One of the things I treasured about the engineering department at one of the better universities I attended, was the off hand, throw away comments from the lecturers, these were always offered up without proof and often there was no proof, just informed supposition, with perhaps the hope that someone would provide the proof.
The other day the front suspension spring on my Skoda Yeti broke, I felt it let go and heard it as it bounced about under the car as we ran over it. I stopped to pick the broken end up. This brought to mind one of those throwaway comments: 'Coil springs alway break 3/4 of a turn from the end.' Sure enough 3/4 of a turn from the end is what I picked up. I have a few other pieces picked up off the road of similar sized pieces of spring. (Nice high carbon steel for forging, worth picking up.)
So does anyone have any idea why coil springs should break at 3/4 of a turn? My intuition says that half a turn is maximum stress.
Coil spring breakages
- Boustrophedon
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Coil spring breakages
Perit hic laetatio.
Re: Coil spring breakages
3/4 of a turn is 90 degrees around from your assumed maximum stress point, so maybe that's the point that gets torsionally worked back and forth the most? Or is your half a turn already that point?Boustrophedon wrote: ↑Wed Aug 03, 2022 10:11 pmOne of the things I treasured about the engineering department at one of the better universities I attended, was the off hand, throw away comments from the lecturers, these were always offered up without proof and often there was no proof, just informed supposition, with perhaps the hope that someone would provide the proof.
The other day the front suspension spring on my Skoda Yeti broke, I felt it let go and heard it as it bounced about under the car as we ran over it. I stopped to pick the broken end up. This brought to mind one of those throwaway comments: 'Coil springs alway break 3/4 of a turn from the end.' Sure enough 3/4 of a turn from the end is what I picked up. I have a few other pieces picked up off the road of similar sized pieces of spring. (Nice high carbon steel for forging, worth picking up.)
So does anyone have any idea why coil springs should break at 3/4 of a turn? My intuition says that half a turn is maximum stress.
- Boustrophedon
- Stummy Beige
- Posts: 2900
- Joined: Mon Nov 11, 2019 3:58 pm
- Location: Lincolnshire Wolds
Re: Coil spring breakages
I don't know really. A very rigid thick coil spring could be loaded at just the tips of the spring and such an asymmetric load would give a maximum stress at 1/2 a turn in, but a real flexible spring bends and settles and perhaps a portion of the end of the string lies flat on the spring seat, moving the maximum load round the coil a bit.
Perit hic laetatio.
Re: Coil spring breakages
A Google image search for Broken Coil Spring shows a variety of break points; maybe people say anything between 210 and 330 degrees is 'about 3/4', and if you do that you'll up the percentage for which that's true.
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IANAE
My avatar was a scientific result that was later found to be 'mistaken' - I rarely claim to be 100% correct
ETA 5/8/20: I've been advised that the result was correct, it was the initial interpretation that needed to be withdrawn
Meta? I'd say so!
ETA 5/8/20: I've been advised that the result was correct, it was the initial interpretation that needed to be withdrawn
Meta? I'd say so!