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Characterisation of surface and sub-surface discontinuities in metals using pulsed eddy current sensors

Sophian, Ali (2003) Characterisation of surface and sub-surface discontinuities in metals using pulsed eddy current sensors. Doctoral thesis, University of Huddersfield.

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    Abstract

    Due primarily to today's rigorous safety standards the focus of non-destructive testing
    (NDT) has shifted from flaw detection to quantitative NIDT, where characterisation of
    flaws is the objective. This means information such as the type of flaw and its size is
    desired. The Pulsed Eddy Current (PEC) technique has been acknowledged as one of the
    potential contenders for providing this additional functionality, due to the potential
    richness of the information that it provides. The parameters mainly used to obtain
    information about the detected flaws are the signal's peak height and arrival time.
    However, it has been recognised that these features are not sufficient for defect
    classification. In this research, based on a comprehensive literature survey, the design of
    PEC systems and the interpretation of PEC signals, mainly for flaw classification, are
    studied.
    A PEC system consisting of both hardware and software components has been designed
    and constructed to facilitate the research work on PEC signal interpretation. After a
    comparative study of several magnetic sensing devices, probes using Hall device magnetic
    sensors have also been constructed. Some aspects related to probe design, such as coil
    dimensions and the use of ferrite core and shielding have also been studied.
    A new interpretation technique that uses the whole part of PEC responses and is able to
    produce more features has been proposed. The technique uses Principal Component
    Analysis (PCA) and Wavelet Transforms, and attempts to find the best features for
    discrimination from extracted time and frequency domain data. The simultaneous use of
    both temporal and spectral data is a logically promising extension to the use of time
    domain only with the signal-peak-based technique. Experiments show that the new 1 technique is promising as it performs significantly better than the conventional technique using peak value and peak time of PEC signals in the classification of flaws. A hierarchical
    structure for defect classification and quantification has been presented.
    Experiments in the project have also shown that the signal-peak-based technique cannot be
    used for flaw detection and characterisation in steels, both with and without magnetisation.
    The new proposed technique has shown to have potential for this purpose when
    magnetisation is used. The new technique proposed in the report has been successfully
    used for ferromagnetic and non-ferromagnetic materials. It has also been demonstrated that
    the new proposed technique performs better in dynamic behaviour tests, which shows its
    better potential for on-line dynamic NDT inspection which is required in many industrial
    applications. In addition to testing calibrated samples with different discontinuities, a study
    case using an aircraft lap joint sample from industry has further supported the statement
    regarding the potential of the new technique.

    Item Type: Thesis (Doctoral)
    Additional Information: EThOS Persistent ID uk.bl.ethos.399818
    Subjects: T Technology > T Technology (General)
    T Technology > TJ Mechanical engineering and machinery
    Schools: School of Computing and Engineering
    Depositing User: Sharon Beastall
    Date Deposited: 05 Feb 2010 07:58
    Last Modified: 28 Jul 2010 19:53
    URI: http://eprints.hud.ac.uk/id/eprint/6916

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