Longitudinal and torsional vibrations in rotors with transverse cracks

In a rotating shaft with a crack, the bending, longitudinal and torsional degrees of freedom are linked. This paper presents a crack model which for the first time takes all six beam degrees of freedom into account for the open crack. The statements lead to a finite rigidity matrix and a transition matrix for a crack beam element. The model concepts known to date can be consistently generated as special cases from the new crack model. Depending on the motion condition, equations of motion with non-linear or periodically time-variant character are obtained. The longitudinal and torsional vibration behaviour under weight-dominant conditions are examined more intensively with the example of a large turbine. It is shown that the vibration components in harmony with the rotation can be used to identify the location and depth of the crack. (orig.) With 88 figs