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Allowing Surfaces to Slip under Thermal Expansion

Allowing Surfaces to Slip under Thermal Expansion

Allowing Surfaces to Slip under Thermal Expansion

(OP)
We have a system that has a polished aluminium surface pressed onto a smooth copper coated ceramic one.
Because of differential thermal expansion the aluminium will spread radially and pull the ceramic into tension.
We think we need to have a low enough coefficient of friction between the two surfaces to allow them to slip before it fractures the ceramic, but are struggling to quantify it.
The problem is that the two materials are being compressed together at about 4 N/mm2 (600 psi) pressure, to doing full scale testing is impractical. Testing so far seems to be suggesting we need a lubricant (we have tried oil).
Is our only practical option to do small area testing, or are there any other options anyone can suggest?

We are wondering about Rhodium plating or similar dry system instead of a fluid lubricant, which would better suit other requirements.

On a related subject, would a test at a lower pressure be valid, or do real world effects such as asperity crushing make this invalid?

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