Re: [Harp-L] Re: Reed Stress and Temperature

[Mike Wilbur <mike@xxxxxxxxxxxxxxxxx>]

Really ?.....that's not what I have witnessed but ok science wins.

Mike Wilbur

> On Sep 24, 2014, at 9:30 AM, patpowers <patpowers@xxxxxxx> wrote:
> 
> Thanks Vern, very good explanation.  I did a little research on Young's Modulous and you are 100% correct, the elasticity of brass actually increases at lower temperature. ..go figure!  Thanks for the education - I guess I won't be wasting time warming up my harps to breath temperature any more.
> 
> Thanks, and Keep Harpin'!
> Pat Powers
> 
> 
> 
> ----- Original Message -----
> From: "Vern" <jevern@xxxxxxx>
> To: "patpowers" <patpowers@xxxxxxx>
> Cc: "Larry Sandy" <slyou65@xxxxxxxxx>, harp-l@xxxxxxxxxx
> Sent: Wednesday, September 24, 2014 1:23:27 AM
> Subject: Re: Reed Stress and Temperature
> 
> 
>> On Sep 23, 2014, at 3:52 PM, patpowers <patpowers@xxxxxxx> wrote:
>> 
>> Thanks Vern - I love a good debate! ;)
>> 
>> ââ.., but my point is all materials get stiffer, and lose elasticity, as temperature decreases.
> 
> They gain elasticity (the value of E goes up) as the temperature decreases.
> 
>> And, I wouldn't necessary dismiss a 50ÂF to 80ÂF change in temperature as negligible.
> 
> I didnât say that a 30 degF temperature change is negligible but that the effect on pitch is negligible.
> 
>> On the flip side, I wouldn't consider brass to be brittle at 50ÂF either, but it is less elastic than brass at 80ÂF, especially when stressed and already fatigued.
> 
> As above, it is more elastic (higher value of E) at lower temperature.  i.e the restoring force is greater with equal deflection.
>> 
>> Regarding your statement "Reed behavior that concerns us takes place within the elastic zone below the yield point."  If this were entirely true, then reeds would never fail.
> 
> Reeds can fatigue and fail without ever being cycled at stresses as high as the yield point.  The yield point is that stress that will produce a permanent deformation. You exceed the yield point when you change the gap.
> 
>> Obviously the elasticity eventually diminishes to the point where the behavior exceeds the yield point.
> 
> The elasticity ( value of E) is a property of the metal and does  not change with time.  When a reed fails in fatigue it cracks and that is what changes the stiffness and causes it to go flat..
> 
>> At some point the metal fatigues and fails, and I still say colder temperature will accelerate this process.