ADVANCED MAGNETO-OPTIC/EDDY CURRENT TECHNIQUES FOR DETECTION OF HIDDEN CORROSION UNDER AIRCRAFT SKIN

RECENTLY, NEW MAGNETO-OPTIC/EDDY CURRENT TECHNOLOGY HAS BEEN DEVELOPED FOR RAPID INSPECTION OF CRACKS INITIATING NEAR RIVETS IN ALUMINUM AIRCRAFT ALLOYS. THERE IS EVIDENCE THIS TECHNOLOGY CAN BE DEVELOPED FOR RAPID DETECTION AND IMAGING OF SUBSURFACE CRACKS AND CORROSION. UNCONVENTIONAL EDDY CURRENT INDUCTION METHODS EXCITE ELECTROMAGNETIC FIELDS IN THE PARTS, AND DETECTION IS ACCOMPLISHED WITH A MAGNETO-OPTIC SENSOR, PRODUCING DIRECT, REAL-TIME IMAGING OF DEFECTS. THE MAGNETO-OPTIC SENSOR RESPONS TO SMALL STATIC OR TIME VARYING MAGNETIC FIELDS NORMAL TO THE INSPECTION SURFACE. THESE FIELDS ARE PRODUCED WHEN CRACKS OR OTHER DEFECTS, INCLUDING CORRODED AREAS, INTERACT WITH THE INDUCED ELECTRIC CURRENTS. THEMAGNETOOPTIC SENSOR RESPONDS TO FREQUENCIES FROM 0 (DC) TO OVER 250 KHZ. THE LOWER FREQUENCIES (0 TO ABOUT 10 KHZ) SHOULD BE USEFUL FOR IMAGING AND DETECTION OF SUBSURFACE CRACKS AND CORROSION, AND THE HIGHER FREQUENCIES (10 KHZ TO OVER 200 KHZ) FOR DETECTION AND CHARACTERIZATION OF SURFACE CRACKS. DIRECT OBSERVATION OF THE MAGNETO-OPTIC SENSOR, USING POLARIZED LIGHT AND AN ANALYZER, REVEALS REAL-TIME IMAGES OF DEFECTS. THIS NEW TECHNOLOGY OFFERS THE ADVANTAGES OF VERY RAPID COVERAGE OF LARGE AREAS, HIGHER SENSITIVITY TO SMALL CRACKS, MORE DIRECT DETECTION AND CLASSIFICATION OF DEFECTS, AND SIMPLE, INEXPENSIVE RECORDING OF THE ENTIRE INSPECTION.