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  • 1
    Electronic Resource
    Electronic Resource
    Characterization of capacitive array for NDE applications (1990)
    Springer
    Research in nondestructive evaluation 2 (1990), S. 11-27 
    Details
    ISSN: 1432-2110
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract We have developed a capacitive array sensor which responds to the complex dielectric constant of an interrogated material. The sensor requires only single-sided access and operates in a differential mode for detection of discontinuities in the relative dielectric constant, ε r , or in the absolute mode where the interest is in absolute quantities. The device in general is noncontacting but can be fabricated as an embedded sensor. Various proof-of-concept studies have been performed to explore possible applications of the device. In the differential mode, small surface features (notches) were detected in a conductor; in dielectrics, both surface and subsurface features were detected. The probe was sensitive to change in impedance caused by a curing epoxy, viewed through a graphite-epoxy composite panel. A study was performed to assess the use of the probe for noncontact characterization of sintering of ceramics. In this (absolute) mode, the effects of liftoff and dielectric constant must be separated. We propose a scheme based on the ability to multiplex the capacitive array probe to accomplish this. Preliminary investigation shows that the effect of parasitic capacitance between the probe and ground points in the environment must be suppressed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01606376
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  • 2
    Electronic Resource
    Electronic Resource
    Eddy-current reflection probes: Theory and experiment (1989)
    Springer
    Research in nondestructive evaluation 1 (1989), S. 1-11 
    Details
    ISSN: 1432-2110
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A general ΔZ theory of reflection-type eddy-current probes was recently developed for new types of robotic proximity sensors. In this paper, the theory is applied to the characterization of surface-connected flaws. Flaw signals were calculated using a finite-difference implementation of the ΔZ theory developed at Stanford University. A special air-core eddy-current reflection probe was fabricated at the National Institute of Standards and Technology (NIST) and used to obtain flaw signals for a number of rectangular-shaped electrical-discharge-machined (EDM) notches in aluminum. An automatic impedance analyzer was used to measure flaw signals as the probe was scanned over the length of the flaw. Experimental results were then compared to predictions of the theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01607866
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  • 3
    Electronic Resource
    Electronic Resource
    Review of Advances in Quantitative Eddy Current Nondestructive Evaluation (1999)
    Springer
    Journal of nondestructive evaluation 18 (1999), S. 3-36 
    Details
    ISSN: 1573-4862
    Keywords: Eddy current modeling ; quantitative NDE ; reciprocity formulas ; thin skin theory ; eddy current inversion ; pulsed eddy current
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A comprehensive review of advancements in eddy current (EC) modeling is presented. This paper contains three main sections: a general treatise of EC theory, the thin skin EC forward modeling, and the EC inverse problem. (1) The general treatise of eddy current theory begins with an exposition of the reciprocity formulas for evaluating probe impedance changes, which are derivable from first principles. Two versions of the reciprocity formulas, one with a surface integral and the other with a volume integral, are given. Any particular type of defect, as well as both one-port and two-port probes, can be treated. Second, a brief account of analytical and numerical methods for calculating the field distributions is presented. Third, theory of probe/material interactions with various defect types is described. (2) The paper then proceeds to the forward modeling section, which contains a detailed treatment of the eddy current forward problem for surface breaking cracks and EDM notches in the thin skin approximation. (3) The inverse problem section begins with a general review of commonly used inversion methods, exemplified by selected references from the literature, followed by more detailed examinations of EC inversions for surface breaking cracks and slots. The last part of this section is devoted to the inverse problem for layered structures. Although being a review in nature, the paper contains a number of new accounts for time-domain eddy current interactions. In particular, a modification is proposed to the reciprocity formula in order to take a better account of pulsed eddy current signals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1023/A:1021898520626
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  • 4
    Electronic Resource
    Electronic Resource
    Eddy-current signal analysis and inversion for semielliptical surface cracks (1988)
    Springer
    Journal of nondestructive evaluation 7 (1988), S. 79-94 
    Details
    ISSN: 1573-4862
    Keywords: Eddy current ; finite-difference method ; flaw characterization ; inversion ; nondestructive evaluation ; scalar potential
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A scalar potential formulation of the δZ formula for the change in impedance of an eddy-current probe caused by a surface-breaking flaw is developed. The resulting formula is evaluated using a finite-difference method, which permits calculation of δZ for semielliptical flaws. The numerical results are checked by comparing calculations for rectangular-shaped flaws to previous calculations using an analytical solution for this geometry. Theoretical results are then verified by comparison with measurements on semielliptical fatigue cracks and EDM notches in aluminum alloy specimens using air-core eddy-current probes. An inversion method that compares features of the flaw profile, obtained by scanning the eddy-current probe along the length of the flaw, to a theoretical inversion chart (McFetridge chart) is demonstrated using the experimental data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00565779
