NEW TWU (3-21-13): How Strings "Go Dead"

Discussion in 'Strings' started by TW Professor, Mar 21, 2013.

  1. pvaudio

    pvaudio Legend

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    I don't believe that it can actually. As TS said, even with perfectly lubricated strings, the strings will be able to slide perfectly, but when they aren't storing the energy anymore to snap back into position. If going dead, then yep adding some lubricant will help you get the most life out of them as possible. However once they're 6 feet under, it's time for the snips I think. :)
     
  2. fgs

    fgs Hall of Fame

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    i think we have two different situations here:
    1. the strings are not yet completely dead but started notching. hence the cof is higher, since the surface is increased. lubricant might diminish the friction and allow the strings to better slide.
    2. the strings are 6 feet under and even if there would be no notching at all, due to the loss of resiliency there would be no snap back anyway.

    therefore i think that lubricant cannot revive a "dead" stringbed but it can restore a little bit of the performance of a notched stringbed that still has some life in it left.
     
  3. maxpotapov

    maxpotapov Hall of Fame

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    Well, yeah, but they will be able to move if not snap back.
    And if they move, they would appear to be alive :)
    This will make a string bed less stiff/dead, if not more lively :)

    As for me, I would cut out this zombie poly stringbed anyway, and would not try to revive it with some magic potion.
     
  4. ricki

    ricki Professional

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    I have asked polystar and they replied me that Polystar Energy and Turbo and Strike are same material strings.

    Thing is: I have here two racquets strung with polystar energy at same tension. One is payaed for like 5 hours and one is unused.
    I have checked and the played one is DEFINITELY dead as it takes alot of force to displace mains and they snap back "slowly". The unplayed stringbed is so easy to displace and snapback is so fast. I will have to test it the force required to displace string with pull scale!
     
  5. maxpotapov

    maxpotapov Hall of Fame

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    Nono, wait, I was talking about hybrid setup. Of course full poly stringbed will lock in place after 5 hours, due to denting and notching.
    Not a problem with a smooth syn gut cross that just thins out and makes it even easier for poly mains to slide (like Gosen OGSM).

    Thanks for clarification on PolyStar materials!
     
    Last edited: Mar 24, 2013
  6. fgs

    fgs Hall of Fame

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    maxpotapov,

    how do you do that? i play hybrids but no matter if i take a syngut or a multi, the mains still notch pretty heavy.
    of course the synguts reduce diameter and the multis fray, but that does not prevent the poly mains to notch. with syngut i get about six-seven hitting hours till either the mains or the crosses break, but neither of them would have much lefe to live. with multis i usually restring the crosses once and then again either the mains or the second set of crosses breaks.
    some polys are dead by that time and i then decide not to restring crosses, but that is another issue - just very few did die within the first two hitting session (4hrs), but i had quite a few doing that within the third hitting session, meaning that i somehow wasted a fresh set of crosses.
     
  7. ricki

    ricki Professional

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    In full poly job, crosses are sawed in into mains (mains have notches) I move main string to sides so it slides, but much slower and tighter. My arm almost exploded yesterday, I had to swing hard to have speed on shot and keep it n court. Casual hits were terrible! With fresh Polystar energy you cant hit ball out - spin as alu power :)
     
  8. maxpotapov

    maxpotapov Hall of Fame

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    Hmm that's too bad. For some reason I thought PolyStar Energy would be more resilient than that. So maybe PolyStar Turbo is masking the aging effect by becoming smoother thus giving "easier to hit and softer" sensation as it wears out.
     
  9. Ennismt

    Ennismt Rookie

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    Pro line X similar to 4G?

    I read figures 2 and 3 in the article as showing tension loss being similar for Pro Line X and 4G. Am I interpreting this correctly?
     
  10. ricardo

    ricardo Semi-Pro

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    Lubricant VS slippery string savers...

    Instead of using lubricants to revive 'dead' strings, can you also use slippery string savers (Babolat elastocross) to do the same thing?

