Impact effect of superimposed ultrasonic vibration on material characteristics in compression tests

Abstract Conventional ultrasonic-assisted forming in macro scale has been studied widely for decades. However, ultrasonic dynamic impact effect, which only occurs in micro-scale, has never been studied thoroughly. The purpose of this study is to investigate and identify the influencing parameters of amplitude and vibration time for the ultrasonic-induced stress reduction considering dynamic impact effect. As the first step for the purpose, commercially pure aluminum 1100 with specimen size of 2 mm in diameter and height were selected for ultrasonic-assisted compression tests with varying amplitude and press speed. Ultrasonic-induced stress reduction was evaluated and the contour shape of deformed specimens was compared to obtain the effect of ultrasonic vibration on material deformation. The results showed that, ultrasonic dynamic impact effect was the dominating mechanism for stress reduction in compression condition, the stress reduction which caused was nearly 5 times of the sum by stress superposition and acoustic softening. The ratio of amplitude to specimen height is identified as an influencing index for occurrence of ultrasonic dynamic impact effect, for which the critical value equals to half of yield strain. The findings showed promising prospect of ultrasonic vibration in micro-forming, which helped to provide a basis to understand the underlying mechanism of ultrasonic-assisted micro-forming and design the process in next step.