EXPERIMENTAL STUDY ON THE FATIGUE CRACK GROWTH BEHAVIOR OF BRIDGE STEEL Q345qD AT LOW TEMPERATURES

To explore the fatigue crack growth behavior of bridge steel used in cold regions, a series of experimental studies, including Charpy impact test, fatigue crack growth rate test and fatigue crack growth threshold test, were carried out for bridge steel Q345qD with a plate thickness of 16 mm at room and low temperatures. The results show that the impact energy and percentage shear area reduce as the temperature declines. At stress ratios of 0.1, 0.2 and 0.5, the fatigue crack growth rate becomes lower with the declining temperatures, and the fatigue ductile-brittle transition temperature of the bridge steel is below -60℃. The fatigue crack growth rate is insensitive to the variation of the stress ratio at both room temperature and low temperatures. At the stress ratio of 0.1, the fatigue crack growth threshold increases with the reduced temperature. It can be concluded that this batch of bridge steel exhibits good resistant performance to fatigue crack growth at low temperatures, making the prevention of low-temperature brittle fracture become the first consideration. The experimental data obtained can be employed for further study on the fatigue & fracture resistant design and fatigue residual life prediction of fatigue detail for steel bridges in cold and extremely cold regions.