Woody 2

Here's the wooden tube and a section of alu seat tube after being taken to failure

You can hardly see a mark on the wood but the alu tube is clearly dented.

Now for the interesting bit. What were the results? I did quite a few tests but have distilled the results into this graph

The sharp eyed will spot that the curves should be linear at the start (before the samples have yielded) I think the odd shape os probably due to my highly non technical test rig and some 'bedding in' movement that happened in all the tests (the foot pad is slightly spongy!)

The alu tube failed at a much higher force than the wooden tube, which dissappointed me as i was expecting it to perform better. I've also plotted the 'reload' curve after I reloaded the wooded tube several more times. It performed reasuringly (suprisingly) similarly under smaller loads despite having clearly failed in the first test.

However, I spotted something quite promising. What if we're not interested in the size of the impact force, but rather the energy of the impact. This would be equivalent to dropping something on the frame, or dropping the frame on something and absorbing the impact without damaging the frame. The energy absorbed by the tube is the area under the curve, which, is considerably larger for the wooden tube.

So, despite failing at a lower load, the wooden tube can actually withstand a larger impact because it is more flexible and deforms more enabling it to absorb more energy.

What this does not show is the post yield energy absorption as the alu tube would have a much better post yield behaviour.

I'd love to do the same for a carbon tube to see how it compares.

Anyone got a write off frame that I can cut up and test?