Torsional vibrations are caused by periodic variations in the torque of the drive system as well as the torsional elasticity of the torque transmission components. An example of a source of torsional vibration may be the cranksets of a drive, e.g. an internal combustion engine or a power receiver.
Torsional vibrations become dangerous for the machine, especially in resonant zones, when the amplitude of torsional deflection becomes too high and the stresses occurring in the vibration node can exceed the permissible values and cause shaft fatigue and consequently its failure.