stretching wire

[John Delacour]

At 13:26 -0400 9/4/08, AlliedPianoCraft wrote:

>If the wire is not stretching somewhat, why is it we always need to 
>pull the pitch up and rarely down? If changing temperature and 
>humidity is the only cause for a piano to go out of tune, then we 
>should be dropping pitch as much as raising it.  I'm not saying your 
>information is incorrect, I just want to know why we just keep 
>pulling it up. Just how much can everything compress?

Every time this topic comes up, Ron Nossaman repeats his categorical 
assertion that steel wire is perfectly elastic within its normal 
elastic limit and that it  can therefore undergo no permanent 
elongation.   The contrary has been known to be the case ever since 
Vicat first did experiments to investigate this in 1830.

Here is what I wrote nearly a year ago on this topic:


At 7:47 pm +0100 27/4/07, John Delacour wrote:

>Love (A Treatise of the Mathematical Theory of Elasticity - 1926. 
>From Dover) cites a number of previous researchers and notes an 
>experiment by Vicat:- " He found that wires held stretched, with a 
>tension equal to one quarter of the breaking stress, retained the 
>length to which this tension brought them throughout the whole time 
>of his experiments (33 months) , while similar wires stretched with 
>a tension equal to half the breaking stress, exhibited a notable 
>gradual increase of extension."

<http://art-et-histoire.com/index4.php?segarch.php?>
<http://www.1911encyclopedia.org/Elasticity>



If you go to <http://patft.uspto.gov/netahtml/PTO/srchnum.htm> and 
enter number  4514237, you will read

This invention relates to the heat treatment of cold drawn carbon 
steel wire, for use more particularly in overhead transmission lines, 
whereby to reduce the susceptibility of the wire to permanent 
elongation when subjected to tensile stress.

Overhead transmission line conductors are subjected to severe tensile 
stresses when loaded with ice. In an ACSR (Aluminum Conductor Steel 
Reinforced) conductor the steel core takes a large part of the 
tensile stress and undergoes strain giving rise to conductor sag. The 
resultant strain is not wholly elastic and the steel core does not 
recover to its original length when the stress is relieved. In 
consequence the conductor acquires a permanent sag due to the 
permanent elongation of the steel core, and in a transmission line 
which has been subjected to heavy ice loading the resultant permanent 
sag may necessitate restringing of the conductors of the transmission 
line, which is a costly undertaking.

The applicants have discovered that this tendency to creep can be 
greatly reduced by suitable heat treatment of the steel wire, called 
ageing, the treated wire being suitable for use in overhead 
transmission lines...

JD
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