<!doctype html public "-//W3C//DTD W3 HTML//EN"> <html><head><style type="text/css"></style><title>Re: stretching wire</title></head><body> <div>At 13:26 -0400 9/4/08, AlliedPianoCraft wrote:</div> <div><br></div> <blockquote type="cite" cite>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?</blockquote> <div><br></div> <div>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.</div> <div><br></div> <div>Here is what I wrote nearly a year ago on this topic:</div> <div><br></div> <div><br></div> <div>At 7:47 pm +0100 27/4/07, John Delacour wrote:</div> <div><br></div> <blockquote type="cite" cite>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."</blockquote> <div><br></div> <div><http://art-et-histoire.com/index4.php?segarch.php?></div> <div><http://www.1911encyclopedia.org/Elasticity></div> <div><br></div> <div><br></div> <div><br></div> <div>If you go to <http://patft.uspto.gov/netahtml/PTO/srchnum.htm> and enter number  4514237, you will read</div> <div><br></div> <div>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.<br> </div> <div>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.<font color="#AA0000"><b> The resultant strain is not wholly elastic and the steel core does not recover to its original length when the stress is relieved.</b></font> 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.<br> </div> <div>The applicants have discovered that<font color="#AA0000"><b> this tendency to creep can be greatly reduced by suitable heat treatment of the steel wire</b></font>, called ageing, the treated wire being suitable for use in overhead transmission lines...</div> <div><br></div> <div>JD</div> </body> </html>