Strain
1. Strain is the amount of deformation experienced by the body in the direction of force applied, divided by the initial dimensions of the body.
2. Strain, in physical sciences and engineering, number that describes relative deformation or change in shape and size of elastic, plastic, and fluid materials under applied forces.
The deformation, expressed by strain, arises throughout the material as the particles (molecules, atoms, ions) of which the material is composed are slightly displaced from their normal position.
Strains may be divided into normal strains and shear strains on the basis of the forces that cause the deformation. A normal strain is caused by forces perpendicular to planes or cross-sectional areas of the material, such as in a volume that is under pressure on all sides or in a rod that is pulled or compressed lengthwise.
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