Adiabatic Shear in annealed and shock-hardened iron and in quenched and tempered 4340 steel

Adiabatic shear localization is a catastrophic failure mechanism which can occur in ductile metals under high strain rate loading. This mechanism is d riven by a thermal instability process in which rapid temperature rise due to plastic work couples with thermal softening to cause uniform deformation to collapse into narrow bands of intense shear within which material ducti lity is exhausted. Adiabatic shear localization is studied in three ferrous metals: annealed Armco and as-received Remco iron, both of which are high purity alpha iron, shock-hardened Remco iron. and 4340 steel quenched and t empered to a range of hardness levels. Using a compressive split-Hopkinson bar, punching-shear experiments were performed at room and elevated initial temperatures at shear strain rates of up to 45 000 s(-1). Optical and scan ning electron microscopy was performed on the deformed shear specimens to d etermine the extent of shear localization and mode of failure, Experimental evidence showed that the tempered 4340 steels were susceptible to localiza tion through adiabatic shear banding; however, as-received and shock-harden ed Remco iron and annealed Armco iron were not. Finite element simulations of the experiments were performed utilizing a user material subroutine deve loped as part of this research. This constitutive routine incorporates two adiabatic shear failure criteria, namely (i) maximum shear stress with a mi nimum critical shear strain rate and (ii) flow localization. These criteria proved to be capable of predicting the onset of an instability; however, t he deformation which follows the instability was not predicted well,