Tensile Allowable for NAS1398B Blind Rivet

[ajlstress]

I am currently seeking advice on acceptable tensile allowables for NAS1398B Blind Rivets, it appears that the established references like Bruhn and Nui do not supply any clues for reference data.

The 10% of shear allowable as determined by MMPDS would be too conservative in my application and I do not really want to be forced to change the design to a bolt!

My application requires a 5/32 inch diameter protruding head blind rivet in 0.063 thick 2014T6 backing material.

Any advice would be really appreciated.

 

[CRACKKILZ]

An NAS1398B blind rivet crosses to a CR2263 cherry lock (Ref DC-9 SRM 51-30-0 Fig # 92). Per the Cherry/Textron Tech data sheet, a 5/32" CR2263 has an ultimate tensile strength of 375 lbs. They reference MIL-STD-1312 and NAS1400 as the source of their data.

I have a couple of comments also:

1. The data above is for the fastener only. Sheet pull through failure mode should also be investigated.

2. As a general rule blind rivets and indeed solid rivets should not be used where the primary loading is tensile uless the magnitude of the load is very small.

Hope this helps.

 

[SuperStress]

I have a proprietary company manual that supports CRACKKILZ numbers.

(They actually show 372 lb. for 2024-T3C and stonger).

This manual references the Rebublic Structures Manual and NAS1400.

SuperStress

 

[ajlstress]

Thanks for your response CRACKKILZ & SuperStress.

I am keen to find a reference that shows the effect of joint thickness on ultimate tensile strength for the NAS1398B or any blind rivet would be very helpful.

Thanks.

Ajlstress

 

[CRACKKILZ]

The only data that I can find is for "solid rivet tension allowables in various thicknesses of 24ST alclad sheet". The data comes from the design offices of the Glenn L. Martin Company .... Detail Aircraft Structural Analysis Supplement Pamphlet # 8.

According to this reference: For a 5/32" diameter universal head solid rivet in 0.064" 24ST alclad sheet, the rivet tension allowable is 640 Lbs.

Therefore it looks like your blind fastener will be tension critical at 325 Lbs.

 

[CRACKKILZ]

Sorry, I meant 375 lbs.

 

[ajlstress]

Crackkilz, thanks for your further response.

It appears that tension capabilites for blind rivets are not quoted in ANY Design Handbooks and as the failure mode of the blind rivet is not generally a head or tail failure but due to tail pull-out from the backing material I do not feel I can base my calculations on the Cherry datasheets using quoted values from a steel sheet backing material.

So it looks to me that unless you perform a full set of qualifications tests on the blind rivet in question in the design intent backing material you are forced to select a solid rivet and use a reference like Nui or Brauhn to qualify your calculations.

Thanks again for your research on my query.

Regards

ajlstress

 

[rb1957]

isn't there room for judgement ?

personally i'd be nervous of the tension capability of a blind rivet but if it was a reasonably small load and not fatgiue or vibration then maybe.

you say "full set of qualification tests". this is a daunting task, maybe a limited test say 10 specimens would give you enough confidence. the advantage is you can set the specimen to exactly your design, and see how the rivet is failing, and so be in a much better postion to argue your case.

on the other hand, you seem to be willing (reluctantly) to accept a solid rivet, so this choice isn't too difficult to accomplish, and a much better design choice.

 

[ajlstress]

Thanks for your thoughts rb1957.

I was just hoping that some published data was available that I could refer to in my calculations that showed the effect of backing material thickness - life is never simple!!

I totally agree that a solid rivet or a bolt would be a better choice and easy to justify but I have been given the task to justify an existing design using the blind rivets and I do not have the budget or time available to conduct the tests.

So I guess I must conclude that the design is not acceptable without test results confirming that the blind rivet performs above the required tensile load unless any other of our learned engineers can recommend another solution to my problem.

 

[rb1957]

"an existing design" ... is this something approved, or just something somebody drew up ? is it in-service ?

if it's approved and/or in-service either it's good or it isn't, and if it isn't then you'll need to revise the in-service applications (service bulletins)

 

[WKTaylor]

ajlstress...

Ref NAS1400 [NAS1398 & NAS1399 procurement spec], Table IV "tensile strength values", quotes the minimum required tensile strength for NAS1398B5 as 375#.

CAUTION: this is fastener tension allowable for parts tested in thick members. Thin or low-yield sheet pull-thru is still possible. CAUTION: the required tail on this type rivet is very small and I've see them pull thru in sloppy [loose-hole-fit] installations [be very careful to install "by-the-book"]. I would [personally] dictate a design MS [tension only] of MS=0.5 (0.66 factor =250#) for normal installs; or MS=1.0 (0.5 factor =187#) for critical installs.

HINT, GUYS: when all else fails, take a peek at the base and procurement specs for MS NAS & AS fasteners... there HAVE TO BE minimum requirements for the fastener type/size/alloy... otherwise there is no way for fastener OEMs to qualify the fastener. MIL-HSBK-5 [MMPDS] provide best resource... specs are only second best and may/may not be accepted by "authorities". NOTE: SOME fastener OEMs have MIL-HDBK-5 quality/format data available... but not formally published due to the expen$e/trouble... or it was "developed" for another customers.... who allows it to be released.

Regards, Wil Taylor

 

[ajlstress]

Thank you for your valued response Wil.

I have requested data from Textron Aerospace Division in Santa Ana and all they have supplied to date is copies of MIL-HDB-5 for shear allowable when I specifically requested data for tension in thin alloy plates!!

I believe your recommended minimum allowable in critical locations of 188lbs seems to provide a good margin of safety and I will see if this can be accepted.

Thanks again for your advice.