Thermal Expansion on the Inside

[StressGuy]

Alright, I need a pointer to a resource to help explain something that I learned a while back.

If you look at a cross section of a pipe (or it could be a disc with a hole in the middle). Now, the metal heats up. Naturally, the OD gets bigger. But, so does the ID. The hole on the inside won't get smaller.

I learned this several years ago, but I don't remember the exact explanation. Do any of y'all have a reference that I can use to explain this phenomenon to someone else?

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.

 

[StressGuy]

Well, looks like this is better documented than I remember. I was able to find a few sites on my own, so I thought I'd share:

http://physics.uwstout.edu/StatStr/Strength/Stress/strs38.htm

http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/thexp2.html#c1

http://www.physics.umd.edu/lecdem/services/demos/demosi1/i1-11.htm

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.

 

[25362]

The simplest explanation I remember from highschool days was that thermal linear expansion obliges also the inner perimeter to elongate. This means the hole should get a larger diameter.

 

[IRstuff]

Sure, that makes sense.

If the coefficient of linear expansion is 10^-5, then for a 1 inch diameter tube with 0.1 inch thickness, a 100º temperature change results in 0.0001 inch thickness change, but a 0.0016 inch change in circumference, resulting in a 0.0005 inch increase in diameter, trumping the thickness change.

TTFN

 

[25362]

To IRstuff, wouldn't it be better to apply the linear coefficient to the external perimeter as well ? Thus, the thickness would also increase. Do you agree ?