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?

 

[Sparweb]

how would the "NACA flush" type rivets compare from a fatigue perspective??

Ooh, I doubt that the NACA took on that question, but it's a good one. I have no idea where one would find test data.
Better yet: never do this in a fatigue-sensitive joint.

I'm pretty sure there is a NACA WAR report for shear allowables for NACA method flush rivets.

I want to go looking for that. Would NACA have gone to the full extent of coupon tests needed to satisfy the A-basis (95%/95% ) value?

 

[WKTaylor]

There are several NACA documents on riveting allowables, various methods/types, from the 1940s... not nearly as sophisticated as M-H-5 or MMPDS... A, B statistical allowables. I don't have the time right now to paw-around in my data files**..

/CAUTION/ Some stress weenies get pretty tense/rigid when dealing with old data in unfamiliar or scanty presentations.

Also, my company has proprietary data on fastening allowables. I have many... but wary of posting**... from my corporate library. You may find similar in NACA data libraries... or corporate or college libraries.

IF you're able to find a copy, there is a document with the dramatic title... "Making Fuselage Rivetted Lap Splices with 200-Year Crack Free Fatigue Lives" that emphasizes the amazing fatigue-life improvements in lap-shear joints integrating NACA riveting methods... and 'why' the benefits for fatigue-life improvements [crack initiation-retardation] are real. Also... even if this report is not available to you [proprietary?], there are many current/related documents on riveting/fatigue life that reference this document... which could be useful.