MWM eddy-current arrays for crack initiation and growth monitoring

Permanently mountable and scanning MWM® (Meandering Winding Magnetometer) eddy-current arrays provide an effective means of monitoring fatigue in laboratory tests of specimens and test articles as well as in service on structural components, e.g., aircraft high-strength components, heavy machinery components, and bridge members. The MWM-Arrays can detect and monitor early stage fatigue damage and cracks by measuring electrical conductivity or, in the case of ferromagnetic materials, magnetic permeability. Preliminary results of fatigue tests with linear MWM-Arrays, mounted on a shot peened surface or on a shot peened and cadmium plated surface in the semi-cylindrical gage region of custom-designed high-strength fatigue specimen, are presented and discussed. The results indicate that both permanently mounted MWM-Arrays and scanning MWM-Arrays can detect fatigue damage in steels well before formation of cracks as verified by post-test scanning electron microscopy.