Crack Modelling

Cracked rotating shafts have been the object of studies and investigations since the 1970s, even if some failure cases are also reported during the 1950s (see section 1.2), therefore now we have a story lasting about 50 years. Important achievements have been made during these years, the knowledge of the dynamical behaviour of cracked rotors has allowed the presence of cracks to be recognized and cracked rotors to be stopped in time before catastrophic failures. Accurate inspections revealed that cracks had already propagated up to a depth of almost 50% of the diameter in many shafts (see for instance figure 2.15), 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 further days of operation would have been sufficient to provoke a catastrophic failure, with the loss of the complete machine train and high risks for people and other equipment; also the loss of production of the unit, before the replacement with a new unit, is a comparable economic loss.