On the stability of cracked rotor systems

The stability of cracked rotor systems is studied from the aspect of input-output stability and system stability. The system stability describes the influence of the size and the position of a fatigue crack on the stability. The input-output stability represents the influence of rotating speeds together with natural frequencies of the system on the stability. By introducing the concept of virtual oil-film bearing, reasons for the system instability is interpreted. It is suggested that fatigue crack is an important reason for the existence of lower frequency vibration components in some turbo-machines and a small fatigue crack may drive a system into instability in a very short time. One numerical example and one experiment example are presented at the end of the paper.