Failure Testing

Posted: April 20, 2012 in Uncategorized

My #1 goal when building a bicycle frame is to ensure that it is a safe vehicle that provides a lifetime of quality service.

I use TIG welding because it is a very reliable way to produce an extremely strong joint.

This afternoon I decided to destroy an old frame that I built several months ago. It was actually the forth frame that I ever built but I have since decided I have no interest in a fixie track bike for my personal stable and as such the thing was just taking up space.

For my destructive testing I started with my car jack to apply a twisting force to the headtube. The frame bent a lot but did not crack and at the end the jack actually broke (this will suck when I get a flat in the car).

Plan “B” for the destructive testing involved cutting the frame apart, welding some extra tubes on and then using a big threaded rod to apply a crushing force. With this approach I was able to get the top tube to collapse at the butting transition zone but even after all this the frame did not crack. If extreme forces like this occur in the real world I am very confident that the frame would bend rather then fail all at once. I am 100% sure that had this frame been ridden it would be safe.

Enjoy the photos…

My first try was to use a car jack and some threaded rod. The result was that the car jack broke and the threaded rod was bent. The frame was also bent but only slightly. It would still be possible to build up the frame and ride it and none of the welds were damaged.

The rod and frame were only slightly bent, one thing for sure is that the car jack was really poorly made. When it failed the jack collapsed and honestly I would not have wanted to be under a car with such a jack.

For my next try I reworked the frame by cutting it and rewelding it so I could apply force to the headtube joint using the threaded rod.

Using the threaded rod approach I was able to cause the top tube to bend. The tube buckled but did not crack. The bend occurred at the point where the butting makes the tube thinner and this is where I expected to see failure. The downtube is stronger and did not seem to bend because with this testing the two tubes were fighting each other. The welded joint was fine with no damage.

I also bent the chainstay and once again the tube bent and the joints were fine.

I cut out the bent section to confirm that the bend was at the point of the point where the butt transition occurs.

As with other tests that I have done this gives me confidence that my processes are sound.

Comments
  1. MattB says:

    It would take a lot to replicate those forces in real world riding.
    I’d say you’re right to be confident in your building from the pictures alone.
    Hope you had fun!

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