HIGH STRAIN RATE SHEAR EVALUATION AND CHARACTERIZATION OF AISI D2 TOOL STEEL IN ITS HARDENED STATE

Abstract

High strain rate mechanical testing on fully hardened AISI D2 tool steel (at 62 HRc) was performed utilizing the Compressive Split Hopkinson Bar technique (CSHB) incorporating a punching shear strain state. The high strain rate conditions were comparable to those encountered in machining processes, with shear strain rates on the order of 5 × 104 s−1 and shear strains in excess of unity (100% mm/mm). The tests were performed at various initial temperatures ranging from 296–873 K to investigate the flow stress behavior of the hardened tool steel as a function of temperature. The high strain rate experimental shear stress-strain data was used to fit the flow stress by; i) an empirically based constitutive law in the form proposed by Johnson and Cook; as well as, (ii) a physically based constitutive law proposed by Zerilli and Armstrong which accounts for strain, strain rate, and temperature dependence of flow stress. The data incorporated the adiabatic temperature rise in the shear zone and was used in the constitutive law modeling. The deformed microstructure was investigated using optical and scanning electron microscopy to determine the extent of the shear localization zone and the final fracture mode.