Originally Posted by julianashaway
I believe Elasticity and Dynamic stiffness are the same. Elasticity is a strings ability to maintain its elongation (or stiffness) after being stressed or stretched out. For example, Nylon streches quite a bit (has a lot of elongation)(is not very stiff). However, after being stressed, it becomes much stiffer (has less elongation)(is not as stretchy). Zyex also stretches quite a bit. After being stressed it does not become as stiff as Nylon. The measure of a strings ability to maintain its stretch (elongation)(lack of stiffness) is elasticy (dynamic stiffness). This is the reason Nylon loses tension fater than Zyex. The more a string stretches and does not return, it actually gets slightly longer resulting in the loss of tension. Thus, Zyex holds tension better than both Nylon and Poly.
As for your first question, it remains to be seen how the abasion properties of Zyex compare to those of Poly in Tennis play. I would suspect that niether present a problem. However, I am reaching for a reason to explain the observations of Torres about loss of spin. Spin is much more related to the surface of the string than the elasticity. You want something to grab the ball. As you mentioned, the contrast created by Hybrid stinging is probably good for this.
Thanks a lot for your thoughts Julian, and thanks for contributing to this thread!
For a long time I had assumed that dynamic stiffness and elasticity were more or less the same. Therefore, it always puzzled me when people would say that "dead" poly would start hurting their arm. As string lose tension they lose dynamic stiffness. Less stiff strings should be easier, not harder on the arm. So a bit of a mystery. We know from some research done in Japan that strings that slide and snapback transmit less shock to the arm than strings that don't, apparently because that sliding and snapping back increases total dwell time. So that is one way to explain the arm-busting nature of "dead" copoly strings - if the strings are no longer able to snapback they may start transmitting more shock, even if they are less stiff (due to tension loss) than they were at the start. So then the question becomes, why are they failing to snap back. I thought the answer to this question was pretty simple: as strings lose tension they lose stiffness and therefore store and express less energy. So strings that have lost tension, may, because they are now less stiff, slide and stretch too far sideways and then not have enough energy stored in them to snapback. But, several posters have pointed out that copoly strings strung at very low tension (<35#) snap back just fine. So then the question becomes: what is the difference between a string freshly strung at 35# and one that was originally strung at 50# but is now at 35# due to tension loss? Previously, my hypothesis of choice was damage to the string, either notching or the type of abrasian and scuffing that you mentioned in an earlier post. Either would increase interstring friction and prevent snapback from occurring with the desired effect.
But some some posters have suggested that natural gut, being very elastic and maintaining elasticity very well, will still snap back even if it were rolled in the mud. So there is the second hypothesis, and the one held up by many people who talk about poly "going dead" - that if a string has lost elasticity it won't matter if there is very little interstring friction, that string won't have the energy to snap back, which would explain the observed difference between 35# freshly strung and 35# as a consequence of tension loss. I actually think this is a pretty simple research question. At present, both USRSA and TW University test dynamic stiffness and energy return after they have subjected a string to a tension loss protocol involving repeated impacts and a short passage of time. If dynamic stiffness and energy return were measured prior to this testing as well, I think it would then be possible to objectively compare a string freshly strung at 35# and one that got there after losing tension.
Anyway, I see Torres may have another hypothesis to advance (above). Still very intrigued by this string and I hope more players will catch onto it.