An enhanced Johnson–Cook strength model for splitting strain rate and temperature effects on lower yield stress and plastic flow

Abstract This paper introduces a new ‘strength model’, named Split Johnson–Cook (SJC). The model is a generalization of classical Johnson–Cook (JC) and provides a much improved coherence for the plastic material description. Specifically, the new model tackles the issue that the effects of equivalent plastic strain rate and temperature shall not be taken as equal for each equivalent plastic strain, avoiding then heavy modeling errors on the lower yield stress and on the subsequent plastic flow. The salient features of the original JC model are shortly reviewed first, paying specific attention to possible modeling incoherencies. Two main shortcoming issues are framed and discussed. Further, a review on several modifications of the JC model from the literature is outlined. Then, the new SJC model is introduced in such a framework and thoroughly described. A comprehensive discussion on its calibration strategies follows, by developing three alternative calibration approaches. The new model is then applied to the material description of three real material cases (a structural steel, a commercially pure metal and a stainless steel), by considering literature sets of hardening functions recorded at different equivalent plastic strain rates and temperatures. SJC predicted trends are checked against experimental data, for each calibration strategy, by evaluating the material prediction on both lower yield stress and plastic flow. Obtained results are also compared to those provided by plain JC. The SJC model shows the capability to remarkably improve the material description, as compared to plain JC. Moreover, the fact of presenting a form very similar to that of the original JC model allows to possibly reusing some of the JC material parameters, which may be already known from available calibrations. Also, the SJC model keeps the same computational appeal of the original JC model and need of experimental data toward calibration, while heaviness of calibration and computational weight remain almost unchanged.