Investigations on mechanical properties of copper foil under ultrasonic vibration considering size effect

Plasticity of materials is significantly affected under the excitation of acoustic field leading to softening effect (Blaha effect). In microforming field, ultrasonic vibration is playing an important role when the geometry size of metal part is scaling down. In this study, a kind of ultrasonic vibration assisted uniaxial tension device was developed to investigate the mechanical properties of the copper foil T2, and its mechanical behavior under acoustic field considering size effect. Ultrasonic transducer with a groove structure was designed at the end of ultrasonic horn to clamp the specimen. The longitudinal vibration frequency of the ultrasonic transducer is 21.1 kHz and the vibration amplitude is in an adjustable range of 5-15 μm. Uniaxial tension tests were carried out at different tension speeds using the specimens with different sizes and thicknesses in the case with and without ultrasonic vibration. The results show that the flow stress decreases when the specimen geometry size is scaling down in both the cases with and without ultrasonic vibration. A decrease-ratio is introduced to describe the effect of ultrasonic vibration on different geometry size. It is found that the smaller the specimen geometry size is, the more significant the softening effect will be. The findings provide a reference to the study of size effect in microforming and the application of ultrasonic vibration.