Identification of transverse crack position and depth in rotor systems

This paper introduces a method for the identification of the position and the depth of a transverse crack in a rotor system, by using vibration measurements. As it is reported in literature and from field experience, a transverse crack modifies the dynamic behaviour of the rotor, generating in a horizontal axis shaft periodical vibrations with 1x, 2x and 3x rev. components. A model based diagnostic approach and a least squares identification method in the frequency domain are used for the crack localisation along the rotor. The crack depth is calculated by comparing the static bending moment, due to the rotor weight and to the bearing alignment conditions, to the identified “equivalent” periodical bending moment, which simulates the crack. Finally, the validation of the proposed method is carried out statically and dynamically by means of experimental results obtained on a test rig.