Ductile fracture of high-strength bolts under combined actions at elevated temperatures.

Steel bolted connections are critical structural components that can initiate progressive collapse at ambient and elevated temperatures. High-strength bolts are highly vulnerable members due to rapid strength degradation at high temperatures. This paper presents a numerical study on the ductile fracture of the frequently used Grade 8.8 and 10.9 structural bolts under tension, shear, and combined forces at 20–700 °C. True stress–strain curves have been defined up to fracture for both grades. The fracture parameters have been calibrated by a total of four experiments: two tensile and shear tests for each grade. The ductile fracture models with proposed fracture parameters have been further validated by pretensioned shear tests at elevated temperatures. The relationship between equivalent strain and triaxiality was investigated based on the numerical results. In general, equivalent plastic strain values become larger with increasing temperature. The fracture analysis with given ductile fracture parameters estimates the test results with reasonable accuracy under all failure modes. The fracture model can be used in numerical analysis to investigate the ductile failure of the high-strength bolted connections at ambient and elevated temperatures. Furthermore, the influence of displacement at fracture values on the results was investigated by a three-bolted inclined shear test. • A ductile fracture model is proposed for Grade 8.8 and 10.9 bolts up to 700°C. • The proposed fracture model agrees well with the validation test results. • Fracture models given in literature are compared for bolts at elevated temperatures. • A linear relation is seen in PEEQ and stress triaxiality in tensile tests. • In general, the ductility of bolts increases with temperature rise. • The fracture at displacement value effect is not found significant under shear load. [ABSTRACT FROM AUTHOR]