Notch fatigue fracture and crack growth behaviors on a steel sheet under out-of-plane bending

Abstract

For industrial products made of sheets, it is crucial to prevent the formation of fatigue cracks and the rapid destruction by stress risers. To carry out tests under out-of-plane bending load, this study used not only smooth sheet specimens made of a common structural steel, but also specimens with a through-wall circular hole in the center and specimens with a V-shape notch on one edge of the plate. The fracture mechanics parameters were investigated while fatigue crack initiation, growth, and the process leading up to a break were observed. In the high cycle region, the notch factor of the Hole specimen was 1.07, and that of the V-notch specimen was 2.22. With the same initial set stress amplitude, the V-notch specimen had fewer cycles at the time of crack initiation and faster crack growth rate than the Hole specimen. The state and the extent of crack initiation and growth were affected by the strain concentration and cyclic loading levels with different notch geometries. The threshold and unstable crack growth stress intensity amplitudes were identified, while the fracture mechanism and affecting factors were examined. By extending the Paris-Erdogan equation, a crack growth rate prediction model was proposed and validated with good approximation accuracy. It becomes possible to quantitatively predict the occurrence of fatigue, crack propagation, fracture, and fatigue life in industrial machinery and structures made of similar materials in out-of-plane bending.