Can I attach a 2024 T3 doubler to 2024 T42 skin?

[cadddict]

Greetings All

Is it good practice to attach a 2024 T3 doubler to 2024 T42 skin?
Should I be using 2024 T42 for the doubler as well?

Are there any major errors of using the dissimilar sheets?

Thanks in advance

 

[berkshire]

You are using the same material, you just have a softer temper.
So you would have to make sure you have accounted for the lower strength.

http://www.engineersedge.com/aluminum_tempers.htm

B.E.

 

[rb1957]

would consider these dissimilar ... as BE posts, there's a small strength issue to think about.

Quando Omni Flunkus Moritati

 

[YoungTurk]

Given that T3 is typical sheet stock, this isn't at all uncommon. T3 is cold worked, T42 is more commonly used for parts which are heat treated after fabrication - permitting easier forming but preventing the use of cold working.

One thing to check is whether or not both skin and doubler are clad.

Assuming you are using clad sheet in the .01 to .062 range, compare the MMPDS values:

Material - (Ftu, Fty, E)
2024-T3 - (60 ksi, 44 ksi, 10.5 Msi)
2024-T42 - (57 ksi, 34 ksi, 10.7 Msi)

 

[WKTaylor]

cadddict...

I has been my experience that 2024-T42 is only specified where forming -T3 sheet for skins is not feasible. I'll bet a paycheck that these skins were specified as 2024-O HT to -T42 on the PL [or -T4 depending on how old the drawing is]. The implied fab process is solution HT, quench, form in the W temper and then age HT to -T42... which ususlly resulted in extremely high fidelity contour matches.

For a -T3 doubler to work on a compound-formed -T42 skin, the contour at the doubler location [on the skin] MUST be essentially flat, or an easily formed single curvature [rolled or draped]. Otherwise there will be a doubler-skin contor miss-match that could be significant; and the -T3 doubler will have to be formed to contour by hammering, stretching, peening, "english-wheel" forming, cross-rolling, etc.

I am working a skin issue where the compound curvature is slight but definitely significant for the area in question. The material was defined originally as Clad 2024-O sheet HT -T42 [as described above]. Formed internal doublers and triplers were added later-on in production. A new generation skin was specified as thicker clad 2024-T3 sheet, special quality, to eliminate the doublers and tripplers. The material is supposed-to-be strech-formed in the -T3 temper, stress relieved, then chem-milled to effectively mimick the added doublers/tripplers and original skins thickness. The new skins have a almost flat-rolled appearance and obviously do not fit the area in question. Nothing is working-out for these new skins which will probably have to be trashed. I have my suspicions as to what went wrong... but am not at liberty to explain.

Regards, Wil Taylor

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