Isaac wrote: >This is to obtain the plastic deformation that happens with time, but >under the normal elastic limit, and at once. Plastic deformation under constant stress with time is creep. Steel doesn't creep. The likely explanations for "settling" have been discussed under the separate thread, but time dependent plastic deformation is not one of them. Any plastic deformation that occurs in a piano string after installing it and bringing it to pitch must be due to a sudden increase in stress above the existing elastic limit - i.e. resulting from a hard blow. Such plastic deformation is essentially instantaneous. The elastic limit is shifted to the new higher point. The same blow after that will not produce additional plastic deformation in that string. The only influence of time in this context is "when does the blow that pushes it over the limit occur after stringing?" A well designed scale should keep strings well below the elastic limit of the wire material being used, so even hard blows will not result in plastic deformations. >We see no interest in having yeld point as close as uts, seem more >than dangerous to us. Why dangerous? It's simply a matter of practicality to use wire with as large an elastic zone as possible, because that's the zone you want the wire to operate in for music applications. This can be done by reducing the plastic zone as much as possible while keeping the same ultimate tensile strength (UTS), or breaking stress - but it isn't easy, especially for a material like high carbon steel. >You give us values as 2200 and 2400 Mpa, what are they from ? These are the values I determined in tensile tests of Roslau wire. >I was explained that these value are looking like the values for the >Phosphored iron strings you wish to produce. No. The iron wire values are much lower than these. >The actual value for elastic limit of Roslau wire is 80%(approx) of >the breaking strain as checked by an independent laboratory once >(other tests will be made in the fall this year. Elastic limit or yield point is never a clean value, since there is always some gradual transition. I found the curve for Roslau wire doesn't take a dive till about 2200MPa, i.e about 91%UTS, but a slow transition probably begins somewhere around 2000MPa (80%). It's a question of looking at a shallow curve and deciding the point where it deviates from a line, something that doesn't have a very exact answer. However, certainly if you use Roslau wire close to 80%UTS you will have unstable strings until all the transition plastic behaviour has been bashed out of them. But this sort of situation is what I would call a poorly-designed scale. >Beside, I was amazed you have find yourself aggressed because you >fairly know who is Stephen Paulello, so in the same post you say he >use bad wire/bad scaling, with a little complement to Malcom Rose. >There was absolutely no marketing or commercial in my post, Stephen >tells that if you are able to provide the famous strings you say you >will produce, he will be the first to be happy to try them - same for >the model on piano action. Nothing personal or commercial intended in any of my comments...these are simply results of objective tensile tests on Paulello Type II wire [I haven't seen any of his other wire types] and all types of Rose wire [A,B,special B, C,CC, and D]. I found the same problem with all of these wires, namely too large plastic zone and too gradual elastic/plastic transition. This result is well known anecdotally for the worst culprit Rose C which behaves like saltwater taffy. After an initial stringing all these wires will be: (a) unstable under normal working stresses in scales of pianos for which the wire is intended; and (b) stabilized only by plastically stretching with [arguably undesirable] tonal consequences. Stephen -- Stephen Birkett Fortepianos Authentic Reproductions of 18th and 19th Century Pianos 464 Winchester Drive Waterloo, Ontario Canada N2T 1K5 tel: 519-885-2228 mailto: sbirkett[at]real.uwaterloo.ca http://real.uwaterloo.ca/~sbirkett
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