Experiment study on the mechanical properties and constitutive model of grade 1960 steel wires under and after elevated temperatures

Abstract

To investigate the effects of different temperatures and cooling patterns on the surface characteristics, failure modes and mechanical properties of steel wires, a total of 52 steel wires of grade 1960 under and after elevated temperatures were tested. Then, the influence mechanism of temperatures on mechanical properties was further revealed with the help of SEM fracture scanning. Furthermore, the laws of reduction coefficient of mechanical properties of steel wires under and after elevated temperatures were proposed. Finally, the equation of high temperature stress-strain curve of steel wires was constructed. The results showed that the surface colors of steel wires gradually deepened with the increase of temperature, and a mass of zinc oxide particles appeared on the surface of steel wires at 500 °C, when the galvanized layer began shedding a lot. Meanwhile, the fracture shape of the specimens became obvious cup-cone, especially when the temperature exceeded 600 °C, the shape turned conical. In addition, the elastic modulus, yield strength and tensile strength of steel wires at 300 °C accounted for 85 %, 68 % and 74 % of the corresponding mechanical properties at room temperature, respectively. When the temperature exceeded 300 °C, the mechanical properties of steel wires would decrease significantly. For example, the ultimate strength of steel wire at 400 °C was only 53 % of that at room temperature. Nevertheless, the mechanical properties of steel wires after high temperature were basically unchanged before 300 °C. Similarly, the mechanical properties of steel wires gradually decreased after cooling by temperature action above 300 °C. For example, when the heating temperature was 600 °C, the ultimate strength was only 46 % of that at room temperature. Ultimately, comparing with the result of experimental and previous literature, the accuracy of the proposed formula for the reduction coefficient of high temperature mechanical properties and constitutive model of steel wire was verified. It is recommended to set the fire resistance temperature of steel wire inside the bridge cable at around 300 °C.