MWM eddy current sensors for monitoring of crack initiation and growth during fatigue tests and in service

A new surface-mountable (conformable foil) eddy-current sensor called the Meandering Winding Magnetometer-Array (MWM-Array) has the capability to monitor crack initiation and growth in fatigue test coupons. Fatigue tests with the MWM-Array mounted on the surface inside a 6.4-mm hole in an Al 2024-T3 tension-tension fatigue specimen, demonstrated the capability to detect cracks with l < 50 mu m ( alpha < 25 mu m). This provides a new capability to monitor fatigue tests of coupons and components to determine the number of cycles to crack initiation and to study 'short crack' growth. Also, MWM conductivity measurements correlate with crack length, permitting crack length monitoring. Ongoing research is focused on depth monitoring as well. Numerous applications are under evaluation for permanently mounting MWM-Arrays in difficult-to-access locations on commercial and military aircraft.