The inversion of surface potential measurements to determine crack size and shape

Connolly, Melissa; Michael, D. H.; Collins, R.

doi:10.1063/1.341629

Cited by 21 publications

(6 citation statements)

References 3 publications

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“…The together use of physical measurement and filed modelling allows the exclusion of calibration procedure, which minimises possible errors occurring during calibration activities applied by other NTD methods [30][31][32]35]. Inverse problems associated with crack profile determination have been solved with numerical iterative procedures [54]. With respect to small crack sizing ability, it has been reported that ACPD was preferred in monitoring long shallow surface cracks but lost accuracy in cases of deep surface cracks that could be accurately predicted by ACFM [30].…”

Section: Alternating Current Field Measurementmentioning

confidence: 99%

Potential difference methods for measuring crack growth: A review

Rouse

Hyde

2020

International Journal of Fatigue

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Non-destructive testing techniques are widely applied in industry for the evaluation of quantities of interest without inflicting additional damage accumulation. Crack detection and monitoring is a prime example of where non-destructive testing is valuable. Among the variety of non-destructive testing techniques, the direct current and alternating current potential difference methods, which are based on the principle that an electrical potential field around a conductive specimen is disturbed by the presence of geometric irregularities (or "features"), have received a great deal of attention in the literature. This is mainly due to the high levels of accuracy associated with these techniques and good estimations of crack initiation and propagation having been achieved.A critical review of the evolution and applications of potential difference methods is presented in this paper. Potential difference methods are capable of providing accurate and continuous measurements with simple installation and exclude the requirement of visual access under harsh service conditions. Alternating current potential difference methods require lower current input than direct current equivalents and hence provide higher sensitivity and offer better noise rejection but are vulnerable to capacitance effects and are more expensive. Calibration curves can be determined analytically, numerically, or by direct or analogue experimental techniques with each method offering strengths and limitations. Application of these should be determined in accordance with the specific scenario. The performance of electric probes (of voltage measurements and current injection) on topand side-face of C(T) and SEN(B) specimens are reviewed in detail as case examples. Specific guidance in normalising measurements and eliminating errors from thermoelectric effects can be implemented in order to improve the accuracy of PD methods. Abundant results have been obtained by applying PD methods in monitoring cracks geometries under aggressive conditions such as corrosion, high temperature, creep and cycled loading.

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Section: Alternating Current Field Measurementmentioning

confidence: 99%

Potential difference methods for measuring crack growth: A review

Rouse

Hyde

2020

International Journal of Fatigue

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“…Quantitative measurement of cracks and defects based on the application of inverse analysis has been made by a lot of researchers using D.C. or A.C. electric potential method [1][2][3][4][5], ultrasonic method [6,7], elastodynamic method [8] and strain measurement [9], etc. Recently, crack detection has been regarded as one of the inverse problems.…”

Section: Introductionmentioning

confidence: 99%

Efficient and accurate determination of mode I type 3-D surface crack by measuring strain around the crack on the idea of the body force method

et al. 1995

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In this study, the location and the size of a three-dimensional semi-elliptical surface crack in a semiinfinite body are detected from data of strains measured around a region of the crack. Also the loading stress at infinity is treated as an unknown parameter. The crack location, size and the loading stress are determined through the condition which minimizes the square sum of residuals between measured strain distributions and computed ones for an assumed crack. The body force method is used to calculate the strain field around the crack. In order to obtain the solution with short CPU time, the crack is represented by a set of force doublets, and the database of the magnitudes of force doublets for various aspect ratios of the crack is utilized. The method of gradient search is employed to find out an optimal set of parameters. The fact that the strain field around the surface crack is mainly dominated by the crack area is utilized in detecting the crack. Several inversion schemes are examined to obtain accurate results. Numerical simulations are carded out and the results show that crack location, shape and loading stress are determined efficiently with good accuracy.

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“…In practice, this latter assumption is not particularly restrictive, as it is possible to locate the crack tips by considering the variation in the voltage signal as a probe moves along the length of the crack. In a concurrent study (Connolly et 1988), this problem has also been considered by using an iterative technique. Their method requires an initial guess of the crack shape to be made using the one-dimensional estimate.…”

Section: Introductionmentioning

confidence: 99%

Characterization of surface-breaking cracks in metal sheets by using AC electric fields

McIver

1989

Proc. R. Soc. Lond. A

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A surface-breaking crack in a metal sheet may be detected by passing an alternating current through the sheet and making measurements of the potential difference on the sheet’s surface. The distribution of potential on the metal surface depends on the exact geometry of the crack and the aim of this work is to predict the shape and size of a surface-breaking crack from the potential distribution. The theoretical model is formulated using the potential and streamfunction as the independent variables and the shape of the lower edge of the crack is determined from the solution of a Fredholm integral equation of the first kind. This is solved using a minimization technique which suppresses the instability of the equation. The method is tested using theoretical distributions of potential from known crack shapes and very good agreement is obtained in each case.

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The inversion of surface potential measurements to determine crack size and shape

Cited by 21 publications

References 3 publications

Potential difference methods for measuring crack growth: A review

Potential difference methods for measuring crack growth: A review

Efficient and accurate determination of mode I type 3-D surface crack by measuring strain around the crack on the idea of the body force method

Characterization of surface-breaking cracks in metal sheets by using AC electric fields

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