Application of empirical mode decomposition to a Jeffcott rotor with a breathing crack

Fatigue damage, appearing due to developing cracks, is considered to be one of the main faults in rotating machinery. The damage in rotating components can be catastrophic, posing a potential hazard and leading to significant economic loss. In the related literature, transverse breathing cracks are considered as a primary mode of damage. Accordingly, a Jeffcott rotor with a transverse breathing crack has been examined here wherein a method for identifying the early crack propagation is proposed. The breathing functions developed in a recent publication to approximate the actual breathing mechanism of the cracked shaft are employed along with the method of empirical mode decomposition (EMD) to identify the crack vibration signature. EMD combined with the wave transform spectrum is used to decompose the measured vibration time series of the cracked rotor system into nearly monochromatic components. It is shown that the variations of the averaged amplitudes of the super-harmonic components in the neighborhood of 1/2 and 1/3 of the first critical rotational speed provide clear and robust vibration signatures indicating the early presence of the breathing crack. This signature is utilized here for early crack detection in the rotor system under consideration.