Shear localization in 4340 steel with different microstructure using thick wall cylinder method

Abstract

Initiation, self-organization of shear bands, and post-critical behavior of 4340 steel with initial low (2789 MPa) and high (5420 MPa) microhardnesses, but similar thermophysical properties, are studied using the explosively-driven Thick Wall Cylinder method and numerical simulations. In experiments, low hardness 4340 steel demonstrated the initiation of a pattern of shear bands at a global effective strain of about 0.53, which did not significantly change with an increase of global strain up to 0.8. High microhardness 4340 steel demonstrated extremely different post-critical behavior. At global strain 0.56, a few well-developed shear bands propagated through the sample with their transformation into a crack pattern at larger global strain 0.83. The propagation mechanism of shear bands in hardened 4340 steel is explained by the interfacial microcracking between inclusions and matrix. The Johnson-Cook material model with damage in numerical simulations correctly predicted the dramatic change of pattern of shear bands with the change in the initial steel properties at similar global strains. The pattern of shear bands was dependent on the number of initial material defects introduced by scaling of the yield strength of mesh elements.