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Dimpled fastener design allowables

Dimpled fastener design allowables

Dimpled fastener design allowables

(OP)
Hi, I am working on a project using a countersunk fastener and dimpled .020 sheet (CP70 titanium) fastened to 7075 Aluminum. Struggling to find an industry standard on how to calculate the design allowable for sucjh a joint. We are using a 130 degree countersin with Hi-Lite pins.
Any help in finding an 'approved/recognized' methodology for this appreciated.

RE: Dimpled fastener design allowables

For spacecraft engineering? I'm pretty sure dimpled fastener installs are prohibited for spacecraft.

YOU will have to test and develop Your own MMPDS-equivalent allowables.

NOTE.
I know with ~99% certainty that 130-Deg dimples [double-dimples or dimples-into-countersinks] 'mechanical allowables' [~=MMPDS] have NOT been characterized.
I've never heard of dimpling Titanium sheet... unsure how You would even do it 'consistently' for a shallow 130-Dimple... and get a clean-round hole. VERY HOT and enlarge the hole on install????

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: Dimpled fastener design allowables

Agree with Wil, you are very unlikely to find industry data or a method to calculate joint strength for that configuration. You will need to conduct specific joint tests for your configuration.

RE: Dimpled fastener design allowables

ditto, this is such an old technology ... doesn't mean it's "wrong" ... it can be an effective way of joining thin sheet.

you may find some data in old Mil Handbook 5 ... I seem to remember some tables there.

A suggestion ... you are almost certainly going to limited by sheet failures, so maybe use rivets (lighter) ?

Have you considered welding ? spot or line ??

another day in paradise, or is paradise one day closer ?

RE: Dimpled fastener design allowables

Based on a previous conversation on Eng-Tips:

https://www.eng-tips.com/viewthread.cfm?qid=496518

Consider using chemically-milled sheets so that you can fully countersink at the fasteners but still maintain thin panels between fastener rows.

RE: Dimpled fastener design allowables

that'd still add mass.

why CSK ? why not protruding head ? Even if covered ...
1) push fastener through the covering layer, or
2) recess (or thru-hole) in the covering layer (to clear the head)

another day in paradise, or is paradise one day closer ?

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