Thermal mismatch
Thermal mismatch
(OP)
I'm trying to design a section of aircraft structure that bolts an aluminium panel (secondary structure) to a carbon composite panel (primary structure). There is the need to account for extreme hot & cold temperatures and this is generating large thermal stresses and bolt loads dur to the thermal mismatch. Any ideas on how best to deal with this? I thought about slotted holes to allow for some expansion in the critial direction. Is the use of slotted holes acceptable?
RE: Thermal mismatch
RE: Thermal mismatch
I wonder if the olde Boeing design manual has any insights. If it is that critical to the design, I'm sure smarter people than us have already solved this with clever design approaches.
another day in paradise, or is paradise one day closer ?
RE: Thermal mismatch
Secondary structure... what is the Joint configuration? Fasteners?
WHY does the secondary structure have-to-be aluminum-to-graphite? Titanium or even a composite panel [S-glass/epoxy] to carbon-epoxy seems more balanced.
What is the isolation interface between carbon [graphite] and aluminum... corrosion potential is gorilla-in-the-closet!
Real-world thermal design range? Example: -65F to 250F... or....??
I expect that 7xxx alloys are unsuitable much above 225F; 2024-T81 would be unsuitable above ~300F; and only 2219-T6 would be suitable from 325F to [maybe] 375F or 400F [short exposure]. IF temp range is really high... then only special corrosion protective primer-hybrid-blends will survive-long-term above 350F.
Is the problem with high thermal-induced stress [a] axial or [b] biaxial in the aluminum? IF the aluminum part had built-in expansion 'wrinkles'... or keyhole slots [long-thin slots with a large diameter hole at the end/base of each slot]… with fasteners installed thru the edge 'ands' or 'flat-lands' into the composite... MIGHT be a way to relieve/soften stresses in the aluminum fastening along the composite edge. expansion contraction would then be a long-term issue.
Regards, Wil Taylor
o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation,Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", Homebuiltairplanes.com forum]
RE: Thermal mismatch
If you use slotted holes they should be in the aluminum part, not the composite part. But likely not needed.
RE: Thermal mismatch
Or try something like a wiggle plate, similar to what wktaylor described:
https://www.atsmro.com/wp-content/uploads/2019/09/...
Good point raised earlier regarding integrity of fay surface sealant. If you rely on clearance holes and there is definite thermally induced strains, then the seal will be broken and the aluminium will corrode.
RE: Thermal mismatch
TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm
RE: Thermal mismatch
another day in paradise, or is paradise one day closer ?
RE: Thermal mismatch
look at how plate glass in building is mechanically secured to metal structure. I'm looking at a cool spider looking thing in the corner of my office windows.