What Is Plastic Deformation In Metals?

Deformation of materials can be defined as macroscopic changes to the size and shape of materials under the effect of mechanical loading, thermal loading or phase transformation, etc.

From a mechanical point of view, it is possible to classify deformation into two as elastic and plastic deformation.

Elastic & Plastic Deformation

When the external stress does not exceed the yield strength of the material, the material undergoes elastic deformation, which is nonpermanent, meaning, as the applied stress is removed, the material tends to turn back to its original size and shape.

In the elastic region, stress and strain increase proportionally to each other by perfectly following Hook’s Law. As the applied stress increases above the yield point, the plastic deformation stage initiates in which, the material deforms much quicker, and permanently.

Within the plastic region there are both elastic and plastic deformation exist. Figure 1 represents a typical stress-strain diagram of a metal. Here, point A represent proportionality limit at which linear nature of the graph disappears, and point B represents yield strength (elasticity limit) of the material. Beyond point B is called as plastic region in which, strain is permanent.

During plastic deformation, some cracks are formed and propagate until the material fractures completely.