Metals and alloys SLIP
Metal plastic deformation is consistent with the maximum shear stress along the direction of the plane of the way close-packed atoms to achieve. Thus, in polycrystalline metals, we can think there must be some crystals consistent with the direction of maximum shear stress of close-packed atomic planes. Deformation from here, once hardened, so that rotation of the crystal to produce original position on the further movement difficult to move in the other position is relatively easy to slip the metal is so deformed.
Slip line theory, the general theory of rigid-plastic body of the same sex in a non-uniform in the plane strain. It must repeat noted that the elastic deformation of this ideal material is zero, if it has undergone plastic flow, will continue to flow without work hardening. It should be stressed again, SLIP only valid plane strain problem. In the case of stress and plane strain rate is in a plane, regardless of the third coordinate axis.