A REVISED FORM FOR THE JOHNSON–COOK STRENGTH MODEL

Strength models play a key role in the numerical simulation of impact events. A revised form of the Johnson–Cook strength model is proposed in this paper. The revised model treats the sudden strengthening that many ductile metals exhibit at strain rates greater than 10 4/s. Strain rates of this magnitude are generally considered to be beyond the capability of the split-Hopkinson pressure bar and so such abrupt strengthening behavior is often not observed and reported. A method to economically estimate all eight coefficients of the revised strength model using quasi-static tension data and Taylor impact test data reduced with a modified version of the EPIC finite element code is also described. Revised strength model coefficients were determined for: 7075-T6 aluminum, OFHC copper, wrought iron, and a high-strength steel (Astralloy-V ®). A good fit to the quasi-static tension data and Taylor impact test results was obtained for these four different metals. The behavior of the revised strength model at high strain rates also compared favorably with independent predictions from an analytical model calibrated with the Taylor impact data.