Constitutive Model for Equivalent Stress-Plastic Strain Curves Including Full-Range Strain Hardening Behavior of High-Strength Steel at Elevated Temperatures

High-strength steel has been increasingly applied to engineering structures and inevitably faces fire risks. The equivalent stress-plastic strain ([Formula: see text] − [Formula: see text]) curves of steel at elevated temperatures are indispensable if a refined finite element model is used to investigate the response of steel members and structures under fire. If the tensile deformation of steel is considerable, the [Formula: see text] − [Formula: see text] curves at elevated temperatures are required to consider the strain-hardening behavior during the post-necking phase. However, there is little research on the topic. Based on the engineering stress-strain curves of Q890 high-strength steel in a uniaxial tension experiment at elevated temperatures, the [Formula: see text] curves before necking are determined using theoretical formulations. An inverse method based on finite element analysis is used to determine the [Formula: see text] − [Formula: see text] curves during the post-necking phase. The characteristics of [Formula: see text] − [Formula: see text] curves, including the full-range strain hardening behavior at different temperatures, are discussed. An equivalent stress-plastic strain model of Q890 steel at elevated temperature is proposed, which is consistent with the [Formula: see text] curves. The constitutive model is further verified by comparing the finite element analysis and test results.