Taken from :
Today at work we finished up the absolute worst failure investigation I, or anyone else, could ever remember doing. The failure was an older “mag” type two-piece wheel. The outer rim section failed during the tire mounting process. The person doing the mounting was a seventeen year old kid. A section of the rim broke off as he was “popping” the new tire’s beads into place. The rim section came in just to the right of his throat and came out by way of his spine. The only good thing is that he died instantly.
The cause of the failure was threefold, and this is why I’m posting up about it.
- At some point in the unknown past, the wheel had cracked circumfrentially along the inner edge of the spun section. This crack was due to fatigue, originating doubtless from countless slight flexings of the wheel as it was driven over bumps and around corners.
- The owner of the wheel had it “repaired” after this crack was discovered. This consisted of a circumfrential weld over the crack. The wheel, which was aluminum, was not heat treated after this was done.
- The crack continued to spread and weaken the wheel, aided and abetted by the locally softer material in the vicinity of the weld.
Eventually, the wheel became weak enough that the 40-ish PSI it was subjected to during the mounting process that it failed, explosively. When we did scanning electron microscopy of a section of this wheel, we found blood molecules all over it.
What I have to say is this:
Those of you with lightweight wheels, race wheels, or just wheels that you race on, please do us failure investigators a huge huge huge favor so that we never have to see this kind of thing again.When your old tires come off, clean the wheel and give it a good look over for cracks of any type or description. Do this as often as possible, but at least once a year. If you even THINK you have cracks, don’t screw around. If you’re not sure, you can contact me, and I’ll dye-check it for you. I’ll do this at my expense, even.
When or if you find cracks, don’t use it for anything except an end table. Ideally, give it a flotation test: take it to the nearest large body of water, and throw it in. If it floats, consider salvaging it. Cracks in cast or forged aluminum CANNOT be realistically repaired. Welding just makes matters worse, it just puts a cap on top of the crack and then encourages it to spread by locally annealing (softening) the material. Furthermore, don’t send a wheel to be repaired for dings either. Minor ones aren’t a big deal, but cast aluminum doesn’t like to be bent, let alone bent back. Even worse, the way people invariablly try to fix it is to heat it with a torch and then hammer it back into shape. As you can guess, all you have done is to make that section of wheel signifigantly softer and weaker than the rest of the wheel.
I know that this post is lo-ng and apropos of nothing, but I’m sorry, I NEVER NEVER NEVER want to do this kind of investigation as long as I live. Do me a favor, huh?
:meh:
:lolsign: