Detection of Cracks in Metallic Objects by Arbitrary Scanning Direction Using a Double U-Shaped Orthogonal ACFM Probe

Abstract

Alternating current field measurement (ACFM) technique is developed for sizing cracks on structures. According to the theory of ACFM, the induced current field should be perpendicular to the crack in metallic objects. So conventional ACFM probes should scan the crack in a particular direction. In this paper, a double u-shaped orthogonal ACFM probe is present for cracks detection at arbitrary scanning direction using induced rotating current field. The finite element method (FEM) model is employed to analyze the rotating current field induced by the double u-shaped orthogonal ACFM probe. The experiments are carried out to test the crack on specimen at arbitrary scanning direction. Results show that the crack can be detected effectively at arbitrary scanning direction using the double u-shaped orthogonal ACFM probe.

Fig. 4 The rotating current field on the surface of specimen at different transient time, (a) t = 0, (b) t = 0.25 T, (c) t = 0.5 T, and (d) t = 0.75 T.