Vibrational characteristics of a cracked rotor subjected to periodic auxiliary axial excitation

Abstract

Rotor failure due to cracks can be catastrophic with large costs in down time, damage to equipment and injury to personnel. Prevention of such problems is only attained by developing reliable methods for crack detection and diagnosis. In this paper, the vibratory response of a cracked rotor to an auxiliary axial excitation is investigated experimentally for the purpose of crack detection. An open crack (slot) is artificially created in the rotor-shaft of the experimental rig. The effects of running speed, crack depth and crack-unbalance angle variations on the vibratory response are investigated experimentally. It is shown that the auxiliary excitation method can be efficiently used in crack detection as an online condition monitoring technique. By properly choosing the frequency of the periodic axial excitation and the running speed, the presence of a crack in the excited shaft can be ruled out and the crack growth can be monitored. The crack-unbalance angle can influence the identification process negatively by masking the crack effect on the vibratory response. However, an unbalance trial mass test can help in finding out the unknown crack angle.