The Vibrational Behavior of a Multi-Shaft, Multi-Bearing System in the Presence of a Propagating Transverse Crack

Abstract

The effects of a transverse crack on the dynamics of a multi-rotor, multi-bearing system have been studied experimentally using a spin rig. It is concluded that except for very large cracks, the vibrational behavior is similar to that of a slotted shaft with additional excitation due to the crack opening and closing. It confirms the theory, described elsewhere, that it is possible to calculate the behavior of a cracked and/or slotted rotor for a realistic turbogenerator model for crack depths sufficient to give a measurable vibration vector change. The dynamic stresses in the cracked shaft were also measured. The results show how the dynamic bending moment at the crack tip depends on the speed of rotation of the shaft and the crack depth. The results are compared with a theoretical treatment previously reported and good agreement obtained. It is concluded that for crack depths in excess of one third the way through, the shaft the dynamic bending moment must be used for fracture mechanics calculations.