Plasticity is the permanent mode of deformation of a material. When a material is subjected to stress, it undergoes deformation. If the stress is removed, the material returns to its original state, which is known as elastic deformation. However, if the stress is applied beyond a certain limit, the material undergoes plastic deformation, which is permanent and irreversible.

Plastic deformation occurs when the stress applied to a material exceeds its yield strength. At this point, the material begins to deform permanently, and its shape changes. The amount of plastic deformation that a material can undergo before it fails is known as its ductility.

Plastic deformation can occur in many different ways, including stretching, bending, and twisting. The most common form of plastic deformation is known as slip deformation, which occurs when planes of atoms in the material slide past one another. This causes the material to deform permanently, and it can be seen as a change in shape or size.

Twinning deformation is another form of plastic deformation that occurs when a crystal is split into two parts along a plane of atoms. This causes the material to deform permanently, and it can be seen as a change in shape or size.

In conclusion, plasticity is the permanent mode of deformation of a material that occurs when the stress applied to a material exceeds its yield strength. Plastic deformation can occur in many different ways, including slip deformation and twinning deformation.

Plasticity -ability of material to change shape and size permenantly without failure