Tailoring of residual stress by ultrasonic vibration-assisted abrasive peening in liquid cavitation of metallic alloys

The present study proposes a novel method of ultrasonic vibration assisted-abrasive peening for the enhancement of residual stress on the surface of metals and their alloys. The system employs a vibrating sonotrode that drives the formation and collapse of bubbles within a fluid medium. The imploding bubbles produce pressure waves which transfer momentum to the abrasives which are uniformly distributed in the fluid medium. The abrasives bombard a targeted surface along with intense pressure waves. This induces compressive residual stress through local plastic deformation in a short period. The capability of the ultrasonic-assisted abrasive peening setup is analysed in terms of residual stress by altering the abrasive concentration, peening time, and stand-of-distance between the bottom of the sonotrode and the exposed surface to be treated. The process is able to induce significant residual stress at around 67 % of yield strength for hard material Ti–6Al–4V and more than 80 % of yield strength for ductile materials, Al-6061 and OFHC-Cu. A numerical method coupled with a finite element model is employed to predict the dynamics of the process from cavitation of the bubble to the plastic deformation of the work material. At first, the model estimates the magnitudes of high-pressure waves at the bubble implosion near the solid surface, micro-jet velocity, and abrasive velocity. This information is then fed to Abaqus for numerical modelling of the deformation of work material. The impact of high-speed abrasives in the range of 100 m/s, pressure waves and microjets at the material surface are simulated through the FE model. The simulated results are verified with experimental findings in terms of surface residual stress for different materials, deviating within 10 %.