hand. The radiometry program will continue with the reduction of the N and Q bandpass data for the 57 asteroids in order to obtain albedos and diameters. This year the emphasis will shift to IRAS follow-up observations; which includes objects not observed by IRAS and objects with poor or peculiar IRAS data. As in previous year, we plan to give top priority to any opportunities for observing near-Earth asteroids and the support (through radiometric lightcurve observations from the IRTF) of any stellar occultations by asteroids for which occultation observation expeditions are fielded. Support of preparing of IRAS data for publication and of D. Matson for his participation in the NASA Planetary Astronomy Management and Operations Working Group will continue.

Matson, D. L.↗
NASA NTRS1974

Nonlinear finite-element analysis of laminated composite shells

Two aspects of the geometrically nonlinear analysis of laminated composite shells are considered in this paper. The first pertains to the simplifications and computational advantages resulting from the use of group-theoretic methods in conjunction with computerized symbolic (algebraic) manipulation in the element development. The second aspect pertains to the combined effects of shear deformation and nonlinearity on the accuracy and convergence of two-dimensional, shear-flexible stiffness finite element models.

Noor, A. K.↗
NASA NTRS1996

Two-Flux Green's Function Analysis for Transient Spectral Radiation in a Composite

An analysis is developed for obtaining transient temperatures in a two-layer semitransparent composite with spectrally dependent properties. Each external boundary of the composite is subjected to radiation and convection. The two-flux radiative transfer equations are solved by deriving a Green's function. This yields the local radiative heat source needed to numerically solve the transient energy equation. An advantage of the two-flux method is that isotropic scattering is included without added complexity. The layer refractive indices are larger than one. This produces internal reflections at the boundaries and the internal interface; the reflections are assumed diffuse. Spectral results using the Green's function method are verified by comparing with numerical solutions using the exact radiative transfer equations. Transient temperature distributions are given to illustrate the effect of radiative heating on one side of a composite with external convective cooling. The protection of a material from incident radiation is illustrated by adding scattering to the layer adjacent to the radiative source.

Siegel, Robert↗
NASA NTRS1993

Thin film processing of photorefractive BaTiO3

During the period covered by this report, October 11, 1991 through October 10, 1992, the research has progressed in a number of different areas. The sol-gel technique was initially studied and experimentally evaluated for depositing films of BaTiO3. The difficulties with the precursors and the poor quality of the films deposited lead to the investigation of pulsed laser deposition as an alternative approach. The development of the pulsed laser deposition technique has resulted in continuous improvements to the quality of deposited films of BaTiO3. The initial depositions of BaTiO3 resulted in amorphous films, however, as the pulsed laser deposition technique continued to evolve, films were deposited in the polycrystalline state, then the textured polycrystalline state, and most recently heteroepitaxial films have also been successfully deposited on cubic (100) oriented SrTiO3 substrates. A technique for poling samples at room temperature and in air is also undergoing development with some very preliminary but positive results. The analytical techniques, which include x-ray diffraction, ferroelectric analysis, UV-Vis spectrophotometry, scanning electron microscopy with x-ray compositional analysis, optical and polarized light microscopy, and surface profilometry have been enhanced to allow for more detailed evaluation of the samples. In the area of optical characterization, a pulsed Nd:YAG laser has been incorporated into the experimental configuration. Now data can also be acquired within various temporal domains resulting in more detailed information on the optical response of the samples and on their photorefractive sensitivity. The recent establishment of collaborative efforts with two departments at Johns Hopkins University and the Army Research Lab at Fort Belvoir has also produced preliminary results using the metallo-organic decomposition technique as an alternative method for thin film processing of BaTiO3. RF and DC sputtering is another film deposition approach that should be initiated in the near future. Other techniques for optical characterization, which may even allow for intragrannular (within single grains) investigations, are also being considered.

