[EvaH (OP)]

V wants to know:

I am confused between inelasticity and plasticity of metals. Is there a clear cut demarcation between inelasticity and plasticity of metals? Both seems to be same. None of the internet articles give a clear and convincing answer. Please clarify the difference. Thank you.

What do you think?

[Origin]

Plasticity is approximately the same as ductile.  A sufficient force applied to a ductile or plastic body will permanently deform the body.  Normal window glass at room temperature is brittle and not ductile (plastic).  If you bend a sheet of glass and then stop bending it, it will return to its previous shape, it will not stay deformed.  If you bend it too far it will break, it won't ever get to a point where it will stay bent.
So bottom line plasticity is a permanent deformation of a body from a stress.

All macro materials are inelastic.  A force applied to an inelastic body will deform the body but not necessarily permanently deform the body.  Think of 2 billiard balls hitting each other, on a microscopic scale the crystal lattice of the balls deform and then after the collision immediately return to their previous shape.
An inelastic body will deform under stress, but the deformation does not have to be permanent.  .

[evan_au]

In common usage, "elastic" and "plastic" conjure up images of similar (hydrocarbon-based) materials.

Take an "elastic band":
- If you stretch it a bit and release it, it will immediately bounce back to the original size
- If you stretch it a lot, it will permanently deform, and won't return to its original size.
- If you stretch it too much, it will break

A similar pattern applies to many kinds of materials, whether they be glass, metals, or hydrocarbon-based "plastics"
- Different materials have different properties in regards to how much you can stretch them before they permanently deform or fracture.
- These properties change with temperature
- One of the problems with the Titanic was that, in water below 0C, the steel alloy they used became brittle, so it fractured rather than deformed.

See the graph here: https://en.wikipedia.org/wiki/Deformation_(engineering)#Elastic_deformation