    I recently bought a used demo from TW that came strung.
    It felt stiff and dead.
    However, when I put stringsavers (about 70 pieces), it came alive.
    I get the same experience when using lubricants (mineral oil).
    However, the lubricant does not last that long. It is only good for about 3 hours.
     
  11. TW Professor

    TW Professor Administrator

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    Due to technical difficulties, I was only able to get good energy return values for 6 of the 15 strings, but it did include a couple of big tension losers: Black Widow and Big Hitter Black 7. The greatest loss in energy return over 2500-3000 120 mph serves was about 3%. That's not much.

    String is viscoelastic. That means that it is part viscous and part elastic. The elastic element behaves as you expect, returning most of the energy. The response of the viscous part depends on the loading time. If you put a weight on the end of the string and leave it for a long time, it keeps stretching or flowing. This is what we call creep and it is due to the viscous nature of the string. It has plenty of time to perform its slow-motion flowing. But when you impact a string with the test impact hammer, the typical dwell time is anywhere from 25-40 ms. And when you hit the strings with a tennis ball, the dwell time is about 5 ms. This is not enough time for the viscous behavior to do much. Instead the string behaves almost totally elastic.

    When you pull a string to tension before clamping it off, there is enough time for some creep to occur. When you clamp off, the string is then a fixed length, at which it stays until you cut the strings out. It does not creep. Instead, it undergoes stress relaxation (tension loss). This is just the other side of creep. In creep, you pull at a constant stress and the string keeps elongating. In stress relaxation, you pull to a certain length, and then stress declines.

    Both creep and stress relaxation occur due to the molecular makeup of long-chain polymers in polyesters. Even in a mono, the composition of the material is long chains of molecules. These molecules are strong and elastic along the length of the chain, but are weakly bonded with their other chain neighbors. On top of that, the chains are entwined, folded, twisted and curled. It is one big plate of spaghetti. When a stress is applied to the string, the chains can slip and slide against each other and unfold. When you tie off, the tension decreases for the same reason, the chains slip and slide back to a lower stress equilibrium.

    You can actually see some of this strange behavior in our testing. For example, sometimes near peak deflection and tension, you can see the string keep elongating while losing tension so that the string stays at a given peak tension for an extended period. Also, after the hammer leaves the strings, the tension is below the pre-impact tension, but it immediately starts to climb back. It has a memory. Every string does this a little, but especially polys. In fact, for many slow speed impacts, the tension will actually be higher after the impact than before.

    Manufacturers try to make the long chain molecules as straight as possible so that the string will have less creep/relaxation. This requires multiple heating, pulling, cooling sections of the process. But there is always going to be slipping and sliding, even if the molecules were all straight. Copolys play with all these bonds between and within chains to optimize particular properties.

    You are not taking string to yield points during impact. The string will almost always be on the straight line slope portion of a stress-strain curve. Yes, plastic deformation has occurred in the string. You can see this if you mark sections of your string before stringing and after you cut them out. The marked lengths will be longer and will remain longer. But this type of deformation is not occurring during impact.

    Our tests are probably much more vigorous than normal play, so the fact that evidence points to very little energy loss increase over a normal number of hits indicates that energy loss probably is not a very large contributor to strings going dead. Instead, I think that friction increases such that the string can no longer slide in either direction as efficiently, if at all, and thus both stores less and returns less. In this case, whether or not the string returns less energy as tension declines, it will still be less efficient in sliding and producing the benefits of sliding. Yes, whatever decrease in ER does occur will make matters worse but not significantly so.

    That is why adding lubrication to the strings may revive some of the benefits of the lateral string movement and snap back. It certainly did in TWU's lubrication experiment .
     
  12. Buford T Justice

    Buford T Justice Semi-Pro

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    Seeing this posted makes me realize that there was not a placebo effect going on with the hand lotion :). I honestly could not tell the difference between fresh Polylon and aged Polylon with hand lotion.

