Influence of Ultrasonic Vibration on Metallic Friction

Abstract

The influence of vibrations on the internal friction of metals has been investigated by tensile and bending tests with superimposed ultrasonic vibrations at 20 kHz. In contrast with previously published work, these experiments have shown that the internal friction is not influenced because the yield strength of the sample is reduced by an amount which just equals the induced acoustic stress amplitude. Therefore, the effect comes from the super position of stresses. On the other hand, the boundary friction can be reduced by ultrasonic vibrations. This effect depends on the vibration direction in relation to the moving direction as well as on the vibration speed in relation to the moving speed. If the moving speed equals or surpasses the vibration speed, no reduction of boundary friction can be obtained. As an example of technical application wire drawing experiments with superimposed ultrasonic vibrations have been carried out. In most cases, the drawing force is reduced approximately by the amount of the acoustic stress amplitude if the drawing speed is low and if a certain resonance condition is checked.

An alternative explanation of forming force reduction for forming process submitted to vibration: Influence of the waveform in the viscoplastic domain

“…Secondly, another effect known as surface effect could take place. Indeed, it is known that the effective coefficient of friction drops with periodic reduction of contact areas and/or periodic change in direction of friction force vector as studied by Lehfeldt (1969). This results in a 'dynamic' lubrication.…”