FTI did a bunch of testing years ago with these in composites. Seemed to work ok. I don’t know of anyone who has actually used them (probably due to cost).
Rb1957, I think they are good for composites because they are advertising them as such. I think they are good for primary structural applications. Click bonds are not for primary structures.
I just heard from a former colleague ( I was searching form different sources) they used these for structural access panels, due to the close tolerance of the holes, they bridge the load path between the access panel and the surrounding structure where the panel is installed.
ok, I had a scan of your attmt but didn't see a mention of "composites". I'd've thought that cold working was not good for composite resins. I can see that they'd work with metal, due to the cold working. I'd be hesitant in saying that a/nuts are good for primary structure (and similarly that clickbonds are not good for primary structure). Conventional a/nuts are what you use for access covers and the like. If you're concerned about the satellite rivets, then install on a clip (nut plate). The problem I have with clickbonds is when the bond fails with the joint disassembled.
"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.
my 2cents ..
Been thru the Click-bond episode bunch of years ago / replacing damaged nut-plates at a pressure bulkhead. (don't ask)
seemed like an ideal situation that could avoid stress concentrations by eliminating the 3/32 nut plate holes .. even had the click-bond sales guy show up ..
- only problem was that no inventory was currently available .. Now /would we be interested in purchasing 3000-5000 units? ..
- also the bonding is only as good as the existing primer; easy issue with newly fabricated parts; but with repair/rework - what is the condition of the existing primer .. is there contamination of the surface? is the primer chipping off? adhesion to fresh primer differs to primer that has been exposed to heat and solvents. Just imagine how popular an engineer could be should the nut plate dis-bond allowing the nut plate to spin - not allowing the access panel to be removed & delaying a flight!
Also with the force-mate version nut plates .. review dissimilar material corrosion / is the location susceptible to moisture? - like cargo flooring .. or cabin condensation ..
suspect a steel insert installed internally into an AL alloy extrusion would be an expedient short term fix and extremely painful long term nightmare .. due to excessive exfoliation corrosion.
- also note the incidental costs .. tooling / personnel trained in installation / stock / & the ever present documentation - techs running around for an hours attempting to get the approval to install a substitute part..`.. again - spinning insert is not an easy item to replace without causing additional damage.
Because they are cold-worked [CX'ed] in-place the holes are 'larger'... IE: parts have to be suitable for these larger holes and the forces of installation... and the FTI CX tools [drills/start-reamer/finish reamer/CX puller/mandrel/sleeves and the Force-Tech bases and the nut-plate replaceable elements have to be coordinated.... and of course training is involved.
Once installed, removing/replacing a defective/damage nut-element is a 'piece-of-cake' for the field. Weirdly... In the case I was vaguely referring to [above], the maintenance shop, after mod'ing ~40-jets, arbitrarily decided NOT to install these parts anymore and use conventional nutplates [riveted-on like the old/established practice, due to the intense training and labor and parts and tooling involved. Drove us crazy when this happened. See ** for more of the story.
In composites, FTI ForceMate bushes [I think] have a special CX-in-place sleeve-bush to reinforce holes in composite structure... such as holes for lugs and high-use panels/doors with peripheral fasteners... or so advertised. The soft sleeve/bush OD actually 'embeds into the fiber-ends surrounding the hole when the bush OD expands into the hole'... quote-unquote.
I began working with FTI in ~1986 for T-37 wing-lug hole CX. Let me re-emphasize... formal training and re-current training and following prescribed practices is essential... and benefits can be huge.
CAUTION.
I once asked the USAF GURU on fatigue, Dr Lincoln, 'why the dramatic fatigue benefits of CX of aluminum aircraft structure could not be used/counted-upon in the DADTA analysis'... instead the analysis proceeded as if these holes had NOT been CX'ed'... the ONLY benefit allowed was simply as 'fresh-reamed/NDI-OK' hole for DADTA [re-set life of the hole, larger diameter]. His answer was startling, but wise: CX of all kinds has rich/powerful benefits... TRUE... but a single process error among thousands of holes will leave that [ONE] hole vulnerable to conventional fatigue crack initiation/growth. That, BTW, is why it was recommended for an independent inspector to look into each CX'ed hole and mark-it-OK... before shop is allowed to finish-ream to-fastener-size... in order to validate that the hole-bores had the CX sleeve 'end-gap-line' evident... confirming that hole expansion had occurred. NO LINE = hole was 'missed' or the 'process failed', somehow.
** War story. FTI Nutplates were mod'ed to an aircraft we were working on as a 'formal request'. About 40-aircraft of 400 were modified with these ForceTec Nutplates... in-lieu-of the conventionally riveted nutplates. Great! We all went thumbs up and walked away. Little did we know that the shop managers and mechanics got together and quietly decided that the process... training, tooling, disposable parts, FTI Nutplate assemblies, time/labor, etc... was not cost effective to accomplish on the allotted budget. YEP, they quietly went back to the 'old standby riveted-on nutplates' without telling higher management and any engineers... and diverted the assigned budget to 'other tasks'. We went insane when the field called for spare/replacement nut-elements... and found out no-one knew exactly where the FTI parts in the unused Mod-kits 'went'... and 'by-the-way, weren't using them anyway'. After scrambling-around, the Kit-parts were found 'accumulating' in the back of a store-room. Deja Vu to Dr Lincoln's very wise 'real-world-perception' of events and people and awsh*ts. OH YEAH, and top leadership gave 'forgiveness' to the shop.
Engineering is easy... people are hard.
Regards, Wil Taylor
o Trust - But Verify!
o For those who believe, no proof is required; for those who cannot believe, no proof is possible. [variation, Stuart Chase]
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion", HBA forum]
o Only fools and charlatans know everything and understand everything." -Anton Chekhov
yeah, I get Jack (and Tom) etc but ... one single imperfect hole shouldn't (IMHO) invalidate the thousands of good holes. There's a tonne of testing and validation. The effects used in the analysis are like B-basis. Follow Jack's opinion, and every plane should be fatigue tested to failure (before delivery !). Mind you, the biggest issue with USAF damage tolerance is "slow crack growth, non-inspectable" ... if the flaw crack growth is more than 2 (or more ?) airplane lifetimes, then never inspect.
As for improper part substitution ... well, that's it's own problem. Sure, during a "firing" war no one is going to keep a plane U/S for an a/nut, and no one is going to document it. But after the war is the time to inspect, find these errant substitutions, and fix them.
"Hoffen wir mal, dass alles gut geht !"
General Paulus, Nov 1942, outside Stalingrad after the launch of Operation Uranus.
