Ultrasonic assisted incremental sheet forming: Constitutive modeling and deformation analysis

•A hybrid constitutive model is developed to describe the stress-strain behaviors under ultrasonic vibration.•Finite element models are developed and verified for the ultrasonic-assisted ISF process.•The affecting mechanism of ultrasonic vibration on material deformation behavior is revealed.•Ultrasonic-actuated dynamic recovery is observed through microstructure examination. Ultrasonic vibration has been applied in the incremental sheet forming process and shows the potential to reduce the forming force and increase the formability, but the constitutive behavior and deformation behaviors of material under the high-frequency vibration are still not completely explained. In the present work, a hybrid constitutive model which combines the phenomenological, thermal activation and dislocation annihilation models is established and experimentally calibrated. Then, a finite element model is developed for the ultrasonic-assisted incremental sheet forming (UISF), in which the hybrid constitutive model and a user defined subroutine were incorporated to describe the ultrasonic effect and to simulate the high-frequency vibration, respectively. Compared with the experimental forming force, the FE analysis with the hybrid constitutive model shows good predictability with errors less than 10 %. Based on the simulation results, the improvement of formability was observed and the material deformation behavior during ultrasonic-assisted incremental sheet forming was analyzed in detail. Moreover, the material microstructural features were analyzed through Electron Back Scatter Diffraction (EBSD). The occurrence of relative larger grains and the increase of low angle grain boundaries (LAGBs) indicates the occurrence of ultrasonic-actuated dynamic recovery of the material.