Elastic limits,

[Richard Moody]

	If the values for  elastic limits are the same as the yeild point,
Jim's chart shows that you can take the tension to 86- -88 percent of
the breaking point before you cause string elongation.  If that fits
the definition of elasticity limit, as Jim puts it, "the limit a
string can be stretched and yet return to its original length."
	By scale tension calculation it appears that makers are running 80
to  100 + pounds under the elastic limit. ( in unwound strings at
least) .  This would seem to give a cushion to those of us who like
to do things that exceed the pitch tension such as chipping sharp,
pulling replacements sharp, using the "string stretcher" p19 Schaff
Tool Catalog, False Beat Suppressor, p.21, and other practices such
as thumbing a string to slightly flatten it while tuning, or seating
strings from the outside of the bridge, and last but not least,
string leveling.
	How much extra tension are we putting on the strings?  I assume the
use of vectors should give the answers, but I havn't been able to
figure out elementry problems such as.

	A ten pound force is applied to a piano string in the middle. How
much is the string's tension increased?  The length is 30 inches, the
tension is 180 lbs.  (750mm, 81.81kg)     10lb = 4.545kg.  If the
distance the wire is deflected must be known, calculate for every 2
mm, or 1/8 inch.

	A string is depressed 3/8 inch in the middle.  (10 mm) How much
tension is the string now under?  Length 30 inches, tension 180 lbs.
How does the tension change at 2 inches from the bridge, 4 inches, 10
inches.

Can these problems be solved by vector addition.  If so how?

Richard Moody



----------
> From: Jim <pianotoo@IMAP2.ASU.EDU>
> To: Richard Moody <remoody@easnetsd.com>
> Cc: pianotech@byu.edu
> Subject: Re: Elastic limits,
> Date: Sunday, April 27, 1997 2:29 AM
>
>  The Parson PScale program computes this elongation in order to
> let the designer have full control of the unwrapped lengths which
have so
> much to do with the final inharmonicity of the Bass strings.
>
> Jim Coleman, Sr.
>
>
> > > >wire size    yield point    break point
> > > >
> > > >13           258 lbs        290
> > > >13.5         267            303
> > > >14           317            355
> > > >15
> > > >16           347            398
> > > >18           431            487
> > > >
> > > >