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轉寄: Alloy Frame testing – crack and FAIL!
Because of the tough new CEN legislation for frame strength, we test all our frames on violent test rigs, not to MEET the standard, but to easily EXCEED it.
We started the testing with the alloy frame with the most difficult step for an alloy frame – the fatigue test for pedaling forces. The target is 100000 cycle, but the frame cracked at 69137 cycles.
From the photo, the crack from the seat tube, the seat tube thickness is 1.6mm at the base, and to start with, we thought maybe we should hoik up the wall thickness to 2.2mm. But then, we looked closer, and we give up this idea, because we find the key point .
To make this joint, normally the factory cut the tubing according to the joint angle, then put BB, D/T, S/T, H/T ,TT at same tooling, clamping all parts, and point welding. Then welding whole circle. This is how most alloy frames are made. For normal thickness tubing, this way is ok, but for thin tubing, we must make the seat tube joint to the BB much stronger.
So – to fix this, we’re going to do this. Do it right. We will keep the same tubing spec. But first, we weld the seat tube to the BB. After that step, we just can put ( BB+S/T) + DT+TT+HT together at in the jig for more welding. Our factory already use this kind processing for lightweight alloy racing frames, but this time the welder must have looked it as a sample and didn’t follow the standard step.
So – there’s new version being made now, but we thought you’d like to see the cracked one, so you can see why we try and do things better, do ’em right, and do ’em without just throwing more metal at the problem.
shedfire
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Adrian 8:20 am on May 4, 2009 | #
where did the crack start? it looks like the undercut of the weld on the rear of the seat tube.
Jon 11:37 am on May 4, 2009 | #
Any photos of the whole frame?
ChrisL 3:46 pm on May 4, 2009 | #
Is the 100,000 cycles target your target, or the CEN requirement?
shedfire 3:49 pm on May 4, 2009 | #
100,000 is the CEN standard in this case. Then we keep the machine running.
ny 4:39 pm on May 4, 2009 | #
Does the Ti frame go through the same CEN testing? How did it fare?
shedfire 6:03 pm on May 4, 2009 | #
The Ti frame is built to CEN specification by Lynskey, though we haven’t specifically jiggled one on the jiggling machine. Though I think we probably will.
weightweenie 9:32 pm on May 4, 2009 | #
It looks the boat anchor weight doesnt help! WHo is the wan*er now? 😀
shedfire 9:34 pm on May 4, 2009 | #
Ah – but the weight isn’t going to alter and it’s going to be twice as strong – w*nker 🙂