<!doctype html public "-//W3C//DTD W3 HTML//EN"> <html><head><style type="text/css"></style><title>Re: stretching wire -- an anecdotal analysis</title></head><body> <div>At 21:20 -0500 19/4/08, kurt baxter wrote:</div> <div><br></div> <blockquote type="cite" cite> <blockquote>If you take patented steel wire beyond its elastic<br>   limit, it will neck and break, perhaps right now, perhaps tomorrow</blockquote> <blockquote>  but very soon.<br> </blockquote> </blockquote> <blockquote type="cite" cite>The point when when you go from "elastic" to "plastic" is when the wire<br> permanently changes shape, never to return, right?</blockquote> <div><br></div> <div>Yes, and with patented wire this point is very close to the breaking point</div> <div><br></div> <blockquote type="cite" cite>So I would say that when a string bends around the tuning pin, and<br> for sure when it dives into the becket, it changes it's shape for good.<br> <br> If you slightly "kink" a wire, you have taken it to it's plastic point... right?</blockquote> <div><br></div> <div>Yes and no.  When you make the becket on the wire the part near the outside corner is weakened but the core and inside corner are, if anything strengthened by compression.</div> <div><br></div> <blockquote type="cite" cite>So if a "kink" type load can take the string beyond it's elastic point<u> without breaking</u>, why not "stretching" type load?</blockquote> <div><br></div> <div>Also when the wire is initially coiled or when I straighten it for stringing or making bass strings it takes a permanent set.  Exactly what stresses are involved I can't say, but experience suggests they are not detrimental.</div> <div><br></div> <div>When I (or others) make bass strings I flatten the wire with a hammer and die to hold the copper at the ends.  If a string is stretched to breaking point it will never break at the flattening but either at the eye or at the becket or some point of friction UNLESS there is a sharp angle at the ends of the flattened portion.  When I had my first flatteners made 25 years ago, which I still use today, we got a chamfered end on the flattening that created too sudden a change from the flattening to the cylindrical wire and this caused a severe weakening.  Once we had ground off and radiused the top corner to the die, there was no problem.</div> <div><br></div> <div>These things do cause work-hardening and it's quite likely that the flattening process actually increases the tensile strength of the wire, but when we simply stretch the wire I think there is no work-hardening</div> <div><br></div> <blockquote type="cite" cite>Isn't there a big difference between "elastic limit" and ultimate limit?</blockquote> <div><br></div> <div>As I've mentioned before, some people use the manufacturer's UTS as the datum and take care not to strain the wire beyond 55% of this and others, like me and Paulello use another figure and and take care not to strain the wire beyond 70% of this.  This allows a safety margin needed to take into account friction points, weakening through work (say at the eye) etc.  From what I have read, the elastic limit of patented wire is almost coterminous with the breaking strain and there is no separate "yield point" below the breaking strain as there is with some other materials.  In other words once plastic deformation begins the string is going to break, whereas with some other materials the wire would stretch (irreversibly) without breaking over a range of tensions between the yield point and the breaking strain.  We are not concerned with such materials.</div> <div><br></div> <div>The figures I use are as below, with the tension in pounds.  70% of this figure is what I do not exceed in designing bass strings -- so 283 lbs would be the maximum tension I'd have for a covered string with a No. 21 core.</div> <div><br></div> <div>12       0.725     174<br> 12.5     0.750     185<br> 13       0.775     196<br> 13.5     0.800     207<br> 14       0.825     218<br> 14.5     0.850     229<br> 15       0.875     240<br> 15.5     0.900     251<br> 16       0.925     264<br> 16.5     0.950     276<br> 17       0.975     288<br> 17.5     1.000     300<br> 18       1.025     314<br> 18.5     1.050     326<br> 19       1.075     339<br> 19.5     1.100     339<br> 20       1.125     371<br> 20.5     1.150     387<br> 21       1.175     405<br> 21.5     1.200     421<br> 22       1.225     439<br> 22.5     1.250     455<br> 23       1.300     479<br> 23.5     1.350     504<br> 24       1.400     532<br> 24.5     1.450     570<br> 25       1.500     609<br> 25.5     1.550     660<br> 26       1.600     726</div> <div><br></div> <div>JD</div> <x-sigsep><pre>-- </pre></x-sigsep> <div >____________________________________________________________________<span ></span>__<br>   Delacour Pianos  *  Silo  *  Deverel Farm  *  Milborne St. Andrew</div> <div >           <span ></span>          Dorset DT11 0HX  *  England<br>            <span 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