Rotor crack breathing under unbalanced disturbance

Abstract

Rotor cracks are a type of failure seriously affecting the safe operation of rotating machinery. It has been reported that cracks under the dominant effect of gravity produce a breathing effect and consequently result in an abnormal vibration of the rotor. However, in practice the rotor cannot avoid unbalance disturbances. As the rotational speed of the rotor continues to rise, unbalance replaces the dominant role of gravity and changes the breathing pattern of cracks. Therefore, this work aimed to study the crack breathing process during the acceleration phase of an unbalanced cracked rotor by coupling the strain energy release rate (SERR) technique with the neutral axis (NA) method. It was found that when the unbalance is dominant, the fracture surface remains fixed instead of being uniformly open and closed. That is, during the entire acceleration phase of the rotor, the crack undergoes a process from uniform breathing to breath-hold breathing. The change of breathing mode induces the whirl phenomenon in the cracked rotor, which gradually disappears with increasing unbalance. This whirl phenomenon can be combined with superharmonic resonance characteristics as an assessment tool for crack fault diagnosis. The above findings are helpful in diagnosing rotor cracking faults under unbalanced disturbances.