Experimental Study on Strain Hardening and Strain Rate Effect of Q420 Steel

Uni-axial tensile tests of Q420 steel at different strain rates (0.001-288 s-1) were carried out to study strain rate effect on mechanical properties by INSTRON and Zwick/Roell HTM5020 testing machine. The experimental results show that Q420 steel is sensitive to strain rates, with strain hardening characteristic changing along strain rates. Finite element (FE) modeling of these tensile tests is developed to reversely extrapolate the true stress-strain relationship of Q420 steel beyond necking, using LS-DYNA of ANSYS. The simulation results show that the true stress-strain relationships of Q420 steel transform from power-law Ludwik model to exponential Voce model with the increasing strain rate. To get a fine dynamic constitutive model, a modified H/V-R model is established by introducing a new strain rate sensitivity function into the H/V-R constitutive model, where Wagoner rate law is replaced by the dynamic increase factor of the Cowper-Symonds model. The results show that the modified H/V-R model fits the experimental data well and captures strain hardening at high strain accurately as well as the variation of strain hardening with strain rate. © 2017, Editorial Department of Journal of Tongji University. All right reserved.