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  • Other Sources  (85)
  • INSTRUMENTATION AND PHOTOGRAPHY  (48)
  • STRUCTURAL MECHANICS  (37)
  • Humans
  • 1985-1989  (85)
  • 1988  (85)
  • 1
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    Deformations and strains in a thick adherend lap joint (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-27
    Description: Displacement fields in a thick adherend lap joint were measured by high-sensitivity moire interferometry. Contour maps of in-plane U and V displacements were obtained across adhesive and adherend surfaces. Loads ranged from a modest load to a near-failure load. Quantitative results are given for displacements and strains in the adhesive and along the adhesive/adherend boundary lines. The results show nearly constant shear strain in the adhesive, nonlinear strains as a function of load or average shear stress, and viscoelastic or time-dependent response. Longitudinal normal strains in the adhesive are nearly two orders of magnitude less than the shear strains. With its subwavelength displacement resolution and high spatial resolution, moire interferometry is especially well suited for deformation studies of adhesive joints.
    Keywords: STRUCTURAL MECHANICS
    Type: International Symposium on Adhesively Bonded Joints; Testing, Analysis, and Design; Sept. 10-12, 1986; Baltimore, MD; United States
    Format: text
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  • 2
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    Advanced altimetry (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The radar altimeter being developed for the Ocean Topography Experiment (TOPEX) will have an inherent instrument precision of 2 to 3 cm. While some minor refinements may be possible in the future, major geophysical advances could be made if altimetric measurements over a wide swath of the Earth's surface were possible. The NASA Headquarters Oceanic Processes Branch is supporting a 3-year investigation of the technological issues inherent in the precision measurement of topography from spaceborne platforms at angles off-nadir. To explore the off-nadir measurement of topography, a flexible, airborne radar instrument system is being developed. Its hardware design is now complete, and it is made up of several subsystems. The antenna selected is a dielectric lens of .894 m diameter. The RF subsystem uses phase-locked oscillators, FET solid-state amplifiers, and times four frequency multipliers to develop a transmit signal at a frequency of 36.0 GHz and a local oscillator signal at a frequency of 35.4 GHz. Lecroy 6880 digitizers under computer control digitize the five receiver outputs. The digital subsystem consists of six single-board Heurikon processors. At this time, the instrument construction continues with final system integration planned for November 1988.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Laboratory for Oceans; p 45-47
    Format: application/pdf
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  • 3
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    A theory of viscoplasticity accounting for internal damage (1988)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: A constitutive theory for use in structural and durability analyses of high temperature isotropic alloys is presented. Constitutive equations based upon a potential function are determined from conditions of stability and physical considerations. The theory is self-consistent; terms are not added in an ad hoc manner. It extends a proven viscoplastic model by introducing the Kachanov-Rabotnov concept of net stress. Material degradation and inelastic deformation are unified; they evolve simultaneously and interactively. Both isotropic hardening and material degradation evolve with dissipated work which is the sum of inelastic work and internal work. Internal work is a continuum measure of the stored free energy resulting from inelastic deformation.
    Keywords: STRUCTURAL MECHANICS
    Type: Nonlinear Constitutive Relations for High Temperature Applications, 1986; p 119-136
    Format: application/pdf
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  • 4
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    Two-mirrored galvanometer laser light sheet generator (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: Light sheets generated with either laser or noncoherent sources have found widespread application to flow visualization. Previous light sheet generating systems were usually dedicated to a specific viewing geometry. The technique with the most flexibility is the galvanometer mirror based laser light sheet system. A two-mirrored system was designed and developed to provide flexibility and adaptability to a wide range of applications. The design includes the capability to control the size and location of the laser light sheet in real time, to generate horizontal or vertical sheets, to sweep the sheet repeatedly through a volume, to generate multiple sheets with controllable separation and to rotate single or multiple laser light sheets. The system is capable of producing up to 12 sheets of laser light at an angular divergence of + or - 20 degrees. Maximum scan rate of any one line is 500 Hertz. This system has proven to be uniquely versatile and a patent has been applied for.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: AIAA PAPER 88-4680
    Format: text
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  • 5
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    Effects of subcritical crack growth on fracture toughness of ceramics assessed in chevron-notched three-point bend tests (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: A numerical computational study was carried out to assess the effects of subcritical crack growth on crack stability in the chevron-notched three-point bend specimens. A power-law relationship between the subcritical crack velocity and the applied stress intensity were used along with compliance and stress-intensity relationships for the chevron-notched bend specimen to calculate the load response under fixed deflection rate and a machine compliance. The results indicate that the maximum load during the test occurs at the same crack length for all the deflection rates; the maximum load, however, is dependent on the deflection rate for rates below the critical rate. The resulting dependence of the apparent fracture toughness on the deflection rate is compared to experimental results on soda-lime glass and polycrystalline alumina.
