Tail wheel cold weld

[snoop9erdog]

Originally Posted by JonJay

I the only time I have done a die penetrant it has been on bare metal. Would it not require you to strip any coatings off before using this kit?

Correct Jay, for best results the weld area neds to be cleaned and clear of paint, coatings, etc. Keep in mind that you are only going to discover surface irregularities/cracks and not penetration information...but the crack information is obviously useful for eventual failure.

[JonJay]

Originally Posted by snoop9erdog

Correct Jay, for best results the weld area neds to be cleaned and clear of paint, coatings, etc. Keep in mind that you are only going to discover surface irregularities/cracks and not penetration information...but the crack information is obviously useful for eventual failure.

Well, I hope to see the crack through the paint before it fails, if it ever does, as I am not going to strip off the paint and repaint my tail post to do a die penetrant check.
If it ever does fail, I guess I will have a skid to land on. I bet a skid would keep the tail behind me quite well!

[DavidBurton]

It would be interesting to see some well focused, close up photos of the failed weld areas. The fractured surface tells us how the weld failed. It could be in tension with a good ductile failure. This might indicated that the weld was done using a correct process but with a failure to achieve good penetration or large enough fillet. If the weld penetration is poor, a "failure to get the root out" there is a notch at the base of the weld that will be a crack initiator. You can read a discussion of a failure analysis caused by this here:

http://www.met-tech.com/crane-weldment-failure.html

If we see a brittle failure this could indicate poor filler material selection or poorly designed welding process.

Fatigue failure points to poor technique, poor materials selection and incorrect process.

When developing a welding procedure on a critical weldment it's common to analyze test components by doing cross sections and at least visual analysis of the welded parts. Unfortunately too many welders assume that globbing some filler material between the two parts they want to join will be sufficient. This became such a huge problem with mechanics welding trailer hitches on to car and truck frames without having any idea of what they were doing that the DOT banned this practice unless done by a certified welder. It's likely that the certified welder's insurance company prohibits the welder from doing it anyway.

If the welding process builds up too little heat or adequate filler material the thick tubing will quench the weld causing it to become brittle. Often an inexperienced welder will choose a welding rod that is much stronger than the base materials in an attempt to make a "stronger" weld. The much stronger filler material will not be ductile as compared to the base material and this can initiate a cracking caused by stress concentrations in microscopic areas adjacent to the weld leading to fatigue failures.

Just being a proficient welder doesn't insure that the finished weld will be satisfactory. A well designed welding process based on the materials and anticipated loads expected is necessary. If the loads are cyclic in nature like those experienced by this weld it is extremely important that the process developed insures that fatigue failures are prevented.

David
Metallurgist, destructive and non-destructive material testing engineer, forensic failure analyst and American Welding Society QC1 certified welding inspector.

[Mike S]

Originally Posted by DavidBurton

David.

Metallurgist, destructive and non-destructive material testing engineer, forensic failure analyst and American Welding Society QC1 certified welding inspector.

The breadth and depth of knowledge available here never ceases to amaze me.

[gmpaul]

Originally I posted this to see if anyone else has had a WD-101 break.
So far it seems there is just one other (#35).
I am in communication with Vans and they want to make everything right (which I knew they would) since they are such a great company.
They requested the broken part and it should be in their hands next week.
I will post after I hear back from Vans.

G.P.

[Bob Kuykendall]

Originally Posted by DavidBurton

It would be interesting to see some well focused, close up photos of the failed weld areas...

I definitely agree. But I would also like to see a free-body diagram that analyzes the stresses within the weld that prevail as the tailwheel passes backwards over a 1.25" obstuction. My suspicion is that this loading case gets close to the yield stress even for a properly-done weld.

[JonJay]

Originally Posted by Bob Kuykendall

I definitely agree. But I would also like to see a free-body diagram that analyzes the stresses within the weld that prevail as the tailwheel passes backwards over a 1.25" obstuction. My suspicion is that this loading case gets close to the yield stress even for a properly-done weld.

A properly done weld should not yield. The material around it might but the weld should not. If it does, there is something grossly wrong with the design of the part. With thousands of these tail wheel posts backing over hangar door tracks for many years, I think we would have seen more than one or two failures.
I inspected mine last night. The weld beading was significantly different than the photo's shown of the broken parts. Much wider bead and penetration evidence (material caving) along the sides of the weld.

[vfrazier]

Originally Posted by rocketbob

Rewelding will shrink the ID by a considerable amount. Usually when welding stuff like this if it can't fit back in the jaws of my lathe I set my mill up with a boring head/bar and shave a few thousandths off the ID to true the hole again.

The bushing should be pressed out to reweld. If its an oillite bushing have fun welding if its still in there, they tend to catch on fire readily.

We weld these all the time after machining the I.D.s and have no issues with welding shrinkage on these thick walled parts. After welding, we also 100% inspect them just to make sure.

Properly done, the tailspring and the socket will make a "gas-tight" seal. You can feel the air compress when you insert the tailspring, and you get a nice "pop" when you pull it out.

Don't weld with the bushing in place. As Bob pointed out, they don't take kindly to the heat.

[gmpaul]

Here is the reply I received from Vans today (We have refunded your c/c for the defective weldment. Our apologies for
the trouble.
Credit $74.00)

[Skykingbob]

Originally Posted by DavidBurton

Just being a proficient welder doesn't insure that the finished weld will be satisfactory. A well designed welding process based on the materials and anticipated loads expected is necessary. If the loads are cyclic in nature like those experienced by this weld it is extremely important that the process developed insures that fatigue failures are prevented.

David
Metallurgist, destructive and non-destructive material testing engineer, forensic failure analyst and American Welding Society QC1 certified welding inspector.

David.....that was very interesting.....GREAT INFO......thanks for taking the time to post and link....I love this stuff!!!