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  • 1
    Electronic Resource
    Electronic Resource
    Eddy-current induction in a uniaxially anisotropic plate (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 3080-3090 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A theoretical model is presented to describe the time-harmonic electromagnetic induction of eddy currents in a uniaxially anisotropic plate. The model assumes that the plate is nonmagnetic and that the axis of uniaxial anisotropy is horizontal (i.e., lying in a plane parallel to the surface of the plate). The fields and currents induced by a general magnetic source are obtained by formulating the problem in terms of reduced electromagnetic potentials (Hertzian potentials) and making extensive use of integral transforms. Closed-form expressions for the reduced potentials are given explicitly, enabling the induced fields to be calculated in all regions provided the free-space source fields are known. The change in probe-coil impedance ΔZ due to eddy-current induction is considered in detail, and an explicit closed-form expression for ΔZ is derived for the general case. This general theory is illustrated by calculating ΔZ for a cylindrical air-cored coil when (i) the coil axis is normal to the surface of the plate and (ii) the coil axis is tangential to the surface of the plate. The validity of these calculations was established by performing a series of measurements of ΔZ using an aluminum-alloy sheet unidirectionally reinforced with boron fibers. The results of the theoretical calculations are in excellent agreement with experiment. The significance of the results for the nondestructive characterization of metal-matrix composite materials is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347171
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  • 2
    Electronic Resource
    Electronic Resource
    Eddy-current inversion in the thin-skin limit: Determination of depth and opening for a long crack (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 3072-3080 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A method for crack size determination using eddy-current nondestructive evaluation is presented for the case of a plate containing an infinitely long crack of uniform depth and uniform crack opening. The approach is based on the approximate solution to Maxwell's equations for nonmagnetic conductors in the limit of small skin depth and relies on least-squares polynomial fits to a normalized coil impedance function as a function of skin depth. The method is straightforward to implement and is relatively insensitive to both systematic and random errors. The procedure requires the computation of two functions: a normalizing function, which depends both on the coil parameters and the skin depth, and a crack-depth function which depends only on the coil parameters in addition to the crack depth. The practical performance of the method was tested using a set of simulated cracks in the form of electro-discharge machined slots in aluminum alloy plates. The crack depths and crack opening deduced from the eddy-current measurements agree with the actual crack dimensions to within 10% or better. Recommendations concerning the optimum conditions for crack sizing are also made.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.358454
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  • 3
    Electronic Resource
    Electronic Resource
    Novel approach for detecting distributed surface-breaking cracks (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 65 (1994), S. 1349-1351 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A novel approach to the problem of detecting finely distributed surface cracks in a structure is proposed. The approach relies on the detection of anisotropy introduced into the surface by an oriented array of cracks and can be used for crack detection even when individual cracks in the array are below the practical threshold of detectability by conventional inspection techniques. The feasibility of detecting anisotropy associated with distributed cracking was established experimentally using: (i) a directional eddy-current probe to detect anisotropy in the effective electrical conductivity and (ii) a line-focused laser-ultrasonic source to detect anisotropy in the attenuation of ultrasonic Rayleigh waves.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.112048
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  • 4
    Electronic Resource
    Electronic Resource
    Eddy-current inspection of cracks in a multilayer conductor (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 465-476 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A theoretical model is presented to describe the time-harmonic induction of eddy currents in a layered conductor containing a crack. The layered system consists of two parallel conducting plates separated by an insulating gap and it is assumed that the thickness tS of the plate containing the (through-the-thickness) crack is small compared with the electromagnetic skin depth δS. Explicit expressions for the magnetic vector potential in the absence of the crack are derived for the particular case of induction by a circular air-cored coil, and these results are used to calculate the change in coil impedance ΔZU due to the induced currents in the uncracked system. The effect of a through-the-thickness crack is represented by an equivalent distribution of current sources along the line of the crack. The form of these generalized current vortex sources is examined and explicit expressions are presented for the current density and vector potential due to a single vortex. The vortex density, and hence the induced current distribution, are obtained by solving a one-dimensional singular integral equation. This formalism is used to calculate the change in coil impedance ΔZC due to a first- or second-layer crack. Experimental measurements of ΔZ were carried out for several model systems and the theoretical calculations were found to agree with experiment to within 10% or better for tS/δS up to 0.4. The implications for the detectability of cracks using eddy-current nondestructive inspection is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345227
