The role of J₃ in the Orientation Analysis of the Adiabatic Shear Band of Ultrafine-Grained Interstitial-Free Steel

Within the framework of classical plastic theory, the instability inclination angle of metal is 45 ° under axial compression loading. However, microscopic observations by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show the ultrafine-grained (UFG) interstitial-free (IF) steel inclination angle of adiabatic shear instability is less than 45 °. Herein, a constitutive model that accounts for the effect of the third stress invariant is proposed based on the Johnson–Cook model to investigate the effect of J₃ on the adiabatic shear instability inclination angle of UFG IF steel. To give a clear and direct interpretation of this effect, the model is implemented in the commercial software ABAQUS/Explicit by user subroutine VUMAT. Then shear-compression specimens with different groove angles are used to investigate the influence of J₃ on the orientation of adiabatic shear band. Subsequently, dynamic tests of UFG IF steel shear-compression specimen with different groove angles are conducted through Split-Hopkinson Pressure Bar. The experimental results show that noncoaxial influence (the effect of J₃ or Lode angle) deserves enough attention in the orientation analysis of adiabatic shear instability of UFG IF steel.