Development of ultrasonic vibration assisted uniaxial tension device and utilization in evaluation of micro tension deformation behavior of copper foil

ABSTRACT

For lots of advantages e.g. softening effect, ultrasonic vibration was widely used in industry. However, investigations were mostly focused on acoustic softening effect of flow stress, and other effects were seldom studied, which were very important for micro sheet forming. In this paper, a vibrator with sandwich structure was developed using piezoelectric ceramics PZT-8 as the ultrasonic transducer. A groove structure was designed at the end of vibrator to clamp the copper foil in the tension test. Dimensions of vibrator were determined by calculation and FE-simulation. The longitudinal vibration frequency and amplitude of manufactured vibrator were measured by laser vibrometer Polytec OFV-5000 as 35.21 kHz and 0.735 μm, respectively. With the developed device, a serial of tension tests were carried out using copper foil with different grain sizes. The results show that yield stress decreases when ultrasonic vibration is applied, which can be attributed to the acoustic softening effect. It is interesting to find that hardening index increases with ultrasonic vibration, and this means that limit formability can be improved in bulging forming, etc. Extensibility becomes smaller for the transverse vibration and fatigue damage. These findings are very helpful for understanding effect of ultrasonic vibration in micro sheet forming processes.

KEYWORDS:

• Micro tension deformation
• ultrasonic vibration
• yield stress
• hardening index
• limit formability
• extensibility

Funding

Authors gratefully acknowledge the financial support of the National Science Foundation of China (No. 51375113, No. 51635005) and the Fundamental Research Funds for the Central Universities (No. HIT.BRETIII.201404).