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.

A cracked beam finite element for rotating shaft dynamics and stability analysis

“…To reduce the difficulty of the problem in the study of cracked shafts, researchers often assumed that the amplitude of the vibrations due to the presence of cracks is weak compared to those of the vibrations due to permanent loads [El Arem and Nguyen 2006;Gasch 1976;Mayes and Davies 1976;1980;Davies and Mayes 1984;Henry and Okah-Avae 1976;Gasch 1993]. The present model is more general and allows us to overcome the limitations of such an assumption.…”

The influence of cracks in rotating shafts

“…Various theoretical and experimental works [3][4][5][6][7][8][9][10] performed over the last three decades have indicated that the change in modal properties (natural frequencies and modes shapes) may be useful for the detection of a crack, as well as for the identification of both crack depth and location. Moreover, the influence of opening and closing of crack due to the shaft self-weight for various orientations of the shaft has been investigated [3,11] and showed the effectiveness of the change in natural frequencies versus the orientation of the shaft to detect the orientation of the crack front.…”

Vibrational Analysis in Condition Monitoring and faults Diagnosis of Rotating Shaft - Over View

“…Inagaki [7], Mayes [8], and Nelson [9] investigated a general rotor system with a transverse crack using methods such as the transfer matrix method, and finite element method. Some of them [7,10] performed experiments using a test rotor and compared with theoretical results. The propeller-bearing-shaft system has been holistically modeled using FE procedure with the actual in-situ profiles for the propeller, bearings, supports and torque loading aluminum arm.…”