A NUMERICAL STUDY OF ADIABATIC SHEAR BANDING IN MILD-STEEL BY DISLOCATION MECHANICS BASED CONSTITUTIVE RELATIONS

This paper addresses instability and localization of plastic shear at different imposed rates. A wide range of the nominal strain rates in s hear has been studied numerically, from 50 s(-1) to 10(5) s(-1). A, la yer with a small geometrical defect is assumed, which dimensions are e xactly the same as in the double shear specimen used in impact loading (Klepaczko, 1994). A one-dimensional model for simple shear deformati on was applied together with the complete constitutive relations based on structural evolution and dislocation kinetics, The constitutive mo delling based on dislocation dynamics is limited to BCC structures, mo re exactly to mild carbon steels. The complete thermal coupling of pla stic deformation was taken into account with exact Debye model for the specific heat, as well the thermal conductivity was accounted for in the numerical analyses. All material constants in the constitutive rel ations have been found and numerical analyses have been performed for XC18 steel (similar to 1018 steel of AISI). ?The complete analysis of this numerical study is given elsewhere (Rezaig, 1994). It has been fo und that the critical nominal strain rate exists at which the formatio n of the adiabatic shear band (ASB) is the easiest (similar to 5 . 10( 3) s(-1) for the steel studied). At very high nominal strain rates (si milar to 10(5) s(-1)) the increase of temperature inside the band was found to be close to the melting point. Within the range of the nomina l strain rates of the order of 10(3) s(-1), the thickness of the ASB i s the smallest.