    Keywords: STRUCTURAL MECHANICS
    Type: ASME PAPER 88-GT-185
    Format: text
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  • 6
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    Direct and interferometric imaging approaches for detecting earth-like extrasolar planets (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: This paper discusses functional requirements of space-based observational systems with sufficient sensitivity, resolution, and dynamic range to image earth-like extrasolar planets within a search radius of 10 parsecs from the sun. Both direct and interferometric systems operating at visible and infrared wavelengths are evaluated, and the methods used to establish the system tolerances are presented. Due to the more favorable star/planet contrast ratio in the infrared, optical tolerance requirements are less stringent than in the visible. However, reduction of thermal radiation from the telescope requires cooling of the primary optics. Other tradeoffs between various approaches are enumerated.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: AIAA PAPER 88-0553
    Format: text
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  • 7
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    Experimental comparison of two hot-wire techniques for resolution of turbulent mass flux and local stagnation temperature in supersonic flow (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-06-28
    Description: The performance of two constant-temperature normal hot-wire techniques in a supersonic flow is examined. The first technique uses a single-wire and rapid scanning of multiple overheat ratios. Time averages of the signals at all overheats are used to separate the mean and rms mass flux, stagnation temperature and their cross-correlation. The second technique uses a dual-wire probe with each wire operating at different overheat ratios, giving instantaneous mass flux and stagnation temperature. Preliminary results indicate that the separation distance (0.18 mm) between the two hot wires in the dual-wire probe does not introduce significant error. However, the rms mass flux inferred from the dual-wire technique is a factor of two higher than that from the single-wire technique.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: AIAA PAPER 88-0422
    Format: text
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  • 8
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    Calibration of single particle sizing velocimeters using photomask reticles (1988)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The development of photomask reticle calibration standards for single particle instruments is discussed. The calibration method studied involves the use of photomask reticles where the particle artifacts are actually disks of chrome thin film in the clear field reticles produced by photolithography and etching processes. Consideration is given to various aspects of theory, design, and performance.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: International Symposium on Applications of Laser Anemometry to Fluid Mechanics; Jul 11, 1988 - Jul 14, 1988; Lisbon; Portugal
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  • 9
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    A proposed method for enhanced eigen-pair extraction using finite element methods: Theory and application (1988)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: The paper covers two distinct parts: theory and application. The goal of this work was the reduction of model size with an increase in eigenvalue/vector accuracy. This method is ideal for the condensation of large truss- or beam-type structures. The theoretical approach involves the conversion of a continuum transfer matrix beam element into an 'Exact' dynamic stiffness element. This formulation is implemented in a finite element environment. This results in the need to solve a transcendental eigenvalue problem. Once the eigenvalue is determined the eigenvectors can be reconstructed with any desired spatial precision. No discretization limitations are imposed on the reconstruction. The results of such a combined finite element and transfer matrix formulation is a much smaller FEM eigenvalue problem. This formulation has the ability to extract higher eigenvalues as easily and as accurately as lower eigenvalues. Moreover, one can extract many more eigenvalues/vectors from the model than the number of degrees of freedom in the FEM formulation. Typically, the number of eigenvalues accurately extractable via the 'Exact' element method are at least 8 times the number of degrees of freedom. In contrast, the FEM usually extracts one accurate (within 5 percent) eigenvalue for each 3-4 degrees of freedom. The 'Exact' element results in a 20-30 improvement in the number of accurately extractable eigenvalues and eigenvectors.
    Keywords: STRUCTURAL MECHANICS
    Type: JPL, Model Determination for Large Space Systems, Volume 3; 33 p
    Format: text
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  • 10
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    Response function of a tunable diode laser spectrometer from an iterative deconvolution procedure (1988)
    In:  Other Sources
    Details
    Publication Date: 2011-08-19
    Description: A deconvolution procedure commonly used for resolution enhancement of spectra has been applied to the determination of the response function of a tunable diode laser spectrometer. The method is sufficiently fast and simple for routine application when correcting for nonnegligible instrumental broadening. Absolute linestrengths of CH4 in the 1327/cm region and line positions of HNO3 in the 1335/cm region, measured with the aid of the deconvolution technique, are reported here.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Type: Journal of Quantitative Spectroscopy and Radiative Transfer (ISSN 0022-4073); 39; 247-253
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