[Harp-L] Re: Breaking in Marine Bands

["Jonathan Metts" <jonathan@xxxxxxxxxxxxxxxxxx>]

>Is there a physicist in the house?  ;-)
>
>Steve

More importantly, is there a structural engineer in the house?  I'm not one, but I have taken some classes in the field and have access to a couple of professors who can probably answer this question.  From what I remember in my Structures classes, metals generally do not experience degradation from repeated loadings as long as those loadings remain within the "plastic deformation region", that is, the loads are not so great that they permanently deform the metal.  When you regap a reed, you are causing non-plastic deformation because the reed's shape is permanently changed.  When you blow or draw across the reed, you are causing plastic deformation because the reed's shape goes back to its previous state once you stop the airflow (load).  This all goes for aluminum alloys at least, because those were the focus of my coursework, but I'm pretty sure the concepts work for brass as well.  My professor will be able to confirm.

I remember be astonished in that class that there was no mention of long-term changes in the metal even when the loads are always in the plastic region.  So I asked my professor at the time, and he said there is a phenomenon known as "metal fatigue" that is related to the frequency of loading.  However, metal only fatigues under certain temperature and humidity conditions, usually underwater.  It is certainly possible that the humidity of our breath puts the brass reeds in such a wet environment that the reeds can fatigue over time.  As I said, I'm going to ask some people smarter than me this week and get a more confident answer for us all.

Jonathan Metts