this presentation we will define what torque and torsion are and
we will derive the theory of torsion of circular shafts. Implications
of torsion theory to the failure of materials is also discussed.
Torsion refers to the twisting of a shaft loaded by torque, or twisting
couples. For example, in the generation of electricity shafts
carry torque from the turbine to the generator. An example of torsional
loading is shown here. In this example we load the shaft by two
equal and opposite forces acting on a bar perpendicular to the shaft.
The moment generated by these forces is sometimes called a couple.
This type of loading is shown in the figure. Each of the two forces
tend to twist the shaft about its longitudinal axis. The magnitude
of the moment due to this couple is given by P times d, where,
P is the applied force and d is the distance between
the lines of action of the forces. This twisting couple is also
called the Torque or Twisting Moment.