Low-cycle fatigue properties of bimetallic steel bars after exposure to elevated temperature

Abstract

The BSB (bimetallic steel bar) has a broad application prospect in RC (reinforced concrete) structures servicing in corrosive environment. To determine seismic resistance of RC structures, it is important to clarify the low-cycle fatigue properties of reinforcement. Fire has lasting effects on mechanical properties of BSB. To value the service performance of RC structures after fire, the low-cycle fatigue properties of BSB are investigated experimentally. After elevated temperature, the substrate and cladding layer are still tightly bonded. When exposure temperature is relatively high (800 °C and 900 °C), there is martensite formed because of the quenching treatment. When the exposure temperature is lower than 700 °C, the hysteresis curves perform the full rhombus. When the exposure temperature ranges from 700 °C to 900 °C, the hysteresis curves become slender and the maximum tensile and compressive stresses increase. The models for predicting the cycles to failure and total dissipated energy density are proposed, which can predict the low-cycle fatigue properties of BSB after exposure to elevated temperatures. The comprehensive discussion between metallographic structures and low-cycle fatigue properties is performed. When the exposure temperature ranges from 300 °C to 700 °C, BSB specimens perform the ductile fracture failure. The intergranular embrittlement of martensite leads to the intergranular failure of BSB specimens exposed to 800 °C and 900 °C.