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In a single crystal of many metals, the main mechanism of plastic deformation is simple shear parallel to preferred planes and directions, which at ordinary temperatures coincides with those of the highest atomic density. Slip is initiated along a particular plane and in a given direction when the associated component of the shear stress attains a critical value under increasing external load. The amount of plastic deformation in a single crystal is specified by the glide strain, which is the relative displacement of two parallel slip planes at a unit distance apart. When there are several possible slip directions in a crystal lattice, the displacement of any point in the crystal due to simultaneous shears in the appropriate directions can be found from simple geometry. The mechanism of slip-induced plasticity in single crystals, governed by the glide motion of dislocations along corresponding slip planes, has been the subject of numerous investigations in the past.