The Effects of Waveform in Residual Stress Relief by Vibration Technique

In this study, SS41 low carbon steel plate after welding was treated by vibration under resonance, sub-resonance and small wave, respectively. The objective of this research was compared with the effect of residual stress relaxation under different vibratory frequencies. The residual stress was determined by using the Hole-Drilling Strain Gage Method of ASTM standard E837. The residual stress was measured in the back side of bead after welding, the result showed that value of residual stress was positive and the highest stress was in the center of the weld. The residual stress was symmetrical from center of bead to edges of specimen. It was observed that stress distribution of the back side of bead was symmetrical. The residual stress was measured in the back side of bead after vibration. The results showed that the residual stress relaxation of resonance, sub-resonance and wavelet were reached to 28.4%, 34.3% and 39.3%, respectively. Therefore, the effect of residual stress relaxation was the best with wavelet frequency.

The wavelet was combined with main wave and high-frequency wave via waveform analysis. The main wave was the particular solution of non-homogeneous differential equation. The source of the main wave was provided by the vibration motor. High-frequency wave was the homogeneous solution of non-homogeneous differential equation. The source of high-frequency wave was the free vibration response. Comparing high-frequency wave of resonance, sub-resonance and wavelet showed that amplitude of high-frequency wave was the highest with wavelet frequency, and that of resonance frequency was the lowest. Thus, in the case of residual stress relaxation, the wavelet frequency had the best effect because of its highest amplitude of high-frequency wave. The result showed the higher the free vibration response, the better effect of residual stress relaxation.