Torsion (mechanics)

Torsion could be defined as strain[3][4] or angular deformation[5], and is measured by the angle a chosen section is rotated from its equilibrium position[6].

The resulting stress (torsional shear stress) is expressed in either the pascal (Pa), an SI unit for newtons per square metre, or in pounds per square inch (psi) while torque is expressed in newton metres (N·m) or foot-pound force (ft·lbf).

In non-circular cross-sections, twisting is accompanied by a distortion called warping, in which transverse sections do not remain plane.

The angle of twist can be found by using: Calculation of the steam turbine shaft radius for a turboset: Assumptions: The angular frequency can be calculated with the following formula: The torque carried by the shaft is related to the power by the following equation: The angular frequency is therefore 314.16 rad/s and the torque 3.1831 × 106 N·m.

If one adds a factor of safety of 5 and re-calculates the radius with the maximum stress equal to the yield stress/5, the result is a diameter of 69 cm, the approximate size of a turboset shaft in a nuclear power plant.