crack growth data 1

[groveri]

I'm looking for an on-line source of crack growth data (da/dn), particularuly 6061 aluminum. Does anyone have any links?

 

[rb1957]

from AR-MMPDS-01, (from the FAA website) see fig 3.6.2.2.8

 

[groveri]

Thanks, that's a start, but I need the fatigue crack growth rate data - (da/dN) vs dK for 6061, like figure 3.7.6.1.9 from AR-MMPDS-01 for 7075.

 

[rb1957]

sorry about that !

can i ask why you're using such a relatively non-structural Al in a primary structure ? ... part of the reason you can't find data is that because people generally don't use it, so not much investigation has been done.

i've had a quick browse through some of the data at my desk, and couldn't see anything on 6061.

 

[groveri]

Actually, my customer selected 6061-T6, not me. However, the application is the liner of a filament wound pressure vessel and this is a common material for this application. I need the crack growth rate to predict the cycle life of the liner before leakage occurs for a minimum acceptable flaw size. The liner itself is thin relative to the carbon composite and is basically nonstructural and simply functions as a bladder and a "fly away" tool. The liner is autofrettaged by yielding during an initial sizing pressure cycle, so a ductile, high elongation metal is required. For this purpose there are even better alloys available. However, the polar boss is integral with the liner and some decent strength is required to prevent spitting out the boss (the ultimate pressure requirement is over 15000 psi). Alloy 6061-T6 seems to be a good compromise between these two requirements. Anyway, I did find some data for R=0 in the Air Force Damage Tolerant Design Manual. This will probably work, but I'd really like to have data at other R values.

Thanks for your attention to my question. Any additional information would be greatly appreciated.

 

[Nigel]

Sounds more like a fracture mechanics problem. Fatigue is only part of the problem. I will check what info there is on NASGRO and get back to you.

Nigel Waterhouse B Eng (Hon's)
Can-Am Aerospace,LLC, Canadian Aircraft Certification Centre

http://www.canamaero.com

 

[rb1957]

g'day groveri,

i think it's reasonable conservative to use R=0 data for stress cycles with R>0. i would be more concerned about the impact of your manufacturing process, it sounds like you're doing a lot of plastic deformation which might upset the crack growth.

actually that leads to a couple of questions about the stress cycle ... if its plastically deformed in manufacture, how does this interact with the applied loading (a bit like a cold worked hole) ... but then that may be why you want high R data ('cause of the mean stress from manufacture);
and, if the liner isn't particularly structural how (or why) is it taking load (maybe in proportion to stiffness ?)

if i understand, you're applied 15ksi as a service load (linear elastic) ... over the top of your residual manufacturing stresses, or does the boss have no appreciatable stresses ? if the boss cracks does everything get really bad really fast ?

good luck

 

[unclesyd]

You might want to check this site out. I’ve seen it referenced several times.

http://www.nasgro.swri.org/

You might check out this site form metengr. They have some data.

http://www.fatiguecalculator.com/constamp/index.htm

 

[rb1957]

NASGRO 3 has 6061T6 in its database ... i'll try to extract the info ... or someone else could too ...

 

[FranAle]

Groveri:

Also try AFGROW, USAF reference data for fracture and fatigue analysis. Email me if you need this package.
Good luck.

Fran Ale