Research On Fatigue Crack Growth Of A Crack Rotor

Cracks are the common faults for crack rotors. The crack will propagate under alternating loads until it breaks. Fatigue life can be predicted by analyzing the fatigue crack extension. Reasonable maintenance strategies can be made. Economic losses can be avoided because of the unexpected halt.First, in this paper, two types of crack fronts are studied. They are straight crack front and elliptical crack front. The concept of load spectrum is introduced. The crack depth ratio varied with the local flexibility coefficient and the crack shaft deformation ratios are discussed. Second, the two-parameter relationship of stress intensity factor, which accounts for the crack depth ratio and crack aspect ratio, has been determined. The crack aspect ratio and crack depth ratio have effects on stress intensity factor of elliptical front crack are discussed. According to the cracked shaft deformation, the load spectrum of crack shaft is calculated by flexibility analysis. Finally based on the cracked shaft material properties and fatigue characteristics, the fatigue propagation rate of the cracked shaft is calculated by employing four-parameter Forman formula.The result shows that the fatigue crack propagation on a shaft depends on the aspect ratio and the crack depth ratio. Because the aspect ratio of the crack is continuous changing during the fatigue crack propagation, the elliptical arc crack with a two-parameter stress intensity factor is necessary in this study. For a period of fatigue crack growth, the initial straight-edge or circular arc crack do not maintain the same crack aspect ratio, therefore, the elliptical arc crack is more realistic than the straight-edge crack and the circular arc crack.