Torsional Vibrations of Rotating Shafts

Abstract

A ROTATING shaft can exhibit torsional vibration when, because the dynamic coefficient of friction is less than the static value, the frictional force at the bearings supporting the shaft decreases as the shaft begins to rotate. The torque in the shaft when it begins to turn is greater than is required to overcome the running friction in the bearings, and the shaft accelerates and may overrun the drive until the speed of the shaft is reduced to zero. Then superposed on the steady rotation of the shaft there is a vibration of an amplitude such that the instantaneous angular velocity of the shaft varies between zero and rather more than twice the mean value. So-called ‘stick-slip’ vibrations of this type are well known—they may, for example, be responsible for brake squeal in automobiles.