An investigation of stress condition in vibration-assisted burnishing

Abstract

Burnishing has been proved to be a faster, lower-cost, and more effective strengthening process to improve surface integrity especially for alloy components when compared with heat treatment. It has been suggested that smaller static force is necessary to the required deformation when vibration excitation is superimposed to the static force, and this kind of material softening phenomenon resulting from external excited vibration is called acoustoplastic effect. This work is to investigate the influence of vibration excitation on the material under deformation in terms of stress condition. A 3D finite element model has been developed and validated by the experimental data. The effect of vibration frequency of 0–28 kHz on the total contact force as well as the distribution of residual stress and plastic strain fields was comprehensively analyzed. The vibrations at different frequencies studied in this work caused the increase of the maximum contact force. Overall, vibrations at 0 kHz, 0.1 kHz, 1.3 kHz, and 14 kHz led to the increases of the maximum residual stress and equivalent plastic strain while not exerting pronounced effect on the distribution of stress and strain fields of treated samples. However, in case of a very high frequency vibration at 28 kHz, pulse hammering contact force produced between the rolling ball and being treated surface, resulting in a significant change of the distribution of stress and strain fields. The observations at high vibration frequency can be interpreted as that pulse hammering contact force produced at some high frequency coupled with other process parameters caused the formation and continuous propagation of dynamic oscillatory stress wave traveling long distance inside the material.