Re: [Harp-L] Fatigue and reed life

["steve warner" <10reedsbent@xxxxxxxxx>]

Ductility!  The deciding metallurgical factor is  "Yield Point" and this
means how far a metal can bend before it  will not come back to it's
original state and the brass/bronze family is a good choice, in the old
world, but it's properties are limited.
I did alot of electrical work for high security military aircraft andI do
know for a ''fact'' that there are exotic metals that will outperform all
materials harps are made of in ductility, tensil strength, weight...etc ,
but it isn't feasible to use exotic metals for harp companies.   In the
business world they have to make them a consumable type product to keep the
"Machine" rollin'.  Dig?




On 4/17/08, Aongus MacCana <amaccana@xxxxxxxxxx> wrote:
>
> As I remember from second year engineering school, susceptibility of a
> material to fatigue failure  could be predicted by a "notch sensitivity"
> test. A test where an ingot of the material to be tested has a standard
> notch machined out of it and is given a whack by a standard pendulum to
> see
> what it takes to break it off at the notch.
> A fatigue crack is most likely to start at a surface imperfection or a
> sudden change in section of a component e.g. injudicious scraping with the
> tuning file or chisel (especially across the reed!)or at the junction of
> the
> base of the reed where it's section is reduced after the rivetting flange.
> This suggests that 'tuning passes' would be best made along the reed
> rather
> than across it and a rotary grinding tool might give less surface
> discontinuity than the regular file or scraper does.
> Hot rodders have a fetish for highly polishing highly stressed components
> like engine conrods to try and ensure that there are no surface
> imperfections or stress raisers to breed fatigue cracks. They also
> compress
> the outer surface of such components by shot peening them (bombarding them
> with steel shot)but this does not look like a feasible strategy for
> harmonica reeds.
> Aongus Mac Cana
>
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-- 
steve
www.thunderharpmics.com
fattest tone on earth!