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The amount of stretch or compression along material line elements or fibers is the normal strain, and the amount of distortion associated with the sliding of plane layers over each other is the shear strain, within a deforming body. [2] This could be applied by elongation, shortening, or volume changes, or angular distortion. [3]
The second type is compression. This occurs when rocks are squeezed together causing them to fold or fracture. While confining stress and compression stress both deal with rocks in a state of compression, the difference lies in that confining stress is a vertical stress, making it influenced by gravity.
In areas of high crustal stretching, individual extensional faults may become rotated to too low a dip to remain active and a new set of faults may be generated. [3] Large displacements may juxtapose syntectonic sediments against metamorphic rocks of the mid to lower crust and such structures are called detachment faults.
In geology, the term "tension" refers to a stress which stretches rocks in two opposite directions. The rocks become longer in a lateral direction and thinner in a vertical direction. One important result of tensile stress is jointing in rocks.
In geology, the term compression refers to a set of stresses directed toward the center of a rock mass. Compressive strength refers to the maximum amount of compressive stress that can be applied to a material before failure occurs.
When an object is subjected to a force in a single direction (referred to as a uniaxial compression), the compressive stress is determined by dividing the applied force by the cross-sectional area of the object. [1] Consequently, compressive stress is expressed in units of force per unit area. Axial Stress
We now consider an incompressible material under uniaxial tension, with the stretch ratio given as =, where is the stretched length and is the original unstretched length. The pressure p {\displaystyle p} is determined from incompressibility and boundary condition σ 2 = σ 3 = 0 {\displaystyle \sigma _{2}=\sigma _{3}=0} , yielding:
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 ...