You are Here: Home >< Physics

# stress strain graph necking watch

1. I know that necking causes a stress strain graph to start to curve but I don't understand how. If stress is force/area and area is the same and force is increasing by 100 grams each time then the stress shouldn't cause it to curve. strain is change in length/length so it should carry on being proportional as the length it stretches increases when more weight is added rather than the extension getting less?
can someone explain what Im getting so confused about?

Thanks
2. Different materials have different stress strain graphs. Concrete has a linear stress strain graph because it only undergoes elastic deformation. Something like copper wires has a linear section when it undergoes elastic deformation, but also has a curved section where it undergoes plastic deformation.
Elastic deformation mean that after it has been extended it can return to it original length
Plastic deformation means that after it has been extended it CANNOT return to its original length
3. (Original post by jonnypdot)
Different materials have different stress strain graphs. Concrete has a linear stress strain graph because it only undergoes elastic deformation. Something like copper wires has a linear section when it undergoes elastic deformation, but also has a curved section where it undergoes plastic deformation.
Elastic deformation mean that after it has been extended it can return to it original length
Plastic deformation means that after it has been extended it CANNOT return to its original length
Oh right thanks.
So when the copper wire undergoes plastic deformation does the change in length increase more than when its undergoing elastic deformation?
4. (Original post by dont)
Oh right thanks.
So when the copper wire undergoes plastic deformation does the change in length increase more than when its undergoing elastic deformation?
yes

### Related university courses

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: November 3, 2015
Today on TSR

### Exam Jam 2018

Join thousands of students this half term

### Solo - A Star Wars Story

Poll

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE