Rotating machinery is one kind of mechanical equipment most widely used in the industrial department. As the key component of rotating machinery, the rotor system often has cracks, which lead to the failure of the rotating equipment, resulting in economic losses and even causing machine damage and casualties. In this paper, I establish the finite element model of cracked rotor, and apply the torsional harmonic excitation to the cracked rotor. The time domain and frequency domain analysis methods are used to research the vibration response of the cracked rotor under torsion. When the frequency of torsional excitation equals the natural frequency of bending vibration, the rotational frequency can be found in the spectrum of transverse vibration due to the interaction between the torsional excitation frequency, the rotational frequency and the generated harmonics. This phenomenon indicates that bending and torsion coupled vibration occurs in the cracked rotor system at this time. Bending and torsion coupled vibration occurs in a rotor with a slant crack, which does not occur in a rotor with a transverse crack. In addition, the effects of crack type and relative depth on the vibration response of the system are further studied. This paper provides a theoretical basis for on-line identification and detection of cracked rotor.
