Filling up unused holes in Steel and Ti structure 4

[stressiterior123]

Can someone provide me good reference for Filling up unused holes in Steel and Ti structure?
Can I use Al rivets to fill up holes in steel and ti structure?
Newbie here any help will be apprecitated.

Thanks

 

[rb1957]

i wouldn't ... i'd use steel for steel and Ti for Ti ... but now you'll say "it's a tooling hole going through both"

before i'd say use Ti for both I'd want to know the type of Steel.

how about leaving the hole open ?

a great/expensive/OTT "repair" would be to bush the two holes separately ... freeze fit, 0.001" - 0.002" interference, 0.032" min wall.

 

[stressiterior123]

AISI 301 is the steel
I cant leave them open Fatigue DT DER insists on having them filled.

 

[ESPcomposites]

I agree with rb and would suggest to use the same material for the plug.

As you mentioned, the issue with leaving it open would be DaDT issues. The whole point of filling it is to make sure the plug picks up load and reduces the stress concentration around the hole. If you put a softer plug in, it will be less effective (though I cannot quantify how much). Alum would be 1/3 the stiffness and quite a large mismatch. My gut feel is that the alum plug would still be quite effective, but would it match the effectiveness of the expectation? Probably not.

Brian

http://www.espcomposites.com

 

[rb1957]

so are they a common hole ?

if so i suspect you'll need to bush each layer separately ... though i guess you could use a Ti plug ... i guess the stell and Ti parts share a common face, without protection (eg fay sealant) ??

 

[WKTaylor]

stressiterior123...

Technically a plug should be a close match-to, or exceed, the stiffness, strength and HARDNESS of the base material. The plug supports the hole wall from deforming during elastic loading... which is the primary reason open holes develop cracks rapidly.

A less stiff/strong/HARD plug [aluminum in Ti or steel, ~10:16 or ~10:30 stiffness, strength and hardness ratios] will provide very little reaction reaction force [due to lower stiffness] on the hole wall. Not to mention that the lower-strength and softer material could actually be damaged by the harder material [scratched, cut, deformed, etc].

A stiffer plug [Ti or steel in aluminum] provides a stiff/strong/hard static pressure force on the hole wall, preventing any deformation or plug damage.

NOTE.
I have successfully used "net-fit" [Boeing guys: "transition fit"] TENSION RATED low interference-fit fastening systems [PH bolts + washers/nuts or HL Pins and collars] to plug holes in aluminum, Ti, CRES, steel and HRA structures. The idea is to fill the hole tightly... then using the tension pull-up from the head and nut/collar [nut/washer or collar torque-up] to place the fastener head/tail in high static tension, resulting in an additive compression force against the surface material SURROUNDING the hole. OH yeah... cold-working the hole and installing this fastener system really helps to bump-up fatigue durability at these holes [retards crack initiation at the hole wall/lips].

HINT: this "system" really works remarkably well for retarding crack initiation in stop-drilled holes at the ends of cracks.

See NAS618 [Fastener, Recommended Shank, Hole, And Head-To-Shank Fillet Radius Limits For] for "standard" hole-to-fastener net-fit and low-interference fit dimensions.

NOTE: I have used large diameter fasteners [straight or tapered shank] to plug holes in one [outer] layer of a stack-up that was cracked... then drill thru the middle of the remaining smaller Dia hole for installation of a smaller Dia [less stiff shear] fastener thru the total stack-up.

How? The hole is reamed for a tight fit with the humongous fastener; and the fastener shank is cut/milled off so the stub-end will be flush with the opp side of the same layer [IE: opp side of the spar flange or skin, etc]. After reassembly the center hole is then back-drilled thru the remaining original smaller hole [good hole in the mating structure] to establish the thru-hole for the replacement [smaller Dia thru] fastener. The retained fastener head helps prevent the "plug" from "migrating" like a straight-walled headless plug might.

[this makes sense to me... hope it still makes sense to everyone else].




Regards, Wil Taylor

 

[YoungTurk]

Great post on a deceivingly simple question Wil!!

Since the OP is a self-identified newbie, and nobody else has mentioned it, I'll add that you need to be cognizant of galvanic corrosion issues in mis-matched materials, especially those exposed to moisture either in service or at installation.

 

[WKTaylor]

YT... very good point...

There are definitely issues with dissimilar materials... although tightly adherent coatings and sealants/sealing [with corrosion inhibitors]... IE: multiple layers of isolation.... can provide fairly long-term corrosion resistance.



Regards, Wil Taylor

 

[Sparweb]

Have I missed it or do we know the size of the hole(s) in question?

My answer would depend on the size of the hole.

What does the SRM say? (If there is one applicable to the airframe or part)

Is the hole in a sheet-metal part, machined part, or forging? I'd go with a freeze-plug in a thick plate, but if it's 0.016 sheet, then that would be pointless.

Steven Fahey, CET