Experimental and modelling study of cyclic plasticity of high strength steel Q690

High strength steels (HSSs) have received attention in the research community over the past few years owing to their high strength-to-weight ratio. This study examined the cyclic plastic behaviour of HSS Q690 under various cyclic loading protocols via experimental investigation, and a constitutive model was subsequently proposed. The strain amplitude and mean strain were the key parameters for constructing the cyclic loading protocols. The test results indicated that the peak stress of each cycle decreased with increasing equivalent plastic strain, which confirmed the cyclic softening behaviour. The peak stress evolution was also observed to be independent of the maximum strain amplitude, but dependent on the current strain amplitude, which proved the absence of the strain range memory effect. Furthermore, the cyclic plastic response of Q690 steel was comprehensively examined within the framework of metallic cyclic plasticity, including kinematic hardening, isotropic hardening/ softening, and elastic modulus evolution. The kinematic hardening of Q690 steel was proven to be dependent on the equivalent plastic strain and the current plastic strain amplitude, whereas its isotropic hardening/softening was determined only by the equivalent plastic strain. It was also observed that the elastic modulus decreased to a stable value with increasing equivalent plastic strain. A new constitutive model was proposed to quantify these cyclic plastic features. The proposed model provided an excellent prediction of the cyclic response of Q690 steel under all loading protocols. The relative error between the simulated results and the test results was within a narrow band between -5% and 5%.