Plastic deformation is the permanent change in shape of a material when it's subjected to a stress beyond its elastic limit. Unlike elastic deformation (which is reversible), plastic deformation does not go away when the stress is removed.
Happens in metals, polymers, and some ceramics.
It’s how metals bend instead of breaking.
Caused by the movement of defects in the material's atomic structure—like dislocations.
🧱 Dislocations
Dislocations are defects in the crystal structure of a material that allow it to deform more easily. Think of them as "slips" or "extra planes of atoms" in a normally perfect atomic arrangement.
There are two main types:
Edge Dislocation
An extra half-plane of atoms is inserted in a crystal.
Moves like a ripple through the crystal when force is applied.
Screw Dislocation
The crystal layers spiral around a central point like a screw thread.
These dislocations move through the crystal when stress is applied, allowing atoms to shift incrementally, which is far easier than breaking all atomic bonds at once.
🔄 How They Relate
Dislocations are the mechanism behind most plastic deformation in crystalline solids. Instead of needing enough energy to break all atomic bonds in a plane at once (which would require a ton of force), only a few bonds at a time move to dislocations, making metals ductile and formable.