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  • 5
    Electronic Resource
    Electronic Resource
    Experimental study of path independence of theJ integral in an aluminum tensile panel (1987)
    Springer
    Experimental mechanics 27 (1987), S. 328-332 
    Details
    ISSN: 1741-2765
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract A newly devised video-optical experimental technique allows for the automated determination of the in-plane, plane-stress components of the infinitesimal deformation tensor at discrete locations over an area of interest in a loaded specimen. It was used to evaluate a square area enclosing the central crack in a 5052-H32 aluminum panel loaded in tension. These experimental strain-tensor values were then used to evaluate theJ integral assuming that the mechanical behavior of the plate material is approximated by deformation plasticity theory. TheJ integral was evaluated using two series of rectangular paths. The first was symmetrical about a horizontal axis passing through the notch length, using strain-tensor values at points to the left and right of a vertical axis passing through the center of the notch, with varying breadth and height. The second series were asymmetrical about either axis, with varying breadth and height. The latter paths served to evaluate the experimental error associated with each of the four quadrants of the plate. TheJ integral is found to be path independent within the range of experimental error associated with the video-optical experimental-measurement technique. An independent verification of theJ integral value is obtained using a calculation related to the crack-mouth-opening displacement (CMOD). It is found to agree well with the values obtained by this new procedure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02318099
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  • 6
    Electronic Resource
    Electronic Resource
    Simulation of capacitive array sensors using finite and infinite elements (1989)
    Chichester [u.a.] : Wiley-Blackwell
    International Journal of Numerical Modelling: Electronic Networks, Devices and Fields 2 (1989), S. 117-129 
    Details
    ISSN: 0894-3370
    Keywords: Engineering ; Electrical and Electronics Engineering
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Electrical Engineering, Measurement and Control Technology
    Notes: The response of capacitive array sensors in the presence of flawed solid materials is simulated using finite elements and infinite elements with exponential decay. Conventional finite elements are used to model the critical regions near the probe and the surface of the solid. Infinite elements are used to represent the farfield conditions of the space surrounding the probe and the solid. The method is first applied to problems with analytic solutions to determine the accuracy of the results obtained using the infinite elements. The response of a capacitive array sensor is then simulated using a line integral which measures the relative change in admittance between flawed and unflawed solids. Examples of capacitive probe responses are given for several parametric variations of the flaw size and dielectric constant of the solid.
    Additional Material: 13 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/jnm.1660020303
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  • 7
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    Experimental study of path independence of theJ integral in an aluminum tensile panel (1987)
    Springer
    Details
    Publication Date: 1987-09-01
    Print ISSN: 0014-4851
    Electronic ISSN: 1741-2765
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Published by Springer
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    PAPER CURRENT
  • 8
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    Experimental determination of the near-surface conductivity profiles of metals from electromagnetic induction (eddy current) measurements (1994)
    Institute of Physics
    Details
    Publication Date: 1994-06-01
    Print ISSN: 0266-5611
    Electronic ISSN: 1361-6420
    Topics: Mathematics , Physics
    Published by Institute of Physics
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    PAPER CURRENT
  • 9
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    Time-resolved spectra of bulk titanium combustion (1974)
    In:  Other Sources
    Details
    Publication Date: 2019-06-27
    Description: Some preliminary spectroscopic results of an investigation of the radiation from bulk specimens of burning titanium are presented. The use of larger stationary specimens is shown to have considerably eased some of the experimental difficulties associated with metal combustion research and to approximate more closely the conditions prevailing in large-scale accidental metal fires.
    Keywords: THERMODYNAMICS AND COMBUSTION
    Type: Combustion and Flame; 23; Aug. 197
    Format: text
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    NASA TECHNICAL REPORTS
  • 10
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    Combustion of bulk titanium in oxygen (1975)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The combustion of bulk titanium in one atmosphere oxygen is studied using laser ignition and several analytical techniques. These were high-speed color cinematography, time and space resolved spectra in the visible region, metallography (including SEM) of specimens quenched in argon gas, X-ray and chemical product analyses, and a new optical technique, the Hilbert transform method. The cinematographic application of this technique for visualizing phase objects in the combustion zone is described. The results indicate an initial vapor phase reaction immediately adjacent to the molten surface but as the oxygen uptake progresses the evaporation approaches the point of congruency and a much reduced evaporation rate. This and the accumulation of the various soluble oxides soon drive the reaction zone below the surface where gas formation causes boiling and ejection of particles. The buildup of rutile cuts off the oxygen supply and the reaction ceases.
    Keywords: METALLIC MATERIALS
    Type: International Symposium on Combustion; Aug 25, 1974 - Aug 31, 1974; Tokyo; Japan
    Format: text
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    NASA TECHNICAL REPORTS
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