Detecting flaws formed in surfaces of rotating members with ultrasonic waves

An apparatus for detecting a defect formed in a surface of a rotating member having a circular cross-section with the aid of an ultrasonic wave comprising:

• a focusing-type probe for emitting a focused ultrasonic wave toward the rotating member and receiving an ultrasonic wave reflected from the defect;
• first supporting means for supporting the rotating member rotatably about a center axis thereof;
• second supporting means for supporting said focusing-type probe with respect to the rotating member in such a manner that a center axis (a) of the probe is displaced from a normal axis (b) which passes through the center axis of the rotating member and extends parallel to said center axis of the probe by such a predetermined displacement about (x) that the ultrasonic wave is made incident upon the rotating member substantially at a critical angle of reflection, such that a portion of the ultrasonic wave is refracted thereby to propagate substantially along a surface of the rotating member as a surface wave, said probe being set at a distance from the surface of the rotating member which is substantially equal to the focal length of the ultrasonic wave emitted from the focusing-type probe, such that the ultrasonic wave projected from the probe is focused on the surface of the rotating member;
• and
• means for containing an ultrasonic wave propagating medium in which said probe, said first supporting means and said second supporting means are immersed.