  In this paper, the influence of transverse cracks in a rotating shaft is
analysed. The paper addresses the two distinct issues of the changes in modal
properties and the influence of crack breathing on dynamic response during
operation. Moreover, the evolution of the orbit of a cracked rotor near half of
the first resonance frequency is investigated. The results provide a possible
basis for an on-line monitoring system. In order to conduct this study, the
dynamic response of a rotor with a breathing crack is evaluated by using the
alternate frequency/time domain approach. It is shown that this method
evaluates the nonlinear behaviour of the rotor system rapidly and efficiently
by modelling the breathing crack with a truncated Fourier series. The dynamic
response obtained by applying this method is compared with that evaluated
through numerical integration. The resulting orbit during transient operation
is presented and some distinguishing features of a cracked rotor are examined.
