AA7079-T6xxx [sheet, plate, extrusion/bar, forgings, etc]: need for DADTA values, SN-charts, etc 5

[WKTaylor]

All... HELP!!!

Generally speaking aluminum alloy 7079-T6xxx, any form [plate/sheet, forging, extrusion/bar, etc], is ruthlessly efficient in destroying itself in the real-world, long before 'natural initiation of fatigue cracking', IE: SCC and/or EXCO will initiate damage/failures long before fatigue cracking becomes a problem... so that the typical crack initiation/slow-growth/fast-rowth/catastrophic failure will rarely ever have a chance to happen.

However, a fair question was raised recently: where do DADTA experts 'go' for authoritative data on 7079-T6 fatigue damage values, IE: dA/dN, KIc, KIscc, etc.This is driving me crazy: The alloy was removed from service years ago, and not too much DADTA testing or service experience was developed to garner statistically significant data... or so it seems! I presume that most of the remaining parts in-service, actually surviving are in dry or fuel-wet areas only.

I have been asked to track down this data for out DADTA weenies on a sister acft system. To a limited degree I have bits-n-pieces of data... but nothing strung together and authoritative. I'm asking All Eng-Tips members if anyone has a ‘clue-card’ where this data might exist in-one-place. I am aware of some info in MIL-HDBK-5 [early versions]; and other MIL-HDBKs to a lesser degree…. But that’s it. Had hoped that the ASMH might have some data… but apparently NOT. Even my ASM reference... Fatigue Data Book: Light Structural Alloys only has (1/2) page. I have been querying 7079-T6 and found a few other obscure references. Within my company, 7079 appears to have been treated with similar low interest, probably because it was forcibly removed from most commercial/military acft/service decades ago.


Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]

 

[724napier]

Link

Try the link above, if it doesn't work google NASA CR-996. You should get an older NASA document with a lot of information on 7079.

 

[blakmax]

Some data was in MIL HDBK 5 revision C, and if you can find a source for that the data may be there. As a hint, try someone who worked on F-111 because that aircraft had buckets of 7079-T6 in it.

Regards

Blakmax

 

[tbuelna]

I took a quick look at the document linked by 724napier. It's a very impressive 97 page report of extensive testing done in 1968 by Boeing on the fatigue/fracture characteristics of 7079 aluminum. I can't imagine the cost to perform this work back in 1968, but the title page states you could have purchased a copy of the report for just $3.00 US!

 

[verymadmac]

ASM's "Fracture Resistance of Aluminum Alloys: Notch Toughness, Tear resistance and fracture toughness" gives KIc for several sheet/ plate configurations of a 7079-T651, 7079-T6.

 

[tbuelna]

Did a search for "7079-T6" on the DTIC website and saw quite a few documents related to fatigue and stress corrosion of the material. Definitely worth a look.

 

[FastMouse]

I don't know if authoritative 7079 DADT data exists anywhere all in one place, but here are some more sources for bits-n-pieces of data:

ESDU 81031 Fig 16
da/dn for:
7079-T6 Plate, R = 0.2
7079-T651 Plate, R = 0.33
7079-T652 Forging, R = 0.33

I am unsure of the source of this ESDU data. The reference pages of the copy available to me have become illegible as time has passed.

HSB 63511-01 Fatigue Strength of metallic lugs due to constant amplitude axial loading
This data item includes what appears to be an empirical constant for use when extrapolating 7079 SN data (which the engineer has to provide) to R values not covered by the available SN data.

AFML-TR-65-170: Fracture toughness & fatigue of 7079-T651 (plus some other alloys). I have not checked this document to see if it is helpful, but it looks hopeful.

There is also some useful da/dn and fracture toughness data in the USAF DTDH.

 

[724napier]

I have a copy of MIL-HDBK-5 Rev C and it does have some data on 7079-T6. Let me know if you are interested and I can upload it.

 

[WKTaylor]

Thanks to all!

For the last couple of days 'have been 'digging-deep', starting with Your recommendations. Amazing how many of these documents have references pointing to other references [etc] that lead to many/varied authoritative studies... and in-some-cases very unusual, yet important parallel studies.

First, I noted that in the 1950s/early 1960s this alloy had lots of promise and the standard tests looked positive. Good strength, thick/deep section heat-treatment, low SCC,/EXCO [if properly protected], decent fracture toughness, etc. However actual service environment was never introduced to the 'dry air' fatigue studies. Real service experience has been a nightmare: the environment, thru SCC & EXCO interaction, accelerated crack initiation/growth, leading to multiple failure modes. I was also NOT surprised to find metallurgical issues emerging during wrought-processing; and several studies about effects of various heat-treatments.

