Contact Conductance in Riveted Joint

[MrRogers1987]

I'm trying to work through a thought experiment with a colleague about how to estimate the heat transfer across a riveted joint. The application will be in a vacuum, so there's no interstitial fluid between the joined members to help with conduction. Thus you are highly reliant on surface finish and contact pressure basically causing surface imperfections to yield and increase contact between the joined members. In my industry bolted joints are much more common for the type of connection being examined here, but I don't feel we should treat this the same way thermally. I am not overly familiar with riveted joints though and am struggling to convince myself what the primary mechanism for heat flow will be and what can be neglected.
[ul]
[li]For example, it's not immediately intuitive to me whether the amount of contact pressure from a riveted joint is comparable to a properly preloaded fastener. My understanding is that rivets are primarily for carry load in shear, and the tensile capability is basically just the rivet head. This makes me think the joint isn't under as much compression as a bolted joint, but again I'm not very familiar with riveted installations.[/li]

[li]Can anyone point to a reference which discusses contact pressure between riveted members?[/li]​

[li]Is there local deformation in the joined members from the riveting process that reduces the contact area in the vicinity? Or does it work in the favor of compressing the members together?[/li]
[li]Assuming the contact force is not significant, is it reasonable to assume that the majority of the heat transfer is through the shank of the rivet and not through contact of the joined members (basically opposite of a bolted joint)?[/li]
[/ul]

Any other insight or considerations that might be helpful in working through this thought experiment is welcome as well!

 

[1503-44]

Fluid does not help. Heat transfer would be via convection, not conduction, and is much less efficient. Direct Contact is via conduction. That's what you want.

A rivited joint is probably going to be pretty tight and you should get heat transfer through the entire contact area of the surfaces, not just through the rivet itself. If you get deformation of the surfaces that reduces heat transfer, your joint has probably failed and its already flying off in two directions.

--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."

 

[MrRogers1987]

Having an interstitial fluid (or gas) to "fill in" the microscopic imperfections helps aid the conduction. We're not talking about a gap between plates here where convection would take place, but conduction through the fluid. I can assure you that relative to NO fluid (i.e. in a perfect vacuum) there is a noticeable difference to having some sort of gas or other interstitial fluid.

I agree that assuming heat transfer only through the rivet body is probably underrepresenting the total conduction across the interface. Quantifying what the contact pressure is for a riveted joint is what I'm unsure about though. For a preloaded bolt it's straightforward since the clamping force can be controlled to a relatively good degree. Can you make a similar estimate of rivet clamping force from the setting process if you know things like rivet type, size, and plate thickness? I would assume it is a less controlled process so there would need to be a pretty large uncertainty around whatever nominal estimate you could make.

 

[1503-44]

OK. Yes obviously a fluid in a gap is better for conduction than an open gap having zero conduction.

I would suppose that some rivit type installations could offer some control possibilities, or you could derive some parameters for it, but I don't know enough about that.



--Einstein gave the same test to students every year. When asked why he would do something like that, "Because the answers had changed."