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  • 5
    Electronic Resource
    Electronic Resource
    Superparamagnetism and the character of magnetic order in binary Cr–Fe alloys near the critical concentration (1978)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 11 (1978), S. 644-648 
    Details
    ISSN: 1600-5767
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences , Physics
    Notes: Although the magnetic properties of Cr–Fe alloys have been widely studied, there are different interpretations of existing data in the literature, especially for alloys in the concentration range 10 to 25% Fe. The onset of ferromagnetism occurs somewhere in this concentration range, but there is little direct evidence of the precise critical concentration. Detailed small-angle scattering measurements have been carried out on alloys containing 16.7, 19.9, 20.9, 21.7, 24 and 25% Fe over a wide range of temperatures and magnetic fields. Small-angle scattering peaked in the forward direction develops at low temperatures, corresponding to the growth of magnetic correlations over distances of the order of 400 Å. The response of the scattering to the application of a magnetic field suggests that the scattering at low temperatures arises from superparamagnetic clusters. Curie temperatures were deduced from the critical scattering, and the variation of Tc with composition suggests that the critical concentration is close to 19% Fe.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0021889878014120
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  • 6
    Electronic Resource
    Electronic Resource
    A benchmark problem for computation of ΔZ in eddy-current nondestructive evaluation (NDE) (1988)
    Springer
    Journal of nondestructive evaluation 7 (1988), S. 35-41 
    Details
    ISSN: 1573-4862
    Keywords: Eddy-current nondestructive evaluation (NDE) ; impedance measurement ; electromagnetic modeling
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract Experimental results are presented for the change in coil impedance ΔZ when a circular air-cored coil carrying an alternating current of fixed frequency is scanned across a rectangular slot in an aluminium alloy plate. It is proposed that these measurements be used as a benchmark test to verify theoretical calculations of probe response in eddy-current NDE.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00565775
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  • 7
    Electronic Resource
    Electronic Resource
    Benchmark problems for defect size and shape determination in eddy-current nondestructive evaluation (1996)
    Springer
    Journal of nondestructive evaluation 15 (1996), S. 21-34 
    Details
    ISSN: 1573-4862
    Keywords: Eddy-current NDE ; defect sizing ; benchmark problems ; inverse problems
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Mathematics
    Notes: Abstract A set of four benchmark problems is presented for verification of theoretical calculations of defect size and shape in eddy-current nondestructive evaluation. The benchmark problems are based on careful measurements of the change in coil impedance as a function of frequency for a circular air-cored coil which is scanned along the axis of an electrodischarge machined slot in a thick aluminum alloy plate. Slots of (i) semi-elliptical, and (ii) double-peaked profiles are considered. Deviations from ideal coil behavior are identified and corrected so that the final impedance data and experimental parameters can be directly used to verify theoretical inversion algorithms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00733823
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  • 8
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    Magnetic Excitations in the Incommensurate Phases of Chromium Metal (1983)
    American Physical Society
    Details
    Publication Date: 1983-08-08
    Print ISSN: 0031-9007
    Electronic ISSN: 1079-7114
    Topics: Physics
    Published by American Physical Society
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  • 9
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    Novel approach for detecting distributed surface‐breaking cracks (1994)
    American Institute of Physics
    Details
    Publication Date: 1994-09-12
    Print ISSN: 0003-6951
    Electronic ISSN: 1077-3118
    Topics: Physics
    Published by American Institute of Physics
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  • 10
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    Impedance of curved rectangular spiral coils around a conductive cylinder (2008)
    American Institute of Physics
    Details
    Publication Date: 2008-07-01
    Print ISSN: 0021-8979
    Electronic ISSN: 1089-7550
    Topics: Physics
    Published by American Institute of Physics
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