Study of the dipole model of a crack

Minkov, D.; Shoji, T.; Lee, J.
May 2000
AIP Conference Proceedings;2000, Vol. 509 Issue 1, p521
Academic Journal
The dipole model of a crack (DMC) is applied for a first time assuming that the distribution of the surface density of magnetic charge at the crack walls m along the depth of a surface crack is not constant, but is described by a second order polynomial. New analytical expression is derived for the z-component of the intensity of the leakage magnetic field (ZILMF) in this case. DMC inversion is performed using Hall sensor measurements of ZILMF by varying the coefficients of the second order polynomial which leads to determining the depth distribution of m. Additional inversions are performed assuming correspondingly constant and linear depth distribution of m and the results and the accuracies of the different inversions are compared. It is shown that m is significantly larger at the tip of the crack with respect to its mouth which indicates that the depth distribution of m should not be considered to be constant. Instead, the distribution of the surface density of magnetic charge at the crack walls m along the depth of the crack can be represented by a polynomial of first or second order, and the distribution of the corresponding ZILMF is described by the new analytical expression. These developments might make DMC inversions a viable alternative of Eddy-current inversions. © 2000 American Institute of Physics.


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