A 3D constitutive model of high-strength constructional steels with ductile fracture

Abstract

High Strength Structural (HSS) steels, with nominal yield strength not less than 460 MPa are rapidly gaining popularity in steel construction worldwide. These steels exhibit phenomena, such as the Lode angle dependence of yield and accelerated cyclic softening at large accumulated plastic strains, which cannot be conveniently simulated by existing constitutive models that are developed primarily for normal strength structural steels. Moreover, in the area of steel structures, the failure location of steel members is generally undergoing large plastic deformation at triaxial stress states. In order to describe and predict cyclic behavior of HSS steels under multi-axis stress states, a new cyclic constitutive model with the consideration of accumulative damage and the influence of triaxial stress states based on ductile fracture model is formulated to simulate the response of HSS steels subjected to a range of loading types in terms of triaxial stress state and loading histories. The proposed model, termed as HSS-3D, is calibrited by experimental results consisting of coupon scale monotonic and cyclic tests. It is determined that the HSS-3D model shows significant improvement in accuracy for HSS steels compared to the commonly used Armstrong Frederick model. The proposed HSS-3D model is able to simulate: (1) the Lode angle dependence through an enhanced yield function which modifies the conventional von Mises yield surface; (2) the deterioration of the elastic region at high accumulated strains through new isotropic softening relationship; (3) the influence of stress states on strength softening behavior of HSS steels and (4) ductile fracture of steels under cyclic loading.