The shafts are usually cylindrical in section, solid or hollow. They are made of mild steel, alloy steel and copper alloys. Shaft may be subjected to the following loads:
1. Torsional load
2. Bending load
3. Axial load
4. Combination of above three loads.
The shaft are designed on the basis of strength and rigidity. Shafts are also used to transmit power from a motor to a pump or compressor, from an engine or turbine to a generator, and from an engine to axle in automobiles. During power transmission, the shaft is subjected to torque which causes twist of the shaft.
A shaft needs to be designed that the excessive twist is avoided and the induced shear stress is within prescribed limits.