Optional Strain-Rate Forms for the Johnson Cook Constitutive Model and the Role of the Parameter Epsilon_0

A brief review of the standard Johnson-Cook model is presented. Three optional strainrate forms are introduced and calibrated to laboratory data for A36 steel. Next a brief description of the LS-DYNA Version 971 implementation of the new strain-rate forms, within the existing viscoplastic formulation of the Johnson-Cook model, is presented. Finally, all four calibrated strain-rate forms are exercised in single element uniaxial stress test simulations, and the results are compared with the A36 steel effective stress versus effective strain data at three different strain rates. The comparison of the calibrated model response to the quasi-static A36 steel data is used to illustrate the role & of the Johnson-Cook parameter ε 0 .