Dynamic behaviors of a two-crack rotor system under coupled bending and torsion excitations

To understand the nonlinear dynamic behaviors of a rotor system with two breathing cracks under the coupled bending and torsion excitations, this paper analyzes the vibration responses of the rotor system with different types of cracks (two transverse cracks, transverse-slant cracks and two slant cracks). The system stiffness matrix is derived based on the strain energy release rate theory, in which the interaction between two cracks is regarded as an additional flexibility coefficient. The breathing cracks are simulated by the crack closure line (CCL) model. The stiffness variation during one rotation cycle, and vibration response of the two-crack rotor system under the coupled bending and torsional excitations are simulated. Results show that crack breath leads to obvious nonlinear stiffness variation of the two-crack rotor system, and the breath behaviors of slant crack is influenced by torsional excitation. The crack types have a significant influence the crack breathing behavior and harmonic components of the two-crack rotor system. An apparent coupling bending-torsion vibration phenomenon can be found in the responses of the rotor system containing slant cracks. This study is expected to be helpful for health detection and fault diagnosis of cracked rotor systems.