Axial resistance test
Introduction
The compressive stress is the result of the tensions or pressures that exist within a deformable solid or continuous medium, characterized by the fact that it tends to reduce the volume of the body, and to shorten the body in a certain direction (Poisson's ratio).
In sufficiently slender structural parts, compression stresses can also produce denting or buckling.
In general, when a material is subjected to a set of forces, bending, shearing or torsion occurs; all of these efforts lead to the appearance of both tensile and compressive stresses. Although in engineering a distinction is made between compressive (axial) stress and compressive stresses.
In a mechanical prism, the compression stress can simply be the resultant force that acts on a certain section transverse to the barycentric axis of said prism, which has the effect of shortening the piece in the direction of the barycentric axis. Prismatic pieces subjected to a considerable compressive stress are susceptible to flexural buckling, so their correct sizing requires examining this type of geometric nonlinearity.
Compression test
The tests carried out to measure the compressive stress are contrary to those applied to the tensile stress, with respect to the direction of the applied force. It has several limitations:
• - Difficulty of applying a concentric or axial load, without buckling appearing.
• - A specimen with a circular section is preferable to other shapes.
The test is carried out on materials:
• - Hard.
• - Semi-hard.
• - Soft.
Compression stresses in elongated pieces
In a non-slender prismatic piece, which is not susceptible to buckling, subjected to uniform uniaxial compression, formed by a linear elastic material, the tension, unit shortening and displacements are related to the total compression stress through the following expressions:
Where:.