High-strength steel has been increasingly applied to engineering structures and inevitably faces fire risks. The equivalent stress-plastic strain (σeq- εeqp) 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 σeq- εeqp 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 σeq-εeqp curves before necking are determined using theoretical formulations. An inverse method based on finite element analysis is used to determine the σeq- εeqp curves during the post-necking phase. The characteristics of σeq-εeqp 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 σeq-εeqp curves. The constitutive model is further verified by comparing the finite element analysis and test results.
Keywords: constitutive model; elevated temperature; equivalent stress-plastic strain curves; high-strength steel; inverse finite element analysis; necking.