Some remarks on breathing mechanism, on non-linear effects and on slant and helicoidal cracks

The breathing mechanism of cracks in rotating shafts is accurately investigated by means of 3D non-linear models. The behaviour is then modelled by means of a much simpler approximated approach, which allows also to calculate the stiffness variation of the cracked shaft. This simple model has then been used for analysing non-linear dynamic behaviour of cracked rotating shafts, which occurs when breathing is governed by the vibration itself. Finally, also the effects of cracks which have developed according a helix, instead of developing on a cross section, due to the combined action of bending and torsion, are investigated. The breathing behaviour and still more the deflections are then influenced by the torsion. The aim of these investigations is mainly to present behaviours of full size industrial machinery, computed numerically with finite element models of the shaft.