Non-destructive evaluation distribution sensors based on magnetostrictive delay lines

In this paper, we present a non-destructive evaluation sensor able to perfo rm distribution measurements on metallic surfaces. The sensing principle is based on the magnetostrictive delay line (MDL) technique. The pulsed MDL e xcitation field generates eddy currents on the test surface, which are bala nced when no cracks are present. In case of cracks, these eddy currents are summed up around the inhomogeneity, thus causing microstrain generation in the region of the MDL close to the crack. The amplitude and time delay of the detected pulsed voltage signals corresponding to those additional micro strains caused by the eddy currents, are the indication of the size and the position of the defect on the test surface. In this paper, we present the sensing principle as well as the first results in such kind of measurements . (C) 2001 Elsevier Science B.V. All rights reserved.