Study on dynamic mechanical behavior of Q460JSC and HQ600 high strength steel

High-strength steel has been gradually applied in practical engineering and achieved good economic and social benefits. Due to the threat of terrorist attacks and accidental explosions, high-strength steel structures need to have high blast resistance. However, the studies on the mechanical properties and constitutive equations of high-strength steels under high strain rate are insufficient. The research on the anti-explosion properties of high-strength steel structures lacks material models and constitutive parameters. Therefore, this paper investigated the quasi-static and dynamic mechanical properties of Q460JSC and HQ600 high strength steels. A series of quasi-static tensile, high-speed tensile and SHTB tests were conducted to obtain the material properties under different strain rate in the range of 0.00025 s−1 to 5000 s−1. Combined with finite element simulation by LS-DYNA, the strain hardening relationship of specimens after necking was treated by inverse extrapolation method, and the true stress-strain curves at different strain rates were obtained. The effects of strain rate on materials strength and plasticity were analyzed. The quasi-static and dynamic constitutive parameters of these two high strength steels were fitted by Ludwik criterion and modified Johnson-Cook model, respectively. The results show that the yield strength, ultimate strength and fracture strain of these two kinds of high strength steels all increase with the increase of strain rate, but the uniform elongation is not sensitive to strain rate. The change of strength is not obvious in the strain rate range of 103. The inverse extrapolation method is effective in dealing with the true stress-strain curve after necking, and more accurate results can be obtained by continuously optimizing the strain hardening index. The improved Ludwik criterion and the new Johnson-Cook model correction formula can well describe the stress-strain relationship of these two high-strength steel materials in the range of 10−3 s−1 to 103 s−1, which provide basis for the investigation on anti-explosion properties of high-strength steel structures.