Compression rate
Introduction
In mechanics, compression is the application of balanced forces inward ("push") to different points of a material or structure, that is, forces without net sum or torque directed to reduce the size of the material or structure in one or more directions.[1] Contrast with tension "Strain (mechanical)") or traction, the application of balanced forces outward ("traction"); and with shear forces, directed to move layers of the material parallel to each other. The compressive strength of materials and structures is an important engineering consideration.
In uniaxial compression, forces are directed along a single direction, so that they act toward decreasing the length of the object along that direction.[2] Compression forces can also be applied in multiple directions; for example inwards along the edges of a plate or across the entire lateral surface of a cylinder "Cylinder (geometry)"), to reduce its area (biaxial compression), or inwards over the entire surface of a body, in order to reduce its volume.
Technically, a material is under a state of compression, at some specific point and in a specific direction , if the normal component of the stress vector "Stress (mechanical)") across a surface with normal direction is directed opposite to . If the stress vector itself is opposite to , the material is said to be under normal compression or pure compressive stress along . In a solid, the amount of compression generally depends on direction, and the material may be under compression in some directions but under tension in others. If the stress vector is purely compressive and has the same magnitude in all directions, the material is said to be under isotropic compression or hydrostatic compression at that point. This is the only type of static compression that liquids and gases can withstand.[3].
In a mechanical longitudinal wave, or compression wave, the medium moves in the direction of the wave, resulting in areas of compression and rarefaction.
Effects
When subjected to compression (or any other type of stress), any material will undergo some deformation, however imperceptible, which causes the average relative positions of its atoms and molecules to change. The deformation may be permanent or may be reversed when the compressive forces disappear. In the latter case, deformation gives rise to reaction forces that oppose the compression forces and can eventually balance them.[4].