# Some help on thermal expansion

1. Feb 10, 2012

### heloo

Hi, I have been asked to determine the stress in a bar which has a diameter of 50mm when the temperature changes from 20 C to 50C. That's the first part.

Secondly, I need to then answer whether or not the stress will be sufficient enough to raise a constraining load of 40 tonnes.

Young's Modulus is 70Gpa.

I think i need to use (1+alpha delta T), to work out the change in length. But that's as far as i've got.

Can anyone give me a pointer in the right direction as i totally confused myself.

Thanks
1. The problem statement, all variables and given/known data
Yes

2. Relevant equations
Unsure of what equations are relevant

3. The attempt at a solution
None

Last edited: Feb 10, 2012
2. Feb 11, 2012

### LawrenceC

OK, you have the equation to determine the change in length were it not constrained. So how much force does it take to compress it back to its original length? Do you know what equations to use?

3. Feb 11, 2012

### heloo

I am unsure of what equations to use, i assume i need to work out the thermal expansion but i don't know how to calculate how much force is needed to force it back to its original length.

4. Feb 11, 2012

### LawrenceC

You should have seen the following equation by now in your studies:

S = e * E

where S is stress, e is strain, and E is Young's Modulus. Given the definition of stress as force per unit area, you can solve it from this point onward.