A contactless self-scanning electro-elastic nondestructive testing technique is described for determining in real time the presence, location, number and size of defects present on the surface of a material under test. In one embodiment the apparatus includes means for inducing eddy currents or current flow in the surface of the conductive material. A magnetostrictive delay line is disposed parallel to the direction of current flow and equidistant and in fixed spatial relation with the surface. The presence of a crack or defect in the surface proximate to the delay line creates transverse eddy currents or transverse currents in the material which interact locally with the magnetostrictive delay line to induce elastic waves in the delay line. The elastic waves are generated in the delay line only at locations corresponding to the edges of the defects. An ultrasonic sensor coupled to the delay line is used to detect the elastic waves travelling in the delay line. The location of a crack or fissure may be determined based on the time of arrival of the elastic waves at the sensor. The self-scanning line electro-elastic probe is not susceptible to the presence of elastic waves propagating in the material under test. The invention is applicable for inspection of flat and curved surfaces.PPAnother elastic wave transmitting medium may be employed in place of the magnetostrictive delay line given appropriate excitation means. Additionally, the delay line may be fabricated as a two-dimensional sheet with ultrasonic sensors disposed at selected locations on the sheet to achieve rapid inspection of an area for defects, the location of defects being determinable based upon the time of arrival of induced elastic waves at respective sensors.
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