Material substitution multiplication factor determination

[Mash04]

Hello,

Many materials or material product forms used to manufacture or maintain the original parts on today's vintage aircraft are no longer available or practical for reproduction to the original design data. To manufacture the needed parts requires materials or material product forms substitutions, such as substituting aircraft metals rarely used today with an equal to or improved material.I came across a technical manual (TM 1-1500-204-23-10)that had multiplication factors for various metals. Would anyone know who how they came up with the multiplication factors?

Link

See snippet from the TM and SRM in the attachment

 

[Sparweb]

Probably nothing more complicated than:

FTU (2) / FTU (1)

If they don't give references for their claim then we can only guess. I would rather not attempt to reproduce the table just for the sake of confirming where it came from.

Most sheet-metal structures have a buckling failure mode. That won't be affected Ftu as much as by Young's Modulus.

Many tempered aluminum alloys have roughly the same ratio of Ftu / Fsu (tensile strength / shear strength). It's usually about 60%. That ratio is not the same when comparing different tempers.

http://www.sparweb.ca

 

[Mash04]

Thanks SparWeb, i got that ah ha moment!

 

[WKTaylor]

There is an FAA AC for Vintage acft Parts and materials substitutions. WX is snowing-freezing where I live, so unable to access work PC for the exact AC number.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
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", Homebuiltairplanes.com forum]

 

[rb1957]

Seems very simplistic … what about fatigue ? (was 2024, is 7075 ?) what about corrosion ? was clad, is unclad ? was 7075, is 2024T3 ??

another day in paradise, or is paradise one day closer ?

 

[LiftDivergence]

I believe that is AC 23-27?

The excerpt from TM 1-1500-204-23-10 appears to be an exact reproduction of the material substitution table from a certain major OEM, notes, example, and all.

rb1957, I agree it seems simplistic. I realize the gauges are all being increased, and this table only applies to sheet structure. But it says it can be used for formed parts. If the factors really are only based on Ftu, I'd be concerned about substituting material for structure in compression. Again, the gauge is bigger, but maybe the factors should be greater if the same stability needs to be maintained.

Also, damage tolerance and cyclic load characteristics is a good point. Maybe that is one reason for Note A - basically 7075-T6 can't be used for pressurized structure? But again that seems too simplistic. Wing structure might not be pressurized for example, but it is still subject to a spectrum and has a GAGDR, albeit different from fuselage structure.

Keep em' Flying
//Fight Corrosion!

 

[Sparweb]

Attempting to find a copy of more of your document...

https://www.chinook-helicopter.com/...nce_Technical_Manuals/TM_1-1500-204-23-10.pdf

I think I know the source of this document - it is probably not worth it to pay EverySpec any money for it.
It seems to be a military equivalent of a document known in civilian sphere as "the Strutural Repair Manual".
But a modern SRM has repair data that has been specifically tailored to a particular aircraft. This one is just generic.
There are some nice cut-away drawings of helicopters and fixed-wing a/c's starting on page 40!
Something like this was circulated by my college instructors as "public domain" data for us to practice repair designs.

http://www.sparweb.ca

 

[Mash04]

Further substantiation will be required definitely! Functional area were the part is to be used plays a role and that has to be factored in. @ SparWeb i thought EverySpec provided free supply of military specs and some other specs.

It is simplistic, but why would OEMs have such data in their SRM? Wouldn't the substantiation of such data gone through scrutiny of the approval body prior to being entered into an ICA or continued airworthiness document?

 

[WKTaylor]

The following FAA documents may be useful...

ANM-112N-06-04 FORMER ALLOY AND TEMPER DESIGNATIONS, ALUMINUM AND MAGNESIUM ALLOYS

LD... You were correct...
FAA AC23-27 Parts and Materials Substitutions for Vintage Aircraft

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true. [Unknown]
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", Homebuiltairplanes.com forum]

 

[Sparweb]

Everyspec.com has gotten better over the years. It hasn't been this comprehensive for long. My habits change slowly. Truth be told it didn't occur to me that the whole thing might be downloadable there. Stuff like this is often behind a pay-wall, even when it's free from the authoring agency: the US Military. I still prefer to use [link quicksearch.dla.mil]ASSIST[/url].

http://www.sparweb.ca