In the calculation of structures and engineering, traction is the internal force to which a body is subjected by the application of two forces that act in opposite directions, and tend to stretch it.

Logically, it is considered that the tensions that any section has perpendicular to said forces are normal to that section, and have opposite directions to the forces that try to lengthen the body.

A body subjected to a tensile stress suffers positive deformations (stretching) in certain directions due to the traction. However, stretching in certain directions is generally accompanied by shortening in transverse directions; Thus, if in a mechanical prism, traction produces an elongation on the "X" axis, which in turn produces a shrinkage on the "Y" and "Z" axes. This shrinkage is proportional to the Poisson's ratio (ν):

When it comes to solid bodies, the deformations can be stretching: in this case, the body has exceeded its yield point and behaves plastically, so that after the tensile stress ceases, the elongation is maintained; If the deformations are not permanent, the body is said to be elastic, so that, when the tensile stress disappears, it recovers its original length.

The relationship between the traction acting on a body and the deformations it produces is usually represented graphically using a Cartesian axis diagram that illustrates the process and provides information about the behavior of the body in question.

As a comparative value of the characteristic resistance of many materials, such as steel or wood, the value of the failure stress, or tensile exhaustion, is used, that is, the ratio between the maximum load that has caused the elastic failure of the material by tensile and the surface of its initial cross section.

There are many materials that are subjected to traction in various mechanical processes. Of special interest are those used in architectural or engineering works, such as rocks, wood, concrete, steel, various metals, etc.