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. J3 plays an important role in the instability inclination angle of ultrafine‐grained interstitial‐free (UFG IF) steel. A constitutive model is proposed to interpret the microscopic observation of the deformed specimens of UFG IF steel. The numerical and experimental results show that the effect of J3 on the UFG IF steel's adiabatic shear instability inclination angle deserves enough attention.