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Shearing

 

1. mechanical removal of the sheep's fleece. A traumatic event in the sheep's annual calendar. A time for the transmission of diseases between sheep, e.g. mycotic dermatitis, caseous lymphadenitis, infection with environmental infections, e.g. gas gangrene, tetanus, and for exposure to inclement weather without the protection of a fleece.
chemical shearing, the shedding of the fleece after administration of a chemical agent, is in the very early stages of exploration. Automatic shearing done by robots is perhaps a little closer. Breeding of sheep which shed their fleece annually is always a good cause for a research program. The Wiltshire horned breed does this to a varying degree.
2. a type of injury. See shearing injuries (below).

  • s. board — open area in a shearing shed on which the sheep are restrained while they are shorn.
  • s. hypothermia — see hypothermia.
  • s. injuries — 1. injuries inflicted to a sheep during shearing and by the shearing machine. Lacerations are frequent but cause little damage if they do not become infected. They appear to cause no discomfort and heal very quickly. The serious injuries are the removal of teats in ewes, damage to the prepuce and removal of the tip of the vulva. The last two lead to deviation of the stream of urine, fouling of the nearby fleece and increased risk of blowfly strike.
  • — 2. injuries in which there is the application of a shearing force tending to cause local deformity or diplacement; usually involve the carpus or tarsus in small animals hit by motor vehicles. There is extensive loss of soft tissues and bone, with exposure of the joint.
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Wikipedia: Shearing (physics)
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Shearing in continuum mechanics refers to the occurrence of a shear strain, which is a deformation of a material substance in which parallel internal surfaces slide past one another. It is induced by a shear stress in the material. Shear strain is distinguished from volumetric strain, the change in a material's volume in response to stress.

Often, the verb shearing refers more specifically to a mechanical process that causes a plastic shear strain in a material, rather than causing a merely elastic one. A plastic shear strain is a continuous (non-fracturing) deformation that is irreversible, such that the material does not recover its original shape. It occurs when the material is yielding. The process of shearing a material may induce a volumetric strain along with the shear strain. In soil mechanics, the volumetric strain associated with shearing is known as Reynolds' dilation if it increases the volume, or compaction if it decreases the volume.

The shear centre is an imaginary point on a section, where a shear force can be applied without inducing any torsion. In general, the shear center is not the centroid. For cross-sectional areas having one axis of symmetry, the shear center is located on the axis of symmetry. For those having two axes of symmetry, the shear center lies on the centroid of the cross-section.

In some materials such as metals, plastics, or granular materials like sand or soils, the shearing motion rapidly localizes into a narrow band, known as a shear band. In that case, all the sliding occurs within the band while the blocks of material on either side of the band simply slide past one another without internal deformation. A special case of shear localization occurs in brittle materials when they fracture along a narrow band. Then, all subsequent shearing occurs within the fracture. Plate tectonics, where the plates of the Earth's crust slide along fracture zones, is an example of this.

Shearing in soil mechanics is measured with a triaxial shear test or a direct shear test.

See also

References

  • Terzaghi, K., 1943, Theoretical Soil Mechanics, John Wiley and Sons, New York 123
  • Popov, E., 1968, Introduction to mechanics of solids, Prentice-Hall, Inc., New Jersey

 
 

 

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Veterinary Dictionary. Saunders Comprehensive Veterinary Dictionary 3rd Edition. Copyright © 2007 by D.C. Blood, V.P. Studdert and C.C. Gay, Elsevier. All rights reserved.  Read more
Wikipedia. This article is licensed under the Creative Commons Attribution/Share-Alike License. It uses material from the Wikipedia article "Shearing (physics)" Read more