Investigation on Material Deformation Characteristics of Ultrasound-assisted Microcompression with Dynamic Force Sensing Technology

摘要

Ultrasonic vibration is a promising assistant technology to improve the microforming processes, for example, decreasing friction, enhancing surface finishing, and reducing forming load/stress. However, the mechanism behind the forming stress reduction due to ultrasonic vibration, so-called acoustic softening, is still not totally understood, because in most previous research studies, a simplified force sensing technology, which could not measure the real dynamic ultrasonic force during deformation, was used. In order to solve this issue, an ultrasound-assisted microcompression test system with a die-embedded dynamic force sensor was developed for studying the evolution of acoustic softening. With this system, the stress reduction by acoustic softening can be obtained by separating the stress reduction by stress superposition, which is just an apparent stress reduction due to the averaging of the dynamic oscillatory stress. Then, the stress reduction by stress superposition is verified using a theoretical model, confirming the reliability of the test system. Thus, the evolution of material deformation characteristics can be analyzed. By comparing the stress superposition to acoustic softening, it is found that stress superposition is greater than acoustic softening at the beginning of deformation, especially with a smaller ultrasonic amplitude. Even as the ratio of stress superposition to acoustic softening gradually decreases to some extent with increasing strain, stress superposition still accounts for nearly half of the total stress reduction. The results emphasize the importance of the dynamic force sensing technology in ultrasound-assisted microforming and provide some instructive understanding of the mechanism of acoustic softening.