William Couture wrote:

> If you heat the middle (containing a hole) of a piece of metal, it will
> expand.  But the rest of the piece isn't getting out of it's way to make
> expansion easy.  This introduces stress in the piece of metal.

Right: "introduces stress". So what does this stress do to the hole? 

This is a normal situation when (gas) welding, isn't it? I don't think
people usually heat the complete sheet up to welding temperature when they
weld a piece to a sheet. So there is then a hot area in the middle,
surrounded by a cooler area. What happens to a hole in the hot area in the
middle? (You probably shouldn't try that with cast iron, but that's a
different story.)

So far even Tony's argument ("'Gadzooks!'") didn't really sound too
scientific about what happens in this situation to a hole. 

Gerhard

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