Question

What is plasticity?

Answer 1

Solids are composed of atoms and molecules. They are bonded together by the interatomic or intermolecular forces. These forces are the strongest in solids. Hence solids have a definite shape and size. When an external force deforms the shape of a body there will be a restoring force developed in the body opposing the deformation.

Complete step by step solution:
In solids, when we apply an external force the shape of the material gets deformed. There will be an internal restoring force developed inside the solid that opposes the change in shape, size and volume of the solid material. This force is known as the stress. If a body gets deformed when an external force is applied and if it regains its original shape after the removal of the deforming force, then the material is said to be elastic material. If a body gets permanently deformed when an external force is applied, then the body is said to be plastic. This property of a material to change its shape, size or volume when a force is applied is called plasticity. In many metal forming processes and geological processes the plastic deformation takes place.

Note:
The plastic behaviour of a material corresponds to the ultimate tensile strength of the material. If we apply a force beyond the plastic limit of a material, the material will break. This point is called the fracture point or the breaking point. If the plastic point and breaking point of a material is far then the material is ductile. If they are close then the material is brittle.