Fracture behavior of high-strength steels at elevated temperatures

Abstract

High-strength steels have been increasingly applied in different categories of structures due to their advantages of high strength and light weight. Fracture in high-strength steel members becomes more essential when exposed to fire, which governs the overall strength and deformation capacity of steel structures. This paper presents the studies on the elevated-temperature fracture behavior of high-strength steels with the yield strengths ranging from 460 MPa to 960 MPa. A fracture prediction approach is first proposed for Chinese Q690 steels. Using experimental data together with finite element analysis, true stress-strain curves considering post-necking behavior, stress modified critical strain model (SMCS) and damage evolution law are calibrated and validated for Q690 steels at elevated temperatures. The proposed fracture prediction approach is then applied to other high-strength steels (Q460, Q550, Q890, S460, S690 and S960). The results show that different high-strength steels with similar strength grade may exhibit quite different fracture behaviors at given temperature. However, their variation trends of the post-necking material properties including slope of post-necking true stress-strain curves and fracture toughness index with temperature were relatively consistent. These high-strength steels may exhibit different variations of damage evolution law with temperatures. The proposed post-necking material properties can reasonably predict the fracture behavior of these high-strength steels at elevated temperatures.