Coupled vibrations of a rotor with slant crack

A finite element model of a rotor with slant crack is presented. Based on fracture mechanics, a new flexibility matrix for the slant crack is derived that accounts for the additional stress intensity factors due to orientation of the crack compared to the transverse crack. Comparison between rotor with slant and transverse crack is made with regard to the stiffness coefficients and coupled vibration response characteristics. Compared to transverse crack, the stiffness matrix for slant crack is more populated with additional cross coupled coefficients. The influence of angle of orientation of the slant crack on the stiffness values is also investigated. Although the torsional stiffness is almost the same for both types of cracks, the larger cross-coupled stiffness values for slant crack leads to stronger cross-coupling in the bending–torsional–longitudinal vibrations compared to the transverse crack. Response-dependent nonlinear breathing crack model is used to evaluate response to unbalance and torsional excitation of the cracked rotor. The comparative study with transverse crack rotor is carried out to explore distinctive features in their response and suggest methodologies to diagnose them.