Experiment research on rate-dependent constitutive model of Q420 steel

The strain rate effect on the progressive collapse resistance of steel structures under abnormal events or impulsive loading should not be neglected because the constitutive properties of steels change significantly with the loading time. The rate-dependent constitutive properties of Q420, which is a low-alloy high strength structural steel in China, are different with those of the low carbon steel Q235 and the low alloy steel Q345 because of the different manufacturing techniques and micro alloying elements. Quasi-static and dynamic uniaxial tensile tests within the range of 0.001-288 s−1 strain rates were carried out to study the rate-dependent mechanical properties of Q420 steel by INSTRON and Zwick/Roell HTM5020 testing machine. Three dimensional finite element (FE) models are developed to predict the true stress-strain relationships of Q420 steel beyond necking under different strain rates by a hybrid experimental-numerical method. The Cowper-Symonds model is verified to be capable of describing the dynamic behavior of Q420 steel at the lower strain rates. The modified H/V-R model established by introducing the dynamic increase factor of Cowper-Symonds model into the H/V-R constitutive model is better to predict the strain rate effect of Q420 steel than the H/V-R model.