Stresses may be divided into the following five classes according to the action of the force producing them:

(a) Tension (pulling stress) usually called tensile stress.

(6) Compression (crushing stress) usually called compressive stress.

(c) Shearing (cutting stress).

(d) Torsion (twisting stress).

(e) Flexure (bending stress).

Tension, or pulling stress, is the force that overcomes external forces that tend to stretch a body. A rope or wire supporting a load is an example of tensile stress. The rope or wire is subjected to a tensile stress of the weight of the load.

Compression, or crushing stress, is produced when external forms act so as to compress a volume or any supporting body. When an engine rests upon rails, the rails are subjected to the compressive stress of the weight of the engine.

Shearing, or cutting stress, is produced when forces tend to cause the particles of one section to slide over the section of an adjacent body. When a bolt is in tension the head of the bolt is subjected to a shearing stress tending to strip the head from the shank of the bolt.

Torsion, or twisting stress, is produced when forces tend to twist. A rotating shaft is obliged to resist a twisting force.

Flexure, or bending stress, is produced when forces tend to bend. A floor timber in a house has to resist the bending force that tends to break it.