Torsion

This is a form of shear stress, which is mainly experienced by round shafts used for driving components in circular motion. For torsion to exist, the shaft must have the tendency to twist. The propeller shafts, helicopter drive shafts, torque tubes in flying control systems are some of the systems that experience torsion.

        The following figure shows a propeller shaft being rotated by the engine. The propeller resists this rotation as it has to work against the air to produce thrust, resulting in torsion. Shafts are mainly designed to withstand torsion.