One more-recent report seemed promising: retrogression and re-aging [RRA] dramatically affected metallurgical properties in a very positive direction; however, many emerging new generation alloys, with/WO this RRA processing, performed so much better in every way, there was no point in keeping 7079 active.

Thanks to all, my list of data resources for the stress/DADTA weenies expanded dramatically. The beauty of this is that multiple authoritative sources allow side-by-side comparison of each data set to refine the 'bigger picture' for all forms of 7079-T6 that might be installed on our older jets.

I must admit this has been a real education, my part.

NOTE. If anyone is interested in 7079, I could list of documents found/submitted… but I won’t hold my breath waiting for anyone to ask.
NOTE. 7075-T6, 7178-T6 and 2014-T6 were also found on many of these documents.
Hey I grew-up with these alloys, mid/late 1970-early 1980s… until discovering 7050, 7175, etc…
NOTE. After reviewing company documents, this other topics, I found several that revealed our guys in the Mid 1970s/early 1980s weren’t stupid and had a foresight of what maintenance/repair nightmares were-to-come on the first generation X

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]

 

[crackman]

Hi Wktaylor

Just as an added note to the wealth of information you have already found. Once upon a lifetime ago I used to be the USAF C5 ASIP manager. We contracted for a wealth of dadN data on the C5 as it contained 7079 all over it. You might try looking under the C5 and also I would bet you could probably FOIA a lot of data on 7079 from WPAFB.

Good luck

 

[WKTaylor]

Crackman... were You at SA-ALC [MMSRC] during this time?

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]

 

[crackman]

Hi Wil

Yep. Our DTA branch got renamed to MMEOD then laterLADD. Since our group supported C5 as wel as T37, T38, F5, OV10, they never new which division to keep us under.

 

[WKTaylor]

Crackman... Thought-so... Knew some of you DADTA guys...

I was in MMSRA ~1982--1988. Worked some low-level stuff on the F-5/T-38 and -106; and was gradually ratcheted up to lead structures for T-41 and O-2 then OV-10 then T-37 and A-37. Good training ground for my next (2) jobs [overseas].

I really miss Les Davis... best manager I ever had... saved my career and 'nudged' me away from that place [into 2 overseas jobs].

Are You still 'in the saddle'?

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]

 

[crackman]

Hi Wil

I left Kelly in 1991, worked for Jimmy Turner in the dta branch and I really enjoyed it. I agree, it was a good training ground and lots of great hands on experience. I left Kelly and went on to work at L3 and then several other OEMs. For the past 15 years have been in business for myself.

Regards

James

 

[WKTaylor]

Crackman... most excellent! Amazing where each of our diverging paths have taken us!

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]

 

[crackman]

Will
Good catching up with you. With regards to 7079, I will look and see what I have. Remember, C5 was lousy with it and we had tons of issues with 7079.

Take care

 

[WKTaylor]

Crackman... appreciate the help!

There is a back-channel for contact thru the Eng-Tips staff. If You find any significant 7079 data, please contact them to contact me, so I can dig gold out of Your back pocket.

This subject is infuriating: since industry/DoD made this alloy 'go-way', those of us still stuck-with-it on our acft have dwindling resources and support.

NOTE. Data on use of 7079-T6 in F-111 interesting... and disturbing. Weight was such a premium, GD took a big risk. No wonder all FB-111s have been retired... not to mention the UHS D6AC steel wing-carry-thru center-sections that had a nasty habit of sudden catastrophic failure from relatively tiny defects.

IF I recall correctly the F-14 began to have similar problems with it's titanium wing carry-thru center-section.

Hmmmm… how many of You [are old-enough to] remember the kiosks at airport terminals where You could get short-term life insurance for a few bucks, just before boarding a commercial flight? Haven’t seen those in Years!?? Anyway... One of the funniest, but not-so-funny, political cartoons I ever saw was of a “worried-looking naval aviator filling-out flight-insurance forms at the kiosk on-the-deck, just before taking-off in an aging/drooping F-14 sitting in the background”.

Regards, Wil Taylor

o Trust - But Verify!
o We believe to be true what we prefer to be true.
o For those who believe, no proof is required; for those who cannot believe, no proof is possible.
o Unfortunately, in science what You 'believe' is irrelevant. ["Orion"]
o Learn the rules like a pro, so you can break them like an artist. [Picasso]

 

[crackman]

Will

Not sure how to contact you thru eng-tips staff. Let me know how and I will see what I can do.

Thanks