Crack effects in rotordynamics

Cracked rotating shafts have been the object of studies and investigations since the 1960s. It seems that the first paper on cracked structures has been published in 1957, therefore we now have a story lasting almost 50 years. Important achievements have been made during these years, the knowledge of the dynamical behaviour of cracked shafts has allowed to recognize the presence of a crack and to stop the cracked shafts in time before catastrophic failures. Close inspections revealed that in many shafts the crack had already propagated up to a depth of almost 50% of the diameter, which is obviously a very critical situation. Bearing in mind the fact that it is generally believed that propagating velocity increases exponentially, in many of these cases some days of operation would have been sufficient to provoke a catastrophic failure, with the loss of the complete machine train and with high risks for people and other equipments. In some cases instead the machines burst, generating catastrophic failures with heavy damages to the plants. Very high costs were involved in the reconstructing of the machines and the complete plant, as well as in the lost production for several years