When elastic deformation occurs, a body recovers its original shape when the applied stress is released. On the contrary, the change in the shape of an object is irreversible when plastic deformation occurs, explains a Iowa State University sponsored website.
Generally, deformation refers to the effect in the change of an object's shape when an exterior force is applied on its surface. In some cases, a change in temperature may also cause deformation. The external force applied on an object may be a torque, tangential or normal to the surface. Depending on the type, size and geometry of the material, and forces applied, a number of deformations may occur. Two most common types of deformation are elastic and plastic deformations. Others include compressive failure, metal fatigue and fracture.
When an external force is applied on an object, the object tends to pull itself apart. This increases the distance among atoms, which attempt to pull themselves towards one another as a way of resisting the stress. When the force is not sufficient to cause a permanent change, the object regains its original shape once the force is removed. This is known as elastic deformation.
Sometimes, a force being applied on a body may be massive, causing a total breakage of bonds among atoms. This may cause a permanent change in the shape of a body. This type of deformation is referred to as plastic deformation.