NAS1321 tension

[pudgala]

Anyone know where I can find tensile strengths of NAS1321 slugs in various panel thicknesses? This is not a primary loading condition but a seconday loading design requirement from wrinkling.

 

[MNLiaison]

The only public rivet joint tension allowables that I know about are located in the NASA Astronautics Structures Manual (TM-X-73305) in section B1 page 8. This is not specific to any single type of rivet but is general for universal heads and all flush heads with varying diameter. The sheet material is 2024-T3 and 2024-T36. You could use this data if you feel this represents your joint configuration and is deemed to be conservative. The NASA document can be found on either the NACA report server or the NASA report server and is free.

Just as an additional unrelated note, the Manual is the only reference out there that I have seen that has stress concentrations factors for figure eight holes.


Regards,
MnLiaison

 

[pudgala]

Thanks. I have this manual and have just looked it up.

There is a wide variation in what should be used for allowable slug rivet tension. For 1/4" csk, NASA quotes up to 2265 lbf. I have some in-house test results that are up to 2648 lbf.

However, we have a design value for tension that is 10% of the allowable shear load. I am told that the shear allowable is up to 1473 lbf. This corresponds to the lowest NASA value with fsu = 28 ksi. So my design value is merely 147 lbf.

My design requirement (wrinkling) is 806 lbf, so I have a wide range of possible RFs between 0.18 and 3.29! I have a suspected rivet tension failure on test, which suggests that the actual strength is no more than 806 lbf. It would be very welsome to find some allowable tension loads to corroberate this.

 

[MNLiaison]

From my understanding of your last post you have actually performed a physical test and you observed fastener failure.

Curious question. Did the fastener head pull through the sheet material or was there a different failure mode?

If the failure mode was not the head pulling through the sheet material shouldn't you have to look at an interaction curve for combined fastener load in both tension and shear in lieu of comparing each of them seperately. NASA reference publication 1228, Fastener Design Manual, has interaction curves for this combined loading. This may provide insight into why your fastener failed.

Regards,
MNLiaison

 

[pudgala]

In the test I refer to, which was a large fabricated panel with several stiffeners under compression, whole joints unzipped. There was an equal mix of pull-through and shank failure. It was not really possible to identify precisely where it began - i.e. whether the initial failure was pull-through or shank tension. Some realistic measured allowables, with their failure modes, is really what I am looking for. It seems that the failure was premature with respect to, for example, the NASA manual values.