Schuster, Paul R.↗
NASA NTRS2001

High Fidelity Failure Analysis for a Composite Fuselage Section

A high fidelity delamination failure analysis was developed by combining a local failure analysis with a global full-scale finite element structural analysis to address strength and delamination failure in a single package. The methodology was demonstrated through a local three-dimensional pull-off failure analysis and a geometrically nonlinear structural analysis of a five-foot composite helicopter fuselage section. Pull-off specimens were used to identify potential debonding failure of co-cured skin-stringer/frame fuselage structures. An investigation of the failed pull-off specimens was performed to determine the location of the failure initiation. Three-dimensional strain energy release rate analysis indicates that the delamination initiation and growth is controlled by Mode 1 opening mode. The bending moment at the delamination tip was identified as the crucial factor controlling the failure. The geometrically nonlinear structural analysis of a five-foot composite fuselage section was performed using a detailed finite element model. Loads were applied along the periphery of the subcomponent using displacement fields generated from solutions of a full-vehicle model.

Li, Jain↗
NASA NTRS2002

Energy Dispersive Spectrometry and Quantitative Analysis Short Course. Introduction to X-ray Energy Dispersive Spectrometry and Quantitative Analysis

This course will cover practical applications of the energy-dispersive spectrometer (EDS) to x-ray microanalysis. Topics covered will include detector technology, advances in pulse processing, resolution and performance monitoring, detector modeling, peak deconvolution and fitting, qualitative and quantitative analysis, compositional mapping, and standards. An emphasis will be placed on use of the EDS for quantitative analysis, with discussion of typical problems encountered in the analysis of a wide range of materials and sample geometries.

Carpenter, Paul↗
NASA NTRS1987

Fatigue damage accumulation in various metal matrix composites

The purpose of this paper is to review some of the latest understanding of the fatigue behavior of continuous fiber reinforced metal matrix composites. The emphasis is on the development of an understanding of different fatigue damage mechanisms and why and how they occur. The fatigue failure modes in continuous fiber reinforced metal matrix composites are controlled by the three constituents of the system: fiber, matrix, and fiber/matrix interface. The relative strains to fatigue failure of the fiber and matrix will determine the failure mode. Several examples of matrix, fiber, and self-similar damage growth dominated fatigue damage are given for several metal matrix composite systems. Composite analysis, failure modes, and damage modeling are discussed. Boron/aluminum, silicon-carbide/aluminum, FP/aluminum, and borsic/titanium metal matrix composites are discussed.

Johnson, W. S.↗
NASA NTRS1977

A technique to correct for sample thickness variations for use with IDAPS X-ray radiograph analysis

The Image Data Processing System (IDAPS) at the Marshall Space Flight Center is used to analyze radiographs of metal samples to qualitatively and quantitatively map compositional variations across the samples. When the X-ray radiographs are of samples having thickness variations, corrections must be made to accomplish compositional analysis. A correction technique is described for cylindrical samples and is applied to radiographs of SPAR Experiment 74-18. Uncorrected and corrected images are shown.

Schafer, C. F.↗
NASA NTRS1984

Composite structural materials

Progress is reported in studies of constituent materials composite materials, generic structural elements, processing science technology, and maintaining long-term structural integrity. Topics discussed include: mechanical properties of high performance carbon fibers; fatigue in composite materials; experimental and theoretical studies of moisture and temperature effects on the mechanical properties of graphite-epoxy laminates and neat resins; numerical investigations of the micromechanics of composite fracture; delamination failures of composite laminates; effect of notch size on composite laminates; improved beam theory for anisotropic materials; variation of resin properties through the thickness of cured samples; numerical analysis composite processing; heat treatment of metal matrix composites, and the RP-1 and RP2 gliders of the sailplane project.

