stretching wire

[Mike Imbler]

As a mechanical engineer, I concur with Ron.  John's cite of the high tension electrical wires makes it clear that they are being tensioned beyond yield strength, which is why the article suggests heat treating the wire (which increases yield strength).  Yield strength is the point where the wire would plastically deform (stretch) which is less than ultimate strength (breaking stress).  Therefore, you -could- stretch piano wire, but you would be pulling it above its yield strength.  This would be more likely with more ductile wire which has a yield strength appreciably lower than ultimate.  With a more modern piano wire, yield strength is closer to ultimate.
              Mike 
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