| 摘要 |
PURPOSE:To obtain an ultrasonic flaw detector which can detect flaws totally on line in the measurement of a depth of a planar defect in a plate material by arranging the apparatus made up of an array probe for transmission, an array probe for reception, an arithmetic processor for positions of defects from a received echo and the like. CONSTITUTION:Defect 14 in an object 11 to be inspected is parallel with the surface thereof as generated in a rolling process and array probes 1A and 1B are arranged in a symmetrical positional relationship. Ultrasonic beam 13 is propagated being refracted when entering the surface of the object 11 to be inspected. When an angle of incidence is set above a critical angle of a longitudinal wave, a lateral wave alone can be propagated through the object 11 to be inspected. As the lateral wave is slow almost half as much as sound velocity, a propagation time difference thereof due to a difference of a course doubles that of the longitudinal wave. As a wavelength thereof is shorter as compared with the sound velocity, the lateral wave is advantageous in the detection of fine defects as well. Thus, an electron focusing of the ultrasonic beam with the control of a delay time can improve resolutions and detection sensitivity with a less width of the beam. |
