The Crack Propagation Rate According to Notches and Overload Levels

Abstract Fatigue experiments were performed on SEN specimens of EN AW 7475-T761 in order to investigate cyclic lifetime changes due to sharp notches and periodic overloads. While for specimens with sharp notches one would expect a decrease in cyclic lifetime, the introduction of periodic overloads generally causes a lifetime extension. Therefore specimens with three different notch depths but constant notch radius, and consequently three different elastic notch factors, were combined with three different overload levels and two different overload types. On the fracture surfaces a decrease in the crack propagation rate to a certain distance was observed which was followed by an increase of the crack propagation rate till fracture. The different distances to the minima of the crack propagating rate depend on the type and the level of the periodic overload as well as on the notch depth. A significant fatigue life extension due to periodic overloads introduced into a constant amplitude load could be obtained for pure tensile overloads with high overload levels.