Constitutive Relationships of Grade 10.9 High-Strength Ring Groove Rivets at Elevated Temperatures

High-strength ring groove rivets are increasingly used in structural engineering. In order to investigate the mechanical properties of high-strength ring groove rivets at elevated temperatures and to establish the high-temperature constitutive relationships, thermal expansion tests and high-temperature tensile tests were conducted on the material samples of rivet shank and collar. The thermal expansion coefficients of the two materials were obtained, and the prediction formulas were fitted. Through the high-temperature tensile test, the stress–strain relationship, as well as the elastic modulus, yield strength, and ultimate strength, among others, were obtained. The reduction factors of the mechanical properties were fitted, and the prediction formulas were proposed. The Wang model and Ramberg–Osgood (R-O) model were used to establish the constitutive relationships of the two materials, and the prediction formulas of the relevant parameters at elevated temperatures were determined. The two models were compared with the actual test curves. The results showed that the formulas proposed based on the fitting of test results can predict the mechanical properties of the materials quite well. The material strength of rivet shank and collar generally decreased with increasing temperature. The collar material showed blue brittleness at around 300°C, leading to an increase in strength at this temperature. The R-O model can only provide the curve before ultimate strength, whereas the Wang model is able to represents the entire stress–strain curve. The Wang model determined in this study can describe the constitutive relationships of the rivet shank and collar at any temperature from 20°C to 900°C.