Mechanical properties and constitutive model of cold-formed Q1100 ultra-high strength steel sections at low and elevated temperatures

Abstract

The Q1100 ultra-high strength steel (UHSS) has broad application prospects in bridges and super high-rise buildings due to its ultra-high strength properties. However, no research has been conducted on the mechanical properties of Q1100 UHSS at low and elevated temperatures. Therefore, an experiment was conducted to examine the low- and elevated-temperature mechanical properties of Q1100 UHSS at the flat and corner regions of cold-formed angle sections. The temperature considered in this study ranged from −80 ℃ to 500 ℃. The failure modes, stress-strain curves, and key mechanical parameters of the flat and corner specimens of Q1100 UHSS at different temperatures were obtained. The experimental results showed that both the flat and corner specimens underwent ductile fracture with obvious necking at different temperatures. The stress-strain curves of all specimens had no yield plateau, showing obvious nonlinear characteristics. The strength properties of Q1100 UHSS at low temperatures were increased by less than 10 %. However, the strength properties of Q1100 UHSS at elevated temperatures were significantly reduced, where the reduction exceeded 60 % at temperatures reaching 500 °C. Notably, the ultimate strength of Q1100 UHSS at 200 °C was about 5 % higher than that at ambient temperature. The cold-forming process significantly reduced the ductile properties of Q1100 UHSS, but improved its strength properties. At low and elevated temperatures, the most significant cold-formed strengthening effects of yield strength, ultimate strength, and elastic modulus occurred at −40 ℃ and 300 ℃, respectively. Moreover, the predictive equations of key mechanical parameters and a two-stage constitutive model were proposed for the Q1100 UHSS flat and corner specimens. The verification results indicated that the proposed predictive equations and constitutive model could accurately predict the mechanical parameters and stress-strain curves of the Q1100 UHSS flat and corner specimens at different temperatures. The experimental results and constitutive model provided a basis for the numerical and theoretical studies on the resistant performance of the cold-formed UHSS structures servicing in low and elevated temperatures, which could be used as the material model.