Hysteretic behavior and constitutive model of Q960E ultra-high strength steel under cyclic loading

The hysteretic behavior of Q960E ultra-high strength steel (UHSS) was thoroughly investigated through the experiments and was presented in this paper. Cyclic tests as well as monotonic tensile tests on totally sixteen Q960E UHSS coupons were conducted. The influence of strain amplitude, strain increment, the number of cycles and pre-strain on the hysteretic behavior of Q960E UHSS were investigated. Subsequently, number of cycles, cumulative energy dissipation and equivalent viscous damping ratio of Q960E UHSS, Q345B steel and Q460D steel were compared, with the differences in hysteretic behavior between UHSS and normal strength steel highlighted. It is also revealed that Q960E UHSS and Q345B have similar energy dissipation capacities, indicating that Q960E UHSS still has the potential to be used in seismic conditions after reasonable structural design. Moreover, the test results demonstrated that Q960E UHSS exhibits a significant cycle softening phenomenon compared to normal strength steel under cyclic loading. To define the cyclic stress–strain relationship, key parameters of two widely-used constitutive models (i.e. the Chaboche model and the Dong–Shen model) were calibrated and validated based on the data obtained from cyclic tests, with the uniform models also proposed in terms of different loading cases. The validation results indicated that both models can well predict the hysteretic behavior of Q960E UHSS, while the prediction accuracy of the Dong–Shen model is better than that of the Chaboche model due to the inclusion of deterioration of the elastic modulus and degradation of the strain hardening coefficient.