Constitutive and Fracture Models of Q345E Ship Steel Considering Stress State

In order to characterize the mechanical response of Q345E steel under high-speed impact conditions, the quasi-static tensile and Hopkinson compression experiments are conducted to determine the static and dynamic mechanical properties of Q345E steel as well as its fracture characteristics in wide stress triaxiality. Based on the Johnson-Cook (JC) and Cowper-Symonds (CS) models, a JC-CS constitutive model is proposed to characterize the static and dynamic mechanical behaviors of Q345E steel. A three-stage Wierzbicki fracture model is proposed and the failure parameters in the range of each stress triaxiality are obtained through experiment and numerical simulation. The Abaqus VUMAT subroutine is used to verify the validity of the constitutive and fracture models. The results show that Q345E steel has obvious strain hardening and strain rate effects, and the two kinds of effects are coupled under dynamic loading. The proposed JC-CS constitutive model can accurately characterize the rate-dependent strain hardening and strain rate effects in the range from quasi-static to high strain rate. The fracture strain of Q345E steel is related to the stress triaxiality. When the stress triaxiality is greater than -1/3 and less than 2, the fracture strain decreases first and then increases, and finally tends to zero. The fracture strain becomes infinitely large when the stress triaxiality tends to -1/3. The numerically simulated results demonstrate that the fracture morphology, the failure mode of target plates and the process of penetrating a multi-layer target predicted by the simulation are highly consistent with the experimental results. This indicates that both the proposed JC-CS constitutive model and Wierzbicki fracture model effectively capture the mechanical properties and fracture behavior of Q345E steel as well as its response characteristics under high-speed impact.