I'm working on a long mandrel for a customer request, the mandrel needs to be 3" X 6" X 96" long. We'll be doing a composite wrap with a subsequent gellation at 177°C (350°F). We have a total tolerance of .010" for the final product, so the CTE of the mandrel has to be taken into account to hold the tolerance.
Mandrel material is 6061 Al, CTE of 1.4 X 10-5 in/in°F with wall thicknesses of .093" and .183" respectively and a Delta T of 280°F.

So the question is whether the thermal growth of the rectangular section is relative to the section lengths (6" and 3") or the wall thicknesses.
Calculated relative to the section lengths, I'm getting a number on the order of 0.0235" for the 6" section and (obviously) half of that for the 3" section. That number just doesn't feel right for a 280°F change.

Generally speaking, the CTE, since its a bulk property, should cause the profile to change equally changing the internal as well as the external dimensions.

I'd just like some confirmation that my approach isn't flawed.

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