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Gusset stress damage

J

jwilbur

Well Known Member
I'm working on the mid fuse bottom skins and while maneuvering around the shop I managed to put enough pressure on one arm of the fuselage bulkhead (page 25-8) to change the angle of the gusset holding the two pieces together. I gently bent it back to the proper angle and noticed what looks to me (an untrained eye) like the gusset is now forming a stress crack. It's not cracked yet but the aluminum is discolored and I don't like it.

Do I just put a doubler plate over this or should I reorder the gusset and replace it? Note that it's in a tight spot to drill and re-rivet so any additional advice is welcome.

Close up what I believe to be the start of a stress crack.
2013-09-02_12-18-28_353.jpg


For context:
2013-09-02_12-18-38_575-1024x768.jpg


Thanks,
 
Probably a non issue, IMHO, due to the side skin immobilizing the area, and partially carrying the load when it gets installed, but I would check with Vans, this is what their support folks are there for.
 
Mike S said:
Probably a non issue, IMHO, due to the side skin immobilizing the area, and partially carrying the load when it gets installed, but I would check with Vans, this is what their support folks are there for.
Click to expand...

Thanks Mike. I sent a message to Van's.
 
I wish I knew how to get a better picture. The pics look like a scratch. In real-life it's a discoloration (like plastic before it breaks), not a scratch, and it just "feels" weaker than the other side. I'll see what Van's says and maybe have a tech-counselor look at it. I want Mike's answer to be right (build on) but I'm just going to make doubly sure on this one. It just doesn't feel normal to me.
 
The unintentional bend is definitely "with the grain" which is not good. This can cause cracks. Not quite sure why that part has the grain running crosswise.
Of course I can't see the complete part. Maybe there is something I don't see that would explain it.
 
Aluminum alloy is an extremely complex structure, often comprising between six to nine different metal elements. In a molten state, during alloy production, some elements are dissolved in others (like cream in coffee) and some are not (like oil in water). As the molten alloy begins to cool a point will be reached when solidification begins. At that point ?crystals? begin to form and, as cooling continues, more crystals develop, building on the first to form a metallic grain structure. Other compounds may also form within the alloy as it cools, some dissolved within the grain structure and others between the grains, along grain boundaries. The malleability, ductility and strength of the alloy are all dependent on the nature of the final alloy grain structure. The grain can be seen by viewing off the shelf sheet and noting the direction of visible lines running end to end. Bends should be made perpendicular to the grain direction.
 
Best Explaination

Wayne,
That's probably the best layman's explaination of how how aluminum is made that I've ever read, thanks.
 
BonitaRV8 said:
Looks to me like a mark made whent he two parts touched when it was initially bent?
Click to expand...

This is what Sterling Langrell from Van's support thought also, but said he couldn't be 100% sure and it might be worth replacing if only for peace of mind. I think I'll leave it alone until I finish the bottom skins and re-examine after I get my mind on something else for a little while. Fresh perspective and all that.

Thanks everyone for your comments. And +1 on Wayne's explanation of Aluminum. That was very instructive.
 
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