stretching wire -- an anecdotal analysis

[Richard Brekne]

Whoa there JD... keep your pants on.  I didnt take any standpoint one 
way or the other outside on making an observation about what I 
understand the discussion to be (at least) partly about.  Some 
participants seem clearly to have raised the possibility of a string 
yielding over time despite being well under yield limit... others 
(apparently in the majority) refute that.  The links were provided only 
to provide a general background for what some of the terminology was as 
it seemed clear that a few in the discussion were mixing up this that 
and the other concepts.  That said... nothing in those links are not 
easily applicable to the case of steel  music wire. The links simply lay 
out definitions for terminology.

Cheers
RicB


    JD writes:

         >Richard Brekne wrote:
         >The question being thrown around here (as I understand it)  is
         >whether or not there is any plastic creep over long time when the
         >wire tension is kept well below this level of stress.


    Well, let me dissociate myself from any such analysis.  I don't know
    what "plastic creep" is and I am not interested in what happens to
    wire once it has passed its limit of elasticity.

         >Richard Brekne wrote:
         >The following link may also be helpful, as it goes directly to the
         >question of whether a string can experience plastic
        deformation despite
         >being well under yield strength limits.
         >
         >http://en.wikipedia.org/wiki/Creep_%28deformation%29


    There is no mention of steel in the whole article and it is pretty
    clear that "creep" is not a phenomenon that occurs with patented
    steel wire or, probably, any steel wire.

    If piano wire subjected to high tension _within_ its elastic limit
    gets longer over a period of days or weeks as it accommodates itself
    to the tension, then that has nothing to do with "creep" or
    "plasticity".  If you take patented steel wire beyond its elastic
    limit, it will neck and break, perhaps right now, perhaps tomorrow
    but very soon.  Whatever other people are talking about, I am not
    talking about such a case.  The case I am talking about is that, for
    example, of a length of No. 17-1/2 wire (1 mm) at a tension of 200
    lbs, a high tension but safe for this wire, and the question  is :

    a) If constant tension is applied to the wire, will it, over a period
    of days get longer and then gradually settle down?

    or, which comes to the same thing,

    b) If 200 lbs tension is applied to the wire stretched between two
    fixed points, will the tension fall over a period of days and then
    settle down?

    Experience leads me to think the answer is yes, but without an
    experiment that completely eliminates all the other causes for pitch
    drop in a piano, which have been mentioned in this thread, it is
    impossible to say it is so.  I have now devised an apparatus that
    will enable me to carry out tests and hope in the next few days to
    get the thing set up.

    JD