# Tricksy thermal stress question

1. May 12, 2008

### Vuldoraq

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

A steel rod 0.350 {\rm m} long and an aluminum rod 0.250 {\rm m} long, both with the same diameter, are placed end to end between rigid supports with no initial stress in the rods. The temperature of the rods is now raised by 60.0 {\rm ^\circ C}.

What is the stress in each rod?

Youngs moduli:$$Steel=20*10^{10}, Aluminium= 7*10^{10}$$

Coef. of linear expansion: $$Steel=1.2*10^{-5}, Aluminium=2.4*20^{-5}$$

2. Relevant equations

$$\frac{F}{A}= Y(\frac{\Delta L}{L_{0}}-\alpha \Delta T)$$

3. The attempt at a solution

I am completely flumuxed, I know that that the total length of the two rods doesn't change but how do I find out which rod will expand and which be compressed? Any help getting started would be great.