Rotating Field EC-GMR Sensor for Crack Detection at Fastener Site in Layered Structures

TLDR

Eddy‑current techniques have been used to inspect embedded cracks under fastener heads in riveted structures, yet they struggle to detect cracks not perpendicular to current flow and are hampered by the strong signal from high‑permeability steel fasteners. This study designs a rotating electromagnetic field that electrically rotates the applied magnetic fields and eddy currents to provide uniform sensitivity for crack detection in all radial directions around fastener sites. Giant‑magnetoresistive sensors image the normal component of the rotating field, enabling detection of cracks of various orientations on both aluminum and ferromagnetic fastener sites. Numerical modeling and experimental validation confirm the effectiveness of the rotating‑field EC‑GMR sensor for crack detection at fastener sites.

Abstract

Eddy current-based techniques have been investigated for the inspection of embedded cracks under fastener heads in riveted structures. However, these techniques are limited in their ability to detect cracks that are not perpendicular to induced current flows. Further, the presence of a steel fastener of high permeability produces a strong signal that masks relatively smaller indication from a crack. In this paper, a rotating electromagnetic field is designed to rotate the applied magnetic fields and related eddy currents electrically so that the sensor shows uniform sensitivity in detecting cracks in all radial directions around fastener sites. Giant magnetoresistive sensors are employed to image the normal component of this rotating field, to detect different crack orientations at aluminum and ferromagnetic fastener sites. Numerical model-based studies and experimental validation are presented.