Ultrasonic impact treatment (UIT) is currently used in several manufacturing processes. UIT is a process in which ultrasonic vibration is used to impact pins onto a metal surface. To clarify the mechanisms of deep compressive residual stress in UIT, the effects of the pin tip radius on residual stress distributions were analyzed by the dynamic explicit finite element method. The sonotrode vibration amplitude and frequency were 25 µm and 20 kHz, respectively. The pin velocity accelerated by the sonotrode was approximately 4.6 m·s⁻¹ at the first impact. The depth of the residual compressive stress remained nearly constant after the first impact for pins of various tip radii (1.5, 3, 8 and 12 mm). During the first 10 ms, eleven impacts occurred between the 8 mm tip radius pin and the metal surface. The pin velocities were highly dependent on the sonotrode velocity in the collision range from 4 to 16 m·s⁻¹. The depth of residual compressive stress increased with increasing impact number. After 10 ms, the depth of residual compressive stress was approximately 2.5 mm when using an 8 mm tip radius pin, and it increased with increasing tip radius.

This Paper was Originally Published in Japanese in J. JSTP 58 (2017) 35–40.