Polymeric Materials OCR Physics

Can anyone help me on the properties of polymeric materials and their stress-strain and force-extension graphs. Im fine with ductile and brittle but not at all with polymeric materials.

Reply 1

Zaros

Original post by Higgzy

Can anyone help me on the properties of polymeric materials and their stress-strain and force-extension graphs. Im fine with ductile and brittle but not at all with polymeric materials.

Sadly I can't give a demonstration of this, because it would probably be easier for you to understand if you could see. However, if you go get yourself a plastic bag, and then try and stretch it, you're going to experience what a polymeric material is like. If you begin to stretch the plastic you will find that at the start it's very hard to stretch, but once you reach a certain point it becomes very easy to stretch and then goes back to being hard to stretch, just before it snaps.
So, lets just go over why this happens so you can understand why it happens. A polymeric material is a name given to a material that we make out of carbon chains, and these are generally long and twisted into one another. So when you stretch the starting resistance is these chains, not wanting to unravel themselves. However once they begin to line up, it becomes very easy to pull them as they slide into straighter chains. Finally before snapping it gets hard as the forces between the molecules tries to keep them together.
In terms of stress and strain, look at the stress-strain curve and you'll see just what I described. It begins with a very high stress to little strain, then it dips and then increases until it snaps.

I really hope that helped :smile: