High strain and low cycle fatigue behaviors of rebars produced by QST and V-N microalloying technology

Based on the failure model of rebars in reinforced concrete structures (RCS) under earthquake loading, total strain controlled high strain and low cycle fatigue (HSLCF) behaviors of 400 MPa grade 16 mm diameter rebar produced by V-N MA (Microalloying) and QST (Quenched and Self-Tempered) were tested at room temperature. Through the fittings of Coffin–Manson and Hollomon relationship, the rates of energy-absorption under seismic loading was proposed, which was defined as cyclic toughness. The test results showed that although the static mechanical properties of two types of rebars is similar, the V-N MA rebar exhibit higher cyclic toughness, fatigue life and stress amplitude under constant strain amplitude, as well as the transition fatigue life than the QST rebar, suggesting it will have better seismic performance under seismic loading. Additionally, to understand the microstructural basis for this difference in performance, broken specimens were examined using both scanning (SEM) and transmission (TEM) electron microscopy.