NDTnet 1998 Aug, Vol.3 No.8

Abstract

Eddy-current non-destructive evaluation is widely used in the aerospace and nuclear power industries for the detection and characterization of defects in metal components. The ability to predict the probe response to various types of defect is highly valuable since it enables the influence of particular parameters to be studied without recourse to costly and time consuming experiments. The solution of forward problems is also essential in the process of inverting experimental data.

Thin-skin regime
This paper compares experimental datafor aluminium and steel specimens withtwo methods of solving the forward problem in the thin-skin regime (fig 1).In this regime, the electromagnetic skin depth is small compared with the depth of the crack. Such conditions are common in tests on steels and sometimes on aluminium.

Two modelling approaches
The first approach is a 3D Finite Element / Boundary Integral Element method (TRIFOU) which may be applied to a wide range of problems in the fields of magnetostatics, microwaves and time-harmonic as well as transient eddy-currents (1). The second approach is specialized for the treatment of surface cracks in the thin-skin regime (2). The problem is formulated in terms of a single scalar potential which obeys the Laplace equation on the crack surface and thin-skin boundary conditions at the crack perimeter.
These models accurately predict the probe response to cracks in the thin-skin regime and therefore can be used in probe design. The specialized method is less computationally intensive than the general purpose code, making it more promising for use in inversion.

fig 1 : Scan along the mouth of a rectangular slot in aluminium.

1. Gros, PO, Rew. Prog. Quantitative Nondestr. Eval. 1997: 257-261.
2. Harfield, N, Bowler, JR, J. Appl. Phys. 1997: publication scheduled 15th October.

Abstract Source:
Book of Abstracts, 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN: 87-986898-0-00

Full-Text Source:
Proceedings of the 7th European Conference on Non-Destructive Testing, 26-29 May 1998, ISBN:

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