Shaved CSK NAS1097 rivet strength allowables

[SteveAero]

Hi,

I know that this subject has been broached in previous posts, but I am looking for something more specific.

Due to corrosion in the skin of a Boeing a/c, a blend out (from 0.071" to 0.068") was performed at joint locations. This means that the skin and NAS1097K fastener heads were shaved down by 0.003". The DER is requesting a calculation showing the reduction in the static joint allowable due to the head of the rivet being shaved down. I know of 2 sources that have such a calc-both HSB references from my time working for Airbus:

1. HSB 21020 calculates the head and shank Ultimate static allowables,
2. HSB 21025 provides a method to determine fastener joint strength allowable in case a fastener head becomes un-flushed after a rework (blend out) without adjustment of the countersink.

Both of these sources yield around 3% reduction in static joint strength in this situation.

My question: are there any similar methods in the public domain (or of American origin) that would yield the static joint reduction for shaved head NAS1097 rivets?

 

[rb1957]

AFAIK you are not allowed to shave 1097 heads. ... IDU, you mention something like 0.07" corrosion damage, but this leads to 0.003" shaving on the heads ?

I'd replace the rivets, and see if anyone can notice the 0.003" heads ? But if your DER will buy what you're selling then go for it ! IF you're saying that you know the Airbus methods, but can't quote them in a report, then, yeah, you probably need some test data to validate this for yourself. "HSB" is an airbus strength manual ?

Will will have more to say on this, I'm sure ... not that I'm poking at Will ... really ...

 

[WKTaylor]

Comment... NAS1097 what Dia/alloy??? #4, #5, #6... AD, D, KE...etc??

I concur with RB...

#1... Remove rivet(s) with shaved-down heads and 'shoot' new NAS1097xx's wet with primer... and allow the heads to 'ride' slightly above flush.

#2... Remove rivet(s) with shaved-down heads and install 1-OS [1/64] titanium shear-head Hi-Lok Pins [+ aluminum shear-collars] in transition fit, with sealant and allowing head(s) to 'ride slightly' high [with sealant squeeze-out to fillet around the edge of the head].... in AREA of skin rework.

#3... I have other 'aces-up-my-short-sleeve'... sorta simple to understand... but explaining them can be difficult to document.

 

[rb1957]

when we need a custom CSK (and are "happy" that it is not a critical installation) we'll sometimes shoot BB rivets, so they overfill the CSK, and shave flush.

or flip the rivet around, head on the inside, buck into the CSK, overfill, and shave flush.

 

[WKTaylor]

rb...

BB rivets are just a weee bit stronger than A rivets aren't they?

OK, reverse bucking with protruding head on inside, bucked-tail into 'what's-left-of-the-countersink' and above flush... shave the tail 'flat' +0.010-to-+0.025 above flush.