Definition and Types of Compression
– Compression is the application of inward forces to a material or structure, reducing its size in one or more directions.
– It is contrasted with tension or traction, which applies outward forces, and shearing forces, which displace layers of the material parallel to each other.
– Compression can be uniaxial, acting along one direction, or biaxial, acting in multiple directions.
– A material is under compression if the normal component of the stress vector across a surface is directed opposite to that surface.
– Liquids and gases can bear isotropic compression, affecting their volume.
Effects of Compression
– Every material undergoes deformation when subjected to compression, even if imperceptible.
– Deformation may be permanent or reversible, depending on the material and the compression forces.
– Liquids and gases cannot bear steady uniaxial or biaxial compression but can bear isotropic compression momentarily.
– Different materials exhibit different behaviors under compression, with some expanding or remaining unchanged in certain directions.
– The relation between stress and deformation is a central topic in continuum mechanics.
Uses of Compression
– Compression of solids is important in materials science, physics, and structural engineering.
– Mechanical properties such as compressive strength and modulus of elasticity can be measured through compression.
– Compression machines, ranging from small to large capacities, are used for testing.
– Gases are often stored and shipped in compressed form to save space.
– Compressed liquids are used in hydraulic equipment and fracking.
Compression in Engines
– In internal combustion engines, the explosive mixture is compressed before ignition, improving engine efficiency.
– Compression is a key step in the Otto cycle, where the second stroke compresses the charge drawn into the cylinder.
– In steam engines, compression occurs when the exhaust valve closes before the piston stroke is complete.
– Compression cushions the piston, reducing stresses due to inertia and preventing shocks during the return stroke.
– Compression in engines enhances performance and efficiency.
Related Concepts
– Buckling, a structural failure mode, is related to compression.
– Compression tests are conducted to evaluate container strength and compressive strength of materials.
– Compression members are structural elements designed to withstand compressive forces.
– Longitudinal waves, such as sound waves, involve areas of compression and rarefaction in the medium.
– The strength of materials and their behavior under compression is a subject of study in mechanics. Source: https://en.wikipedia.org/wiki/Compression_(physics)
In mechanics, compression is the application of balanced inward ("pushing") forces to different points on a material or structure, that is, forces with no net sum or torque directed so as to reduce its size in one or more directions. It is contrasted with tension or traction, the application of balanced outward ("pulling") forces; and with shearing forces, directed so as to displace layers of the material parallel to each other. The compressive strength of materials and structures is an important engineering consideration.
In uniaxial compression, the forces are directed along one direction only, so that they act towards decreasing the object's length along that direction. The compressive forces may also be applied in multiple directions; for example inwards along the edges of a plate or all over the side surface of a cylinder, so as to reduce its area (biaxial compression), or inwards over the entire surface of a body, so as to reduce its volume.
Technically, a material is under a state of compression, at some specific point and along a specific direction , if the normal component of the stress vector 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 the direction , and the material may be under compression along some directions but under traction along others. If the stress vector is purely compressive and has the same magnitude for all directions, the material is said to be under isotropic compression, hydrostatic compression, or bulk compression. This is the only type of static compression that liquids and gases can bear. It affects the volume of the material, as quantified by the bulk modulus and the volumetric strain.
The inverse process of compression is called decompression, dilation, or expansion, in which the object enlarges or increases in volume.
In a mechanical wave which is longitudinal, the medium is displaced in the wave's direction, resulting in areas of compression and rarefaction.
