STUDY ON FATIGUE CRACK GROWTH BEHAVIOR OF Q345R STEEL UNDER MULTIPLE OVERLOADS

Single overload may lead to the retardation of fatigue crack propagation, and thus the elongation of fatigue life. However, the effect of multiple overloads on the fatigue crack propagation behavior remains unaddressed. The compact tension specimens made by Q345R steel are used to study the influence of multiple overloads during the constant amplitude loading on the subsequent fatigue crack growth behavior. The results show that the retardation effect increases at first and then decreases with the increase of the overload interval under the same R-ratio, overload applying crack length and overload ratio. da/dN_min reaches the minimum when the overload interval is half cycle of a single tensile overload retardation zone, and the retardation effect of overload is the most obvious. The modified Wheeler model which includes overload interaction parameter Ø_I is used to predict the crack growth rate with multiple overloads. The predict results show good agreement with the test results.