Plastic deformation and elastic deformation
Any object will deform under the external force. When the deformation does not exceed a certain limit, the deformation energy disappears after the external force is removed. This deformation is called elastic deformation. If the external force is large, when its action stops, the deformation caused does not completely disappear, and there is a residual deformation called plastic deformation.
Solids are affected by external forces to change the relative position between the points. When the external force is removed, the solids recover the "elastic deformation" of the original state. If the external force is removed and it cannot be restored to its original shape, it is called "paranormal deformation." Because of the different force conditions of the object, within the elastic limit, there are four basic types of elastic deformation: stretching and compression deformation; shear; bending deformation and torsional deformation.