Can you think of any common applications where this can apply?
Assuming the disc is uniform and isotropic (the same in different directions), the hole will expand in the same ratio as the metal. You can see this because the thermal expansion equation
d๐ฟ=๐ฟ๐ผd๐
applies to all lengths associated with the metal, including the circumference of the hole, since the edge of the hole is made out of metal. And if the circumference of the hole expands, so does the diameter.
If you have a disc with different regions that are made of different types of metal, or if the metal that makes up your disc has an anisotropic crystal structure (so that it expands by different factors in different directions), then the analysis is more complicated. But in both cases, I think the hole would still get larger since the overall change in size is still an expansion.
In order to get the hole to shrink, you would need to use a material with a negative thermal expansion coefficient ๐ผ<0ฮฑ<0, which means it gets smaller as the temperature gets higher. In that case the entire disc would shrink as it heats up.
A practical application of this would be with metal shrink fits.
@hardwarefyi have been reading through your (?) forum โ in general have found answers posted by you are correct, but user posted answers are mostly wrong (โฆ>50%)
Anyways, the forum/question collection is mostly interesting, and your comments in particular have been helpful, so I made an account just to reply here and potentially add some value.
Regarding:
โBut in both cases, I think the hole would still get larger since the overall change in size is still an expansion.โ
The exception case would be where the outside material has much lower coefficient of thermal expansion. In worst case, consider material that doesnโt expand at all โ then the expansion of the inner material would be forced to go inwards, making the hole smaller.
Application wise, its actually quite reasonable that the surface of the hole heats first (direct exposure to convection etc.) causing temperature differential between hole surface and rest of material. In this case, I could see hole shrinking (surrounding cold material prevents it from expanding outward) before expanding (surrounding material expands).
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