2017 年 58 巻 672 号 p. 35-40
Ultrasonic impact treatment （UIT） is recently being used in several manufacturing processes. UIT is a process in which ultrasonic vibration is used to throw pins onto a metal surface. In order to clarify the mechanisms of deep compressive residual stress in UIT, the effects of the pin tip radius on residual stress distributions are analyzed by the dynamic explicit finite element method. The sonotrode vibration amplitude is 25 μm and its frequency is 20 kHz. The pin velocity accelerated by the sonotrode is about 4. 6 m·s-1 at the first impact. The depth of residual compressive stress stays nearly constant for pins of various tip radius （1. 5, 3, 8, 12mm） after the first impact. During 10 ms, eleven impacts occur between the pin and the metal surface in the case of using an 8 mm-tip-radius pin. The pin velocities depend a great deal on the sonotrode velocity in the collision range from 4 m·s-1 to 16 m·s-1. The depth of residual compressive stress increases with increasing impact number. After 10 ms, the depth of residual compressive stress is about 2. 5 mm when using an 8 mm-tip-radius pin and it increases with increasing tip radius.