Improvement in the detection of subsurface fatigue cracks under airframe fasteners using improved rotating giant magneto-resistance magnetometer head

Improved Giant Magneto-Resistance Magnetometers(IGMRM) offer many advantages for the detection of subsurface cracks. This paper presents new opportunities for the detection of fatigue cracks close to fasteners or rivets with an improved rotating head. The latter was developed around an IGMRM and a well designed electromagnetic flux focuser. The capabilities of the system for the first to the third aluminium layers (3 to 4 mm-thick each) flaw detection will be highlighted. Experimental Electro Discharge Machined (EDM) crack sizes under fasteners are several millimetres long and about 100 m wide. Currently, results show the ability of the system to detect very easily a 7 mm-long machined crack near a rivet under 6 mm of aluminium. The use of IGMRM as a field detector, for improved low-frequency response and sensitivity of the device, is discussed. A 2D finite element modelling result of electromagnetic field distribution for this newly designed rotating probe is presented. Also, the complete system configuration is described.