Molecular dynamics study of acoustic softening effect in ultrasonic vibration assisted tension of monocrystalline/polycrystalline coppers

Abstract

Ultrasonic vibration assisted metal forming is a promising technology, but the microscopic mechanism of the ultrasonic effect on metal deformation has not been fully understood yet. In this paper, by molecular dynamics simulation, the microscopic mechanism behind the acoustic softening effect of ultrasonic vibration was studied. The stress superposition and acoustic softening can be simulated simultaneously by molecular dynamics method, and the stress–strain response of the polycrystalline copper simulations agrees well with the experimental results. Based on the analysis of atomic kinetic energy and dislocation density, it is found that ultrasonic vibration increases the atomic kinetic energy and promotes the generation, multiplication, motion, and annihilation of dislocations in the plastic deformation process, resulting in a reduction of dislocation tangles and pile-ups. Therefore, the hindrance to crystal sliding is significantly decreased, which promotes the plastic deformation accompanied by a macroscopic reduction in flow stress of copper. As for different ultrasonic parameters, the influence laws of ultrasonic amplitude and frequency on the deformation behaviors of coppers are different. These findings play an essential role in revealing the mechanism of ultrasonic vibration assisted plastic forming.