Modification of the Johnson-Cook constitutive model for 34CrNi3MoA alloy steel based on the temperature-strain rate coupling effect

Abstract

This work examines the high-rate compression response of 34CrNi3MoA alloy steel by means of SHPB tests carried out at 25 °C, 200 °C, 400 °C and 600 °C, with strain rates ranging from 1000 to 4600 s⁻¹. The experimental curves indicate rate strengthening, thermal softening and a local stress increase related to dynamic strain aging in a specific temperature rate interval. When the conventional Johnson-Cook model was calibrated with the same data set, the average relative error reached 20.63%, showing that the separable strain, rate and temperature terms were insufficient for this material. To improve the description, the model was revised by introducing a rate-dependent thermal-softening exponent, a two dimensional Gaussian function for the dynamic-strain-aging peak and a hardening coefficient coupled with both temperature and strain rate. The revised model reduced the average relative error to 2.88% and gave a closer representation of the measured curves within the tested range. The proposed equation is therefore recommended as an interpolation model for 1000-4600 s⁻¹ and 25-600 °C; application beyond this domain still requires further calibration and uncertainty evaluation.