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 presented.) − (Formula presented.)) 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 presented.) − (Formula presented.) 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 presented.) curves before necking are determined using theoretical formulations. An inverse method based on finite element analysis is used to determine the (Formula presented.) − (Formula presented.) curves during the post-necking phase. The characteristics of (Formula presented.) − (Formula presented.) 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 presented.) curves. The constitutive model is further verified by comparing the finite element analysis and test results.