stretching wire

[Ron Nossaman]

> I don't think this degree of plastic deformation stands in
> the way of the "strings don't stretch over the long term"
> idea.  First, keep in mind the amount of stretch cited
> here.  Even at the 300 pound tension, the plastic
> deformation was given as about 5 thousandths of an inch. 
> Maybe significant in some way, but it sure wouldn't account
> for any "winding up of wire on the tuning pin."  I don't
> know the pitch change for an increase in wire length of 5
> thou for 17 ga wire, but maybe our scaling guys can tell
> us.  I would enjoy knowing.

At 200lbs and 6" in length, about a semitone by my calcs. It's
pretty significant, but if it happens immediately as it's
pulled up to pitch, it's a non event from our perspective.


> More to the point, when did this plastic deformation occur,
> i.e., how long was the wire left tensioned?  I tried wading
> through this study, but didn't find the methods outlined
> very well.

Not to mention that 0.0374" wire is 16.5 gage metric now. Have
the gages changed since this was done? Moot point, since the
direct measurement is included.


> It appears the wires were only tensioned for a short period
> (less than a day).  In other words, this plastic
> deformation of music wire occurred _as the wire was 
> initially brought to tension_, and stayed there for the
> duration.  It does not conclude that the wire continued to
> deform over any length of time.

Correct, which is the point in question.

Again:
> This is from Mechanics of Materials, by Larson & Cox,
> published by John Wiley and Sons, 1947
> 
> "When an elastic material, such as steel, is loaded at
> ordinary temperature, it deforms in proportion to load
> almost simultaneously with the loading. Thereafter, the
> load may apparently act on the material for an indefinitely
> long period without causing any further appreciable change
> in dimensions. Even if the material is stressed above it's
> elastic limit, after an immediate deformation there appears
> to be no further change in dimensions until there is some
> change in load."


> So, for our purposes, this study seems to suggest that as we chip or
> raise pitch, there is bound to be some plastic deformation,
> but that once tensioned, no more deformation occurs over the long-term.
>  So, the theory that strings stretch over the long-term does not seem to
> be supported by this study/information.
> 
>  William R. Monroe

That's my take as well. But thanks, Dean, for the reference.
Ron N