Mechanism explanation and experimental verification of a new modulation frequency characteristic in a disturbed crack rotor

The research on the vibration response characteristics and mechanism of the cracked rotor system can provide an important reference for the crack identification. However, at present, the researches mainly focus on vibration response of steady-state and start-up or run-down process, except the disturbed state (an intercepted short transient process before the system turns into a steady state). In this paper, a novel modulated frequency characteristic is found in a disturbed state by cracked Jeffcott rotor model. Then, to promote readers’ understanding of the causes of the new modulation phenomenon, the modulation mechanism is explained by the analytical derivation of the stiffness breathing functions and the additional stiffness excitations. Furthermore, the variation of the modulation frequency amplitudes with the crack depths in the speed disturbance state is further studied, and a method for monitoring the crack severity based on the ratios of the modulation frequency amplitudes is presented. Finally, the modulation characteristic in a disturbed state is verified by the speed disturbance experiment of a cracked rotor system. The disturbed state is a new aspect to study the vibration response characteristic of a cracked rotor and the modulation frequency found in this paper is a possible supplement for the crack identification and may provide some references for the crack monitoring.