Press / Interference Fit of Composite Cylinder

Rubber is essentially an incompressible material, so its likely to get complicated.

It will be best to use FEA for that. Many programs support interference fit in contact (parts are modeled with initial penetration and the software automatically brings the surfaces to contact, while generating proper stresses and strains) and you can account for all the nonlinearities.

FEA for rubber bushings is about as accurate as manual methods (but it is good for identifying stress raisers and the effect of bonding between the rubber and the metal). SWComposites has it, Poisson's ratio for rubbers is 0.5 so you are looking at a constant volume solution, the details of which will vary depending on how the rubber is constrained. A better description of the actual problem is probably needed.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

Depending on the ratio of engagement to diameter with rubber one will get various results. For small ratios, <~2, of depth to diameter, the rubber will displace axially. I would expect by the time the part reaches a ratio of 5 that the very low compressibility of rubber will convert the problem to a hoop-stress problem and it will take a heavy wall tube to develop compression in the pin in the middle.

I have seen and tried a demo where a rubber plug is trapped in a heavy wall cylinder and a close-fit pin is set onto that plug. Hitting that pin with a hammer was no different than if the pin was on an anvil, no deflection at all.

The big unknown is the coefficient of friction at the rubber metal interface which will vary with cleanliness, humidity and the insertion force.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

Would compression set result in a loss of interference over time as well?

I take it that the rubber is in the bushing before it is press fit into the other member?
How much interference was in the original fit of the rubber?
Just run numbers for the metal parts, and then go back and add od compression to the rubber based on those values.
It would help if you knew the real properties for your rubber, they very a lot.

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P.E. Metallurgy, consulting work welcomed

Almost all the bushings I am familiar with are bonded, otherwise grit gets between the rubber and the metal. Most are sized, that is the outer metal is crushed after the rubber is bonded in place, to provide a uniform compression of the rubber, for durability - rubber in tension is not going to last long. So far as I am aware creep is not an issue with the compounds/designs we use, but I can imagine natural rubbers and the like would creep as there is no carbon to lock the molecular chains together.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376