Ultra-Tow aluminum trailer catastrophic failure

[foxwalker]

Hi All,

I built a 6’ W x 10’ L x 6’ H trailer on an Ultra-Tow aluminum 5’ x 8’ trailer back in 2017. It was made of 1” foam sandwiched between 1/4” ply with minimal 1” x 1.5” framing and weighed about 1,100 lbs - 1,250 lbs total depending on what I carried inside. It served me well at 4 Burning Man’s, a few weeklong trips around California and a handful of 2-3 night trips, until a couple weeks ago.

Before I headed home from a 2 night trip, I noticed that the front of the trailer was unusually low, making a shallow V between the wheels and the tongue. Inspection revealed that both tongue beams had cracked almost all the way through where the front crossbeam sat on them. The crack was a good 1/4” wide at the bottom, and just a 1/4” - 1/2” held it together at the top of each. I wish I had taken a picture then but I only took pics after I jacked up the frame to take all weight off the tongue. I can only be thankful it didn’t break on the freeway or in the middle of a road.

Long story short, I ended up giving it away to the property owners to use as storage because it would have cost me $1,800 to have it hauled the 120 miles home and I had no confidence that it could be repaired such that I’d feel totally safe hauling it around.

I realized later that the bed was at the very front of the trailer, so the tongue had that extra weight to bear when I and sometimes my girlfriend with me were sleeping in it. I always camped on flat ground and just left the tongue connected to the car or supported by the tongue jack and I never put support where the weight was, so it had support at the extreme ends with the weight in the middle. I should have supported the frame and taken the weight off the tongue.

Hard lesson learned. I’m now planning my next build, a pop-up or folding or collapsing foamie on a Karavan 5’ x 8’ steel trailer from Tractor Supply Co (the Ironton steel 5 x 8 from Northern Tool is out of stock till end of Aug darn it). I’ll be saving weight with the foamie but adding weight with the steel trailer, but should come out a little lighter than my previous build.

 

[S. Heisley]

Wow! Thanks for sharing this. You may have saved someone else from making the same mistake.
Best wishes on your upcoming build.

 

[scowan]

That could have been really dangerous.Worked in industrial maintenance that used lots of aluminum parts such as robotic equipment that had to be kept light weight.
Seen lots of fatigue cracks and failures.Sure some love their aluminum trailers but I would be leary.

 

[alaska teardrop]

The location & weight of the bed, I don't believe was the cause of the failure.

This is a quote by Andrew from another thread:
"Aluminium is a fine material - if you have years of experience of building trailers from it, or you have a team of aeronautical stressers to design it. For everyone else, it is a bit of a gamble.

Most trailers don't fail on one-cycle strength (one enormous load) but on fatigue strength (many little jiggles) when cracking starts. Most aluminium alloys have the disadvantage, compared to steel, that they do not have a fatigue (or endurance) limit, so even if the jiggles are tiny, if it is jiggled for long enough, in the end the aluminium will fracture. This graph from Wikipedia shows the effect:

Image

So in steel as long as the jiggles are less than about half the maximum strength, it doesn't matter if there are one million or one billion of them, the steel won't start cracking. But with aluminium alloys, there is no such limit.

DC3s were built before the much stronger age-hardening aluminium alloys (Duralumin was the first, I think) had been discovered, which is why many DC3s are still flying when younger planes aren't. It says diddly squat about the long term strength of an aluminium trailer frame.

Welders often like to quote the 'stronger than the parent metal' claim, but they rarely say 'failure will occur in the parent material in the heat-affected zone right next to the weld', as that isn't such good advertising. And they are talking about one-cycle strength, not fatigue strength, which is often much lower for welds.

The Australian trailer rules go so far as to recommend that tongues/A-frames are not welded to the front cross member of the trailer at the point where they cross it, so that the lower fatigue strength of the welds do not start cracking - and the Aussies have a lot of washboard roads, which are the ideal 'jiggler' to cause fatigue failure, so they have more experience of this than most.

Clearly, it is possible to build a strong, long-lasting trailer frame from aluminium, but it isn't guaranteed."
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[foxwalker]

Alaska Teardrop you're probably right but I think the extra weight at that point didn't help and probably helped it finally crack.

 

[Pmullen503]

Did the crack start at the bolt hole or the bottom? Was the hole there or did the user add it?

 

[GTS225-TNT]

You have learned what we in the performance and hot rod auto world are finding out. Aluminum radiators don't last either. Too many of us have removed that old and corroded brass/copper radiator in favor of aluminum, only to have the thing develop cracks and leaks 3-4 years later, due to vibration and stress, and have to be replaced, (usually by another aluminum one).

Me, I decided to spend the money to have my 60+ year-old radiator re-cored just last year. Tried and true brass and copper.
I suggest you, and we, all stick with tried and true steel in a structural frame.

Just my opine.....Roger

 

[kennyrayandersen]

It looks like that trailer could be easily over-loaded. That would reduce the fatigue life by a huge amount. Aluminum can certainly work, but it is less tolerant of abuse or improper sizing.