PURPOSE: To detect the internal stress distribution of a metallic plate material to be detected without contacting by measuring the degree of attenuation of a reflected wave of a transversal ultrasonic wave.
CONSTITUTION: A DC static magnetic field B is applied from a DC coil 9 to a beltlike plate 3 and in this state, a pulse current is supplied to a transmitting and receiving coil 11 from a high-frequency pulse generating circuit 14, generating an eddy current (i) in the surface of the beltlike plate 3 opposing to the transmitting and receiving coil 11. The mutual operation between the eddy current (i) and DC static magnetic field B causes the generation of varying strain in the external surface of the beltlike plate 3 and an ultrasonic wave in transversal wave mode propagates in the thickness direction of the beltlike plate 3. An ultrasonic wave reflected by the bottom surface returns to the surface of the beltlike plate. The resulting induced current is detected by said coil 11 to detect the internal stress distribution of the beltlike plate 3.
FUJIMOTO MINORU
KADOWAKI TAKASHI
TANAKA AKIHIRO
