RADIATION CHARACTERISTICS OF ULTRASONIC TIP ECHO AND ITS APPLICATION TO DETECT FATIGUE CRACK CLOSURE IN WELDING RESIDUAL STRESS FIELDS

摘要

Ultrasonic tip echo is scattered wave which radiates all direction from the sharp tip of reflection source nsuch as fatigue cracks. Tip echo has been utilized for sizing defects as so-called “tip echo method” and also nmay apply to identify fatigue cracks from other defects. In this study, radiation characteristics of the tip necho were experimentally examined. A linear phased array ultrasonic testing system was applied to send nand receive ultrasonic waves in various directions. The experimental results demonstrated the relationship nbetween incident wave directions and directivity of the tip echo. Besides, the tip echo method was applied nto a fatigue crack in a welded steel plate, and damping of echoes due to fatigue crack closure was indicated.