Re: [Harp-L] breaking in marine bands (metal fatigue; a definition)

["Vern Smith" <jevern@xxxxxxx>]

----- Original Message ----- 
From: "Paul Bowering" <paul_bowering@xxxxxxxxx>
To: <harp-l@xxxxxxxxxx>
Sent: Tuesday, August 16, 2005 11:28 AM
Subject: Re: [Harp-L] breaking in marine bands (metal fatigue; a definition)


> >"Some materials, for example steel and titanium,
> > exhibit a fatigue limit, a limit below which repeated
> > stress has no effect. Most others, for example
> > aluminum, exhibit no such limit and even
> > infinitesimally small stresses will eventually cause
> > failure."

I think that the statement that "infinitesimally small stresses will 
eventually cause
failure" isn't warranted.  As the stresses approach zero, the fatigue life 
approaches infinity in a non-linear fashion.  None of the published data 
deals with very small stresses because they aren't relevant to the uses of 
metals in real machines...a harmonica is a machine.

> One side question related to this issue. What other
> signs beside a sudden drop in pitch point to a reed
> that has suffered metal fatigue?

None that are apparent to the player.  If you could examine polished and 
acid-etched surfaces or cross-sections of the reeds under a microscope, then 
you might be able to see tiny cracks at the grain boundaries that are 
precursors of fatigue failure.

Vern