A combined model based fatigue life assessment method for a breathing cracked rotor

Fatigue life assessment is crucial for a safe operation of rotating machinery. Fracture mechanics is commonly used to evaluate the fatigue life in literature. However, the dynamic response when the rotor starts to rotate is rarely considered which has important influence on the fatigue propagation. In this paper, a novel methodology for fatigue life assessment of a breathing cracked rotor was proposed based on the rotor dynamics and fracture mechanics theory. Mathematical functions proposed by a published paper were utilized to represent the breathing process of the crack, and system response of the cracked Jeffcott rotor was analyzed. A 3D finite element model (FEM) of the cracked rotor was established in ANSYS. The breathing mechanism and dynamic response were then introduced to the 3D FEM so as to derive the dynamic stress intensity factors (SIFs) during the rotor rotation, by which way the closing and opening effect was considered. The modified Paris' law was used to assess the fatigue life of the cracked rotor with the effective SIF range obtained from FEM analysis process. The simulation results of one case study show that the proposed method is effective in fatigue life assessment for breathing cracked rotors.