oscillations of structural elements and parts of machines, manifested in periodically varying torsional strain.
An example of torsional oscillations is the harmonic motion of a torsion pendulum in the form of an elastic rod fastened at one end and with a massive disk at the other. The torsional oscillations of a pendulum are used in various physics instruments, for example, to determine the elastic modulus of shear, the coefficient of internal friction of solids, and the coefficient of viscosity of liquids. In structures of machines and mechanisms, torsional oscillations are usually an undesirable feature. This is especially true for the crankshaft of piston internal-combustion engines. For example, when the frequency of the variable torque arising during the operation of the engine coincides with one of the natural torsional oscillations of the engine shaft, large resonance torsional oscillations of the shaft may arise, which may lead to breakage of the shaft. Under certain flight conditions, the action of aerodynamic forces sometimes leads to self-excited flexural torsional oscillations of the wings of aircraft (flutter), which may lead to destruction of the wing.