Fatigue crack propagation performance of Q690 high-strength steel and butt welds

The fatigue performance of high-strength steels is an important issue in bridge engineering. In this study, fatigue crack propagation rate tests and theoretical studies of high-strength steel Q690 base material and butt welds were conducted. Two types of compact tensile (CT) specimens-one for the Q690 compact tensile specimens and the other for the butt welds-were used for the test under stress ratios of R = 0.1, 0.3, and 0.5, with a loading frequency of 15 Hz. The fatigue crack length was measured using the flexural method with an extensometer, and the load value and the corresponding cycle number in the tests were also obtained. These results were processed using the seven-point polynomial method to obtain the fitting curve of log (da/dN) to log & UDelta;K. Finally, the modified Paris formula of Q690 was presented, and the corrected values of the material parameters C and m were determined. The test results show that the fatigue crack propagation rate of Q690, both for the compact tensile specimens and those with butt welds, increased with the stress ratio R. The fatigue crack propagation rate of Q345qD was 1.8 times higher than that of Q690 high-strength steel. In addition, the fatigue resistance of Q690 was significantly higher than that of other standard steels. The fatigue crack propagation rate of the Q690 specimens with butt welds at a low-stress amplitude was lower than that of the Q690 compact tensile specimen. At a high-stress amplitude, the fatigue crack propagation rate of Q690 is greater than that of the Q690 compact tensile specimen.