STME58
198 posts
Jul 05, 2012
2:28 PM
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These images are from the 7 blow reed of a Honer Special 20 that went flat. At first I could not find the defect, even under the microscope. I flexed the reed and felt it give and then the cracks became evident.
This failure is closer to the root where a cantilever beam analysis predicts failure wil occur when the beam is loaded with constant pressure. A previous Seydel reed I posted a phot of failed where a modal analysis predicts failure will occur when the reed is vibrating at the first resonant frequency.
It does not surprise me that reeds fail by
different mechanisms, or that my styles of playing hit multiple mechanisms of failure.
I managed to replase the reed in the Special 20 and it is in tune but it sounds week at low volume compared to the other reeds. The gap at the tip and along the edge look ok but something is not right.
Last Edited by on Jul 05, 2012 9:47 PM
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ReedSqueal
300 posts
Jul 05, 2012
4:39 PM
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I would think cyclic fatigue failure, but on a 7 blow reed? Put a cross section of the fracture surface in a scanning electron microscope and I'll bet fatigue striations are present.
Wondering if there was a flaw in the reed somewhere, either mechanically induced (i.e. corrosion or a nick, somewhere near at at the point of origin of the crack) or perhaps at the metallurgical level. (i.e. inclusions of some sort)
or something like that.
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Go ahead and play the blues if it'll make you happy.
-Dan Castellaneta
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STME58
199 posts
Jul 05, 2012
9:52 PM
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I don't know if I can get acess to and SEM but it is a possibility. It does look like the crack started at the top edge in the top photo and propagated across.
The crack does seem to be right at the end of the radius from the thick anchor end of the reed down to the main vibrating part of the reed. This is the highest stress point when the reed is uniformly loaded. As it woule be under air pressure and before it starts vibrating.
When these cracks happen the reed goes flat fast. I have retuned reeds after this happens and they won't hold a tuning for 5 minutes. You can tune them back up and they losse it quickly again. It is odd that they only go down to the pitch of the draw reed, or perhaps they quit sounding and the draw reed sounds on a blow.
this is the same reed. No information here about the failure but it does show the reed profile. This is just that way honer set it up as I had done no shaping or gapping on this. There is quite a noticable taper. the reed gets thinner toward the tip.
Last Edited by on Jul 05, 2012 9:57 PM
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