Research On Dynamic Behaviors Of A Semi-Elliptical Cracked Rotor System

Shafts are among components subjected to, perhaps, the most arduous working conditions in high-performance rotating equipment used in process and utility plants. Due to manufacturing flaws or cyclic loading, cracks frequently appear in rotating machinery. The growth of cracks in the rotating components can cause severe accidents if undetected. In many of those works, a straight edge is usually considered to idealize the surface crack front. However, both the theoretical analysis and experimental observations show that the maximum stress intensity factor (SIF) is attained at the deepest point on the crack front for the initial straight edge crack. The growth rate of the crack front around deepest point is faster than that at the intersection with the surface. Consequently, a straight-fronted transverse crack tends to become curved. So in this paper, what mainly discussed about is semi-elliptical front crack.Domestic and foreign Present state of making researches on the stress intensity factor for semi-elliptical surface crack with non-dimensional crack depth、crack shape and crack position are presented. Since a crack mainly affects the stiffness of a rotor system, the dissertation discusses how to obtain the stiffness of a cracked rotor. Firstly, the stiffness model of crack element was calculated using theories of fracture mechanics. The influence function analysis on stiffness and crack displacement as a function of crack depth and crack shapes under static load were given. Crack breathing behaviors and time-varying stiffness were modeled for each crack element using Crack Closure Line Position (CCLP), and based on that, some comparison about breathing behaviors and stiffness under different crack depth between straight front and semi-elliptical front crack were discussed. Secondly, Runge-Kutta numerical method is used to solve motion equations of cracked rotor system. It is easily found that 1X、2X and 3X were emerged from time and frequency figure, and discussed the influence of crack depth and crack shapes to frequency.