Sonic-IR, which is based on the detection of the temperature rise due to frictional heating at the defect faces under ultrasonic excitation, has an advantage in the detection of closed defects. However, in conventional sonic-IR method, to directly input an acoustic energy from ultrasonic transducer to the test area via ultrasonic horn, which may give scratches and deformation in the test object. In this study, we develop a new sonic-IR method using ultrasonic wave inputted through water, and practicability of the proposed method for the detection of fatigue crack is experimentally investigated.
