Constitutive model for full-range cyclic behavior of high strength steels without yield plateau

In order to characterize static and cyclic behavior of high strength structural steels, coupons made of two typical kinds of such steels in China, i.e. Q550 and Q690 steels with nominal yield strength of 550 MPa and 690 MPa respectively, were designed and tested under monotonic tension and a variety of cyclic loading protocols. Uniaxial stress-strain curves from the test show that for both steels no obvious yield plateau was observed, and short-range isotropic softening occurred right after initial yielding, while the subsequent strain hardening was contributed by both kinematic hardening and long-range isotropic hardening. Based on these phenomena, a constitutive model was developed specifically for those high strength steels and implemented in numerical analysis through user-defined subroutines. Calibration method for material parameters in this constitutive model was also established that mainly depends on tension coupon test result. After that, simulation was conducted by using the developed model with its stress-strain curves compared with those from cyclic loading test. Good agreement was obtained. Therefore, the constitutive model and its calibration method can be used for further seismic or dynamic nonlinear analysis of high strength steel structures and will help to develop reasonable and reliable ductile design method of those structures.