SEPARATION OF CONDUCTIVITY AND DISTANCE MEASUREMENTS FOR EDDY-CURRENTNONDESTRUCTIVE INSPECTION OF GRAPHITE COMPOSITE-MATERIALS

This article deals with the study of a process based on the principle of eddy current sensors for the nondestructive evaluation of graphite composite plates. This research has been carried out in the Laboratoir e d'Electricite Signaux et Robotique by the team working on data-colle cting sensors for robotics in collaboration with Aerospatiale. Eddy cu rrent sensors are characterized by their impedance, which varies when a conducting material is approached in their sensitive area. For a giv en sensor, the output signal depends directly on the electrical and ge ometrical properties of the object. In the case discussed here, the in teresting data are the distance between the sensor and the object, and its local conductivity. In order to invert the relationships between the sensor signal and the properties of the material, an external para metrical model has been developed. A scanning of the surface with a se nsor designed for good spatial resolution measurements gives two accur ate maps of the useful data.