Repairing Aluminum Gouge

[TLHS]

I just got a question about a severely gouged aluminum square tube member that's part of a telescoping boom. There's a reasonably big area that's been gouged out at the corner of the tube in one location. There's no measurements at the moment, but it looks significant enough to me that it'll compromise the rated strength.

Here's the problems:
-It telescopes, so you can't add to the outside or it won't sleeve into the larger member
-It's aluminum, so filling the area with weld metal and grinding flush isn't going to get me to base metal strength necessarily
-I can't figure out how I'd close the thing back up again with full moment strength if I cut it open to reinforce from the inside

I'm going to start digging through the aluminum welding codes soon, but I'm pretty sure I'd need to post weld heat treat this thing to get it back to original strength if I started welding to it? That seems problematic.

I don't see any way to reinforce this without adding material on the outside, and it seems like that's a no-go.

I've told them to start by going back to the manufacturer, but if this ends up back in my lap I'm having a conceptual think about it to see if I can even offer an option.

 

[Ron]

Yes, PWHT would be necessary. Probably a 60 or 70 series alloy, so finnicky at any heat affected area.

 

[dhengr]

TLHS:
You need a lot more info. on this gouge, size, depth, location on the boom member, photos, etc. etc. You will end up dealing with which is the worst of several evils, and picking/offering the least critical option as a possible solution. And, the gamble should not be yours, you are only giving the risk takers, the decision makers, your best engineering judgement of their alternatives.

Where is this gouge on the whole boom section as this relates to max. canti. boom moment, max. torsional and lateral moments, max. concentrated loadings and reaction? How does this look in terms of reducing the section properties, and in terms of its orientation as a stress raiser. If it is on and along (parallel to) the neutral axis w.r.t. the max. bending stresses (particularly tension), it may not be too serious. If it is across a tension flange and at a high stress point it is probably a deal breaker. And, all you can do is explain these alternatives, with some reasonable engineering assessment of the risk potential. But, the risk or decision should not be yours, nor should you be the insurer of last resort, unless you caused the gouge. You might be able to grind and fare-out the gouge to make it a much less severe stress raiser. Alternatively, a new boom section might be the best, most cost-effective solution, with a minimum of risk taking for all parties involved.

 

[TLHS]

dhenger,

Yeah, I'm definitely aware that I need a bunch more information. I'm just running this in the back of my mind at the moment based on what I know since there's a chance that someone comes back and asks if I can help.

I'm trying to figure out if I feel like I can offer a solution or not at this point, based on high level info. A go/no-go on the project. I think this might come down to whether the existing section with the gouge is acceptable for the loading. I don't think I really want to be the one taking that on, if it's the case. The fee doesn't match the risk or the complexity of the work. If I can figure out a way to reinforce, though, I'd likely be comfortable doing that.

 

[NorthCivil]

Why would something like this even cross the desk of an engineer?

They likely took it to a welder, who told them you cannot weld aluminium without massive loss of strength, they said I wont do it, "well what if we get an engineer to sign it off?"

replace the part, thats what a reasonable mechanic would do. maybe with steel this time in anticipation of the next time there is a gouge

 

[rb1957]

could you test the part ? either as part of the arm, or in isolation ? If the arm starts to deform at the gouge you're not much further behind.

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

 

[BridgeSmith]

It makes a tremendous amount of difference where the gouge is located:
Tension face - fairly straightforward reduction in strength; fatigue could be an issue if they want to continue to use it that way.
Compression face - Now you have to worry about buckling; things get messy.
Side face - Strength reduction could be minimal.

Rod Smith, P.E., The artist formerly known as HotRod10

 

[Ron]

If you want to try a weld repair you could do a hardness traverse across the heat affected zone after PWHT. That should tell you the affect of the welding.