[Harp-L] Re: Re: Yellow Brass (was GM) (Vern)

["geoff atkins" <geoffatkins@xxxxxxxxxxxxxx>]

Vern asked Smo-Joe
"To what kind of waves do you refer, compressive waves or some kind of
higher-frequency mode of transverse vibration? How do you know that such
waves exist in harmonica reeds?  What is your source of this information?" 

My 2 cents worth:
I think we can all agree that a reed "vibrates" to make a sound, and that
the vibration is an oscillation of the reed extremity in both upwards and
downwards directions relative to its opposite fixing point, which is the
unmilled reed base and the rivet on the reed plate.

The reed can thus be classed as an unsupported cantilever, which in
positively-loaded cases experiences tensile forces on the upper surface,
zero forces at the neutral axis, and compressive forces on the lower
surface. 
On the second half of the oscillation's curve, the loading and resultant
stresses reverse: Compression top, tension bottom.
The tip is unstressed, whereas the fixing area is subjected to relatively
high bending moments:(load x length)^2 /2, (four times greater than if
simply-supported)...though there is probably some load shedding along the
reed.

Scratching a diagonal score in the area of the root makes the performance of
the reed more complex, but if it's directed more along the reed than
perpendicular to it, the score shouldn't cause a fracture. Whereas the
perpendicular variation in the material thickness at the root is a weak
spot, which can be relieved by a filleted radius of metal.

I've twice seen 12" diameter solid steel stub axles (on different machines
experiencing vibration) break because of unradiused variations in the
profile.

greetings and 98 cents left
Geoff Atkins