Study On The Crystal Plasticity Numerical Simulation Of Ultrasonic Assisted Mesoscale Pure Titanium's Plastic Deformation

The micro-size parts' plastic deformation properties decreased because of the size effect.Ultrasonic vibration applied to deformed workpieces can reduce the flow stress and improve the formability.Therefore,ultrasonic vibration assisted deformation is been applied to the forming of micro-size parts.At present,many scholars have studied the mechanism of ultrasonic reduction of material flow stress by means of simulation,but few studies have considered the influence of twins on the HCP metal at which twin deformation is a kind of main deformation mechanism.In this paper,a crystal plastic finite element model with twinning was been established to simulate the upsetting behavior of meso scale pure titanium.In this paper,a crystal plastic finite element model of pure titanium microcolumns with twins was been constructed,and the plastic parameters of the related crystals were been determined by parameter fitting.The finite element model was been built by embedding the model program into the user subroutine-UMAT of ABAQUS.The crystal plasticity finite element method was been successfully applied to fit the relevant model parameters.By comparing the simulation results under the same deformation conditions with the experimental results,the reasonableness of the model was been proved.In order to introduce ultrasound into the finite element model,the vibration effect of ultrasonic was been simplified as a sinusoidal displacement curve,which was been applied to the surface of the die.In this paper,the deformation results at different ultrasonic frequencies and amplitudes were been compared with the experimental results obtained by pure titanium micro column upsetting using the self-designed ultrasonic assisted deformable device,further proving the rationality of the model.What's more,by comparing the simulation results of the crystal plastic finite element simulation with the isotropic finite element model,it was been verified that the crystal plasticity model could reflect the real deformation results more reasonably.Based on this,the effect of ultrasound on the volume fraction of pure titanium twins was been studied.It was been found that the volume fraction of twins decreased after ultrasonic application,the decrease of the volume fraction of deformation twins increases with the increase of ultrasonic amplitude.The mechanism of ultrasonic softening was been suggested by comparing with the results obtained from EBSD experiment.