Weld Strength: 6061-T6 Aluminum Forklift Pocket Weld

[laforzadiment]

Hello again PF

I am trying to find the failure load for a 6061-T6 Aluminum forklift pocket weld with 4043 filler. Can I simply multiply the cumulative throat area by the ultimate yield strength of the filler for this value? I never had any formal education on welds, wasn't sure if I'm missing something here.

This is a dual fillet weld failing in the transverse direction similar to the middle picture shown below. This data is pretty available for steel but I can't find any charts on aluminum.

Thanks!

 

[edgepflow]

You would multiple the throat area by an allowable stress which will be less than the ultimate yield strength: allowable stress = yield stress / safety factor.

The safety factor is greater than 1 and depends on many factors.

See "Design of Welded Structures" or similar reference for AISC allowable stresses for weld metals.

 

[laforzadiment]

Since the item has been manufactured and exists + it has failed, my safety factor would just be 1 to find the value of the load, correct?

If i have a 6 inch weld (along the length of the pocket, connecting the bottom to the right side) with a throat of 0.25, I have a throat area of 1.5 in^2. This means using the above method, if the yield strength of 4043 is 20 ksi or whatever that I'm looking at 30,000 lbs to fail a single weld? That can't be right. The forklift doesn't even weigh over 10,000 and isn't going fast enough to impart a force that high.

Help :-X

 

[yster]

that is the very reason why safety factors are used. Nothing made by a human being is perfect. Are you sure you Diego't get fatigue failure?
I ask because fatigue can result in sudden failure.
I would also use a safety factor of one for your situation but that would only give the ideal load at which it would fail if everything was perfect.
A number of aspects affect the true strengt of the weld so you can never bed too sure. From my experience with tig welding aluminium, it's not the easiest material to weld.

 

[DickL]

First off, I'm far from being an expert in either welding or failure mechanics/analysis, but failures are rarely as simple a mechanism as a lab test. First off give the failure site a very good examination. Look for signs of fatigue failure, crack growth, weld tearing, failure through the weld's throat or at the bonding surface, corrosion, lack of weld penetration, inclusions, failure initiation sites, etc. It is not unusual to find more than 1 suspect condition around the failure area.

Was the weld closed or finished off across the ends of the piece, or was it left as simply 2 filet welds ending along the length of piece. Not completing the weld around the ends provides a site for many bad things to happen, corrosion, stress risers.

If you can determine the failure mechanics, then you may be better able to estimate the forces involved, or figure out the appropriate corrective actions.