Acoustic softening and residual hardening in aluminum: Modeling and experiments

► Acoustic plasticity was modeled based on the crystal plasticity theory. ► Vibration energy results in temporary softening and residual hardening. ► The stress decrease during the vibration is proportional to the vibration amplitude. ► The acoustic residual hardening is affected by the vibration duration and magnitude. ► The acoustic residual hardening is time-dependent rather than strain-dependent. It is known that high-frequency vibration affects metal plasticity during metal forming and bonding operations. Metal plasticity is significantly affected by the acoustic field leading to acoustic softening and acoustic residual hardening. In this study, a modeling framework for the acoustic plasticity was proposed based on the crystal plasticity theory. The acoustic softening and acoustic residual hardening effects were modeled based on the thermal activation theory and dislocation evolution theory, respectively. To validate the developed model, vibration-assisted upsetting tests were conducted using pure aluminum specimens. Results showed that the stress decrease due to the acoustic softening was proportional to the vibration amplitude. Moreover, the acoustic residual hardening effect was influenced by the vibration amplitude and duration. The unified acoustic plasticity model accurately captured the acoustic softening and hardening in aluminum. The predicted stress–strain response of the vibration-assisted upsetting agreed well with the experimental results. The findings confirmed the significant effects of high-frequency vibration on metal plasticity and provided a basis to understand the underlying mechanisms of vibration-assisted forming.