Pull-Thru Strength of Rivets in Al Sheet

[GrimesFrank]

Pull-Thru Strength of Rivets in Al Sheet
I'm looking for help on this subject I originally posted in the Fastener Forum. I'm thinking that Aeros deal with rivets and membranes enough to help me. Please prove me right ;P

 

[rb1957]

sounds like you're asking for the tension strength of a rivet joint ... McCombs wrote a "Supplement to Bruhn" which has a table ... what materials are we talking about ?

 

[GrimesFrank]

Rivet = 2024-T4 / .312dia shoulder / .187dia shank
Sheet = 5083-H32 / 0.12" thick

I want to calculate the force required to pull the backing through the sheet if pulling on the head.

Today is gone. Today was fun.
Tomorrow is another one.
Every day, from here to there,
funny things are everywhere. ~'Dr.' Theodor Geisel

 

[40818]

GrimesFrank.

0.12 thick is unlikely to develop membrane effects unless the panel dimensions are pretty large.
I have test data somewhere for rivet tension allowables. 191 lbf and 500 lbf come to mind for 1/8" and 5/32" aluminium rivets in 2024 sheet cant remember 3/16". You weren't keen on my quick shear out formualae in the other forum, but if your talking about a rivet in tension it will always go before the sheet, unless the joint is designed wrong. The effect you described earlier about local bending of the sheet until the hole opens up to allow the rivet to pull through wont happen that easily, especially not 0.12" thick.
In effect a combination of shear-out acting onto the sheet combined with the inability of the sheet resist the local bending causes a localised bending field (kinda akin to a funnel) to develop around an individual rivet. If the head is strong enough then it either tears through the sheet due to localised plasticity opening up cracks which ease the passage through, due to local load imbalances teh head tends to dig into one area of the sheet and this is the portion where very high contact stresses cause localised shearing through the sheet. If your still unsure just ask Airbus about the problems they had with all fastener heads on the A400 wing. Countersunk fasteners behave slightly different.

 

[rb1957]

a 3/16" AD (2117) protruding head rivet is good for about 800 lbs tension. in our biz we have to keep 2024 (DD) rivets in an icebox before shooting. if we do that they're good for 1/3 more.

that's the rivet, the sheet would be good for its Fsu* the preimeter > the shank < the head ! * thickness ...

 

[GrimesFrank]

40818,
Sorry if I was short earlier....I really need any help.

I don't know if the joint is designed wrong. The rivet pins a 14 Ga 302SS wire with a loop to 0.12 thick aluminum. If we yank on the wire what fails?

The wire fails at ~905 lb. I was hoping to prove the rivet pops out of the sheet well before then. Yet it looks like, according to rb1957, the rivet fails near that range anyway.

I was treating the sheet as a flat plate with a hole and calculating load required to locally yield the hole edge material. Doing that I was getting 905 lb. My gut was telling me this is way too high and this is where I was hoping midplane stresses would be helping me out.

Anymore help would be appreciated.



Today is gone. Today was fun.
Tomorrow is another one.
Every day, from here to there,
funny things are everywhere. ~'Dr.' Theodor Geisel

 

[rb1957]

frank i'm confused ...

i read your earlier post as saying your rivets were 2024 ... and the later one as though they're 302SS ?

For 5083H32 sheet i'd use Fsu = 25 ksi (this is the O-condition strength) and maybe the perimeter of the rivet head (and the sheet thickness) to calculate the sheet allowable. if it is a SS rivet, then the sheet is much more likely to be the critical element.

 

[RPstress]

I think we could do with a sketch...

 

[GBor]

rb, I think the wire that is being held on by the rivet is 302 stainless...

 

[rb1957]

yeah, it'd help if i could read !

it sounds as tho the load is introduced onto the rivet head by the wire ... if the wire is looped around the tail of the rivet (before it is upset) i think there are enough squirrelly things happening there that the best way to develop an allowable is to try it (ie test) ...

as you pull on the wire the loading applied is going to be combined shear/tension, no? and probably bending too. how well will the "loop" hold ??

part of me wants to ask ... is it really necessary to subject a rivet to this sort of punishment ?

 

[GrimesFrank]

part of me wants to ask ... is it really necessary to subject a rivet to this sort of punishment ?

Ahh the $64,000 Question.
In reality this rivet is not subjected to this punishment, however my superiors think it prudent to determine what would happen if a sequence of unlikely events were to occur and the rivet is then subjected to these conditions.

The load on the rivet is introduced by snagging the wire on an object retracting perpendicular to the sheet face and pulling. As I have said the rivet pins the wire (through its solid loop end) to the sheet.

There are many unknowns this is a financal risk analysis for operation. I think I've proven sufficiently that the worse case scenario is that we've scrubbed one rivet and one wire.

I was hoping those of you in the aircraft industry had experimental data already on hand since you deal with rivets and Al sheets so readily.

Today is gone. Today was fun.
Tomorrow is another one.
Every day, from here to there,
funny things are everywhere. ~'Dr.' Theodor Geisel