Recent Studies in Modeling for the A.C. Field Measurement Technique

  • D. H. Michael
  • R. Collins
Conference paper
Part of the Review of Progress in Quantitative Nondestructive Evaluation book series (RPQN, volume 6 A)

Abstract

Theoretical modeling studies associated with the a. c. field measurement technique have been a major feature of work at UCL for almost the last decade [1]. In that technique, the objective is to establish a spatially uniform current flow in the surface of a metal and to use this to interrogate a defect such as a surface-breaking crack by directing it broadside on to the crack and measuring the perturbations in the surface voltage distribution which it produces (Figure 1a). We have described the first major result of the theoretical studies as an unfolding theory. It shows that when the electrical skin depth δ is small compared with the defect size, the field problem posed by the interception of a uniform current flow by a surface-breaking crack is the plane potential problem shown in Figure 1c and d. The descriptive name was adopted because the problem domain is that formed by conceptually sectioning the material in the plane of the crack, as in figure 1b, and unfolding the crack plane about the surface edge BC to make it coplanar with the metal surface. This approach has been successfully used to solve the field problems associated with cracks of various forms, for example elliptical, circular arc, rectangular and triangular, and it has enabled us to incorporate the influence of crack aspect ratio on the readings of an a.c.f.m. instrument such as the Crack Microgauge [2], Earlier review papers [1,3] give numerous examples of the comparison between theory and experiment.

Keywords

Fatigue Rounded 

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References

  1. 1.
    R. Collins, W.D. Dover and D.H. Michael, The use of a. c. field measurements in non-destructive testing in. “Research techniques in non-destructive testing”, vol. VIII, R.S. Sharpe, ed., Academic Press, London (1985).Google Scholar
  2. 2.
    Inspectorate Unit Inspection Ltd, Sketty Hall, Swansea, UK.Google Scholar
  3. 3.
    R. Collins, D. Mirshekar-Syahkal and D.H. Michael, The mathematical analysis of electromagnetic fields around surface flaws in metals in “Review of progress in quantitative non-destructive evaluation”, Vol. 2B, D.O. Thompson and D.E. Chimenti, eds., Plenum, New York (1983).Google Scholar
  4. 4.
    D.H. Michael, R.T. Waechter and R. Collins, Proc. Roy. Soc., A 381, 139 (1982).CrossRefGoogle Scholar
  5. 5.
    W.D. Dover, G. Glinka and R. Collins, Automated crack detection and monitoring of crack shape evolution in tubular welded joints, in Proc. Int. Conf. on NDT in fitness for purpose assessment of welded constructions, Paper 11, The Welding Institute, London (1984).Google Scholar
  6. 6.
    In preparation.Google Scholar
  7. 7.
    J.D. Cockroft, Proc. Roy. Soc., A 122, 533 (1929).CrossRefGoogle Scholar
  8. 8.
    H.M. Shang, R. Haq, R. Collins and D.H. Michael, to be submitted for publication.Google Scholar
  9. 9.
    R. Collins, D. Mirshekar-Syahkal and D.H. Michael, Proc. Roy. Soc., A 393, 159 (1984)CrossRefGoogle Scholar
  10. 10.
    R. Collins, D.H. Michael, D. Mirshekar-Syahkal and H.G. Pinsent, Journal of NDE 5., (1985)Google Scholar

Copyright information

© Springer Science+Business Media New York 1987

Authors and Affiliations

  • D. H. Michael
    • 1
  • R. Collins
    • 1
  1. 1.London Centre for Marine TechnologyUniversity College LondonLondonUK

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