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

[Vern <jevern@xxxxxxx>]

Atkins has summarized the source of stresses in harmonica reeds as I understand it... but without addressing the questions in my previous post. 
On Mar 9, 2010, at 10:01 PM, geoff atkins wrote:

> 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.

Yes, alternating displacements and stresses but there are no waves within the reed.  
> 
> 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
> 
>