Do not do this unless there is a legitimate reason there is no alternative.
Transitional joint strength not really semi-empirical, it is mostly derived from testing. Reduction in strength for microshaving is not easily calculated, and certainly not reliably. This is because the microshaving process is highly variable especially for 1-off situations like this. And usually SRM shaving allowables have test data to support them. Surprised a DER is ok with that tactic.
Either you point to an SRM procedure which allows microshaving for your particular scenario, or come up with something else that doesn't require it. And you're probably SOL with SRM since none that I'm familiar with allow blending at fastener locations, for good reason.
Do NOT install rivets "flipped" to shave bucked end. Shaving the bucked end is just as bad or worse IMO than shaving the head, especially after bucking into as csk.
If you are just talking about a blendout at a few fastener locations, it will literally make zero difference having a few protruding heads on the OML.
It's not worth the analysis headache. I strongly suggest:
1. Remove all fasteners c/t the blend which will require microshaving
2. Drill out to next rivet size up, providing nominal spacing range is maintained.
3. Manufacture csk repair washers at locations for remaining csk as req'd
4. Install protruding head rivet w/ csk repair washer on skin OML
Unless you have access to internal loads data, substantiation will need to be "creative". You can't compare to allowable damage limitations from the SRM because they won't allow blending at fasteners specifically because of the effects on joint strength. You say you're calculating a ~3 percent reduction in fastener allowable. But what does your method account for? The head is going to be less stiff and have less bearing area to support secondary bending moment, load transfer (R/P) is going do change throughout the whole joint stackup. What is the joint? A shear tie? A stringer? Not saying it's impossible to show good, but please don't over-simplify it. That's not even accounting for the effects on damage tolerance of the skin leaving an unreinforced blend at a joint location.
Just put in a bigger rivet and switch to protruding head with a csk repair washer... done.
For reference, there are several other threads discussing the issue of microshaving:
I am looking to get correct information on rivet shaving. I work for a Aerospace company in stockton ca. I know the process being used on winglets is incorrect. ME's and QE's dont want to deal with it.
It is my understanding the indents on the heads of a flush clinch rivets should still show and that the rivet shouldnt be shaved more than .010.
What is happening is the Techs are setting the rivets countersink low so the rivet will set high and then shave them flush leaving the dia. of the head now reduced, thus jeopardizing the integrity of the rivit as it was designed.
The parts...
Lately projects keep getting more difficult with a new twist each time.
I am required to install an antenna Reinforcement to a .032 Thick crown skin. Customer insists on having no external Doubler.
Since aircraft is CAR 23.573b regulated (DTA Analysis requirement)- the following options are available.
1/ Dimple NAS1097AD4 rivets in .032 skin & CSK into Doubler.
2/ Use greater quantity of NAS1097AD3 rivets
3/ elect to reduce CSK head depth of NAS1097AD4 rivets
4/ Metal to metal Bonding.
I would prefer (1) but require fatigue data for Dimpled fastener locations.
(2) would be the simplest to...
Recently, I have been asked of the maximum allowable of material to be removed from a fastener head for a countersink rivet to be considered structural. As an example, A NAS1097AD7 rivet in a 0.040 inch thick 2024-T3 materia, the maximum depth of countersink using Boeing guideline is 66% of material thickness, giving a max depth of 0.026 inch. Therefore, the countersink head might not have sufficient bearing area in the countersink hole and tensile properties. Are there industrial specs or test or maybe guidelines to follow on shaving rivet heads.
Another question I had is can a mechanic...
