Eddy current sensors for nondestructive inspection of graphite composite materials

A system using eddy current sensors for nondestructive evaluation of graphite composite plates is described. The basic physical principle of measurement with this kind of sensor is reviewed. An analytical model of the relationships between the properties of the object approached by the sensitive area of the sensor and the induced variation of the signal is presented. In this case the interesting properties are the distance between the sensor and the target, and the latter's local conductivity. The inversion of this model to extract useful data from the sensor signal is discussed. The method is illustrated for a graphite composite plate on which a mechanical constraint was applied. The inspection process consists of scanning the sensor above the surface of the sample, and computing in each point values either of distance or conductivity. Both values, presented at successive stages of structure damage, show simultaneously the surface deformations and the internal defects in the sample.<
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