Ansell, G. S.↗
NASA NTRS1991

Micromechanical analysis of the failure process in ceramic matrix composites

An analysis of the effectiveness of fiber reinforcement in brittle matrix composites is presented. The analytical method allows consideration of discrete fiber distribution and examination of the development of crack growth parameters on the microscale. The problem associated with bridging zone development is addressed here; therefore, the bridging zone is considered to be smaller than the main preexisting crack, and the small scale approach is used. The mechanics of the reinforcement is accurately accounted for in the process zone of a growing crack. Closed form solutions characterizing the initial failure process are presented for linear and nonlinear force-fiber pullout displacement relationships. The implicit exact solution for the extended bridging zone is presented as well.

Rubinstein, Asher A.↗
NASA NTRS1984

A simple rectangular element for 2-dimensional analysis of laminated composites

A simple rectangular finite element was developed for two dimensional analysis of laminated composite materials. The rectangular laminated composite element eliminates the need to add elements to a model simply to account for the material properties of various laminae. This is particularly advantageous for thick laminates with many lamina. Explicit integration in terms of generalized displacements minimizes the algebraic effort required to derive the element stiffness and the thermal load vector. A substitute shape function technique is used to improve the performance of the element in modeling bending type deformation. Results for several example problems are discussed.

Whitcomb, J. D.↗
NASA NTRS1989

Structural tailoring of laminate properties

In this study, structural synthesis techniques have been applied to tailor the composite laminate properties from the micromechanics to the laminate level for a desirable structural response. It is also demonstrated how to establish upper and lower bounds on design variables based on reliability considerations. The question of reliability arises in fiber composite analysis and design because of the inherent scatter that is observed in the constituent material properties in the experimental data. The symmetric composite laminates subject to mechanical loading are considered and no hygrothermal effects are taken into account in the present research. Application examples illustrate the effects of various ply and laminate parameters on the overall properties and structural response of composite laminates.

Thanedar, P. B.↗
NASA NTRS1993

Thermomechanical postbuckling analysis of laminated composite shells

The nonlinear response of laminated composite structures subjected to thermal loads is investigated. Analysis is performed using a refined theory and an associated finite element model for geometrically nonlinear analysis of laminated composite shell structures. The model is based on a third-order displacement field which accounts for both transverse shear and transverse normal deformations. Numerical studies of simply-supported plates and cylindrical panels indicate that when the panels are free to expand or contract in the transverse direction, the predicted critical buckling temperatures do not depend significantly upon whether or not transverse normal deformations are explicitly accounted for in the analysis model. However, the critical buckling temperatures are strongly dependent upon whether or not the transverse normal deformations are restrained along the boundaries of the panels.

Averill, R. C.↗
NASA NTRS1989

Preliminary examination of the Yamato-86032 lunar meteorite. II - Major and trace element chemistry

Results of the chemical composition analysis of Yamato-86032, found in Antarctica in 1986, are summarized. The meteorite may be classified as an anorthositic breccia, but its trace element composition is different from the composition of the other known lunar meteorites. The major element chemistry of Y-86032 is similar to the other lunar meteorites, except for the iron content, which is lower by a factor of about 1.4. The abundances of incompatible and lithophile elements such as Zr, Hf, Ta, Th, or the REEs are very low and comparable to Y-82192/3. Other elements, in particular Fe, Ti, Sc, Cr, Mn, and Co, have lower abundances in Y-86032 than in Y-82192/3. Variations between individual analysis demonstrate that the rock itself is heterogeneous.

Koeberl, Christian↗
NASA NTRSDate not supplied

Ion Gun for In Situ Resource Identification

Identification of surface resources localized to landing sites is a critical need for future lunar exploration. Crews will need small, lightweight instrumentation that can be easily carried to identify potential resources in situ without extraction of samples for testing. This project aimed to conduct a proof-of-concept of using ion sputtering coupled with mass spectroscopy to provide in situ composition analysis of surface materials with no need to collect and/or return samples. Ion beam sputtering is a mature ground-based technique that ablates material surfaces for analysis.

ion sputtering↗