Influence of a new transverse sectorial breathing crack on the nonlinear dynamic characteristics of the composite rotating shaft-bearing system

In the inner shaft core and the outer shaft housing of a composite rotating shaft, the outer shaft housing will develop sector-like transverse breathing cracks due to fatigue during operation. In this study, the breathing mechanism of the transverse sectorial breathing crack is analyzed, and a new breathing function is formulated. The key parameters in this new breathing function are related to the shape of the crack, which is different from the traditional breathing function, in which the parameters were kept constants. By changing these key parameters, the new breathing function is not only applicable to the sectorial cracks but also to the transverse breathing cracks of various shapes. Then the dynamic equations of the crack-rotor-bearing system considering the gravity and axial loads are established using the finite element method. The effect of the crack on the system dynamic response is analyzed. There are significant nonlinear behaviors in the system dynamical response, and the super-harmonic resonances can be observed in the amplitude-frequency characteristic curves. Within the super-harmonic resonance region, the line shape of the system whirl orbits, the time history and phase diagram are closely related to the multiple of super-harmonic resonance. Determination of the axial location of rotor cracks plays a vital role in engineering applications. The frequency spectrums of system dynamic response are obtained using Fast Fourier Transformation to determine the crack location. The crack location can be also determined by analyzing the whirl orbits within the super-harmonic resonance region, as confirmed by the experimental verification.