    So, I believe the Prof is basically telling us that the lion's share of "dead poly syndrome" is nothing more complex than string friction that has increased over the life of the string job.
     
  13. pvaudio

    pvaudio Legend

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    Thank you much for the reply, Professor. I do have a question, however, and it's regarding this picture of mine:
    [​IMG]

    This is WeissCANNON Scorpion crossed with Dunlop S-Gut. Reference tension was 47/50. Racquettune reading when strung was 45lbs, and at this point, 37. I had this same racquet strung at 36/38 a few months prior for a low tension test with a racquettune reading when fresh at 36.x. I could displace the strings then about as much as my racquets strung in the high 40s, which to me implies that I'm fighting an advanced version of Hooke's law. I have to put much more force in to displace the strings when fresh than when dead. That means then, as you wrote, the stiffness is less than when new. But what I'm actually doing is fighting the longitudinal force in the form of string tension by pulling the string laterally with my fingers. The further I pull the string to the side, the more quickly it snaps back when new, even at low tension (which makes sense if the strings are resilient like any other longitudinally tensioned string that is struck e.g. piano or bass strings.). When dead, however, the string barely moves back if at all.

    Now of course this could be tension loss, but if an entirely different reaction occurs when the strings are tensioned at low tension, then am I really just seeing a loss in tension and an increase in friction? What this seems like to me, and please do correct me if I'm wrong, is that it's something similar to fatigue: repeated stress which leads to damage even if the individual events would be tolerable. You mentioned that in a hit you would never exceed the elastic limit of a string, which is of course true. However, a repetitive or cyclical stress does lead to failure in materials more quickly (or at a lower stress level) than a single great stressor. Is it not reasonable that strokes of which an individual one is not damaging would be able to cause death when repeated over the course of hours?

    I'm very curious to hear what you think; I find this quite fascinating :)
     
    Last edited: Mar 24, 2013
  14. maxpotapov

    maxpotapov Hall of Fame

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    Sorry, I have missed your post. I was only making a point, that in full poly stringbed there is denting going on which locks mains in place. And yes, mains notch no matter what, but they at least can slide on Gosen OGSM, all the more as OGSM thins out.
    Now I'm using smooth poly only as a cross for synthetic or natural gut mains. No denting/locking problem this way.
     
  15. TimothyO

    TimothyO Hall of Fame

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    Even with a smooth poly cross and natural gut mains I still get some denting on the crosses.

    Certainly the majority of notching occurs as the stiffer poly crosses cut into the softer gut mains.

    But, the crosses still dent and may even develop a series of "ripples" as well. When freshly strung the gut slides smoothly out of position across the poly cross. With use a dent develops where the main touches the cross and the cross develops rough ripples which you can feel as you slide the main.

    And yet, during play, the mains return to their straight position in spite of the dented and rippled crosses.

    The level of denting and ripples seems to depend on the cross. With Focus Hex and CoFocus denting and rippling is minimal and I get easier access to spin with those crosses. With 4G I get a lot more denting and horrendous ripples and causal access to spin is lower but still far more than a homogenous string bed, even full poly.

    The reason I use 4G over Focus Hex or CoFocus now is for control, especially over an extended period. I feel like I get far greater precision of 4G even as the crosses age. Even with the ripples I still get tons of spin and lubricating the strings on occasion seems to restore the string bed's "flex" or feel.

    Based on TWU Professor's new research I might try an experiment with Prince Original Synthetic Gut crosses and might give BBO another try. OSG seems especially interesting as a potential cross with natural gut mains due to its interesting CoF behavior and low tension loss. Perhaps strung at 57/55 with natural gut mains it might provide sufficient control?
     
    Last edited: Mar 25, 2013
  16. corners

    corners Legend

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    Thanks. Does this mean that Big Hitter Black 7, which showed 88.5% energy return in your testing (62 pounds, fast swing), would show (88.5-3.0=)85.5% energy return after several thousand 120mph serves? Or is that a straight 3% reduction - 85.5% becomes 82.9%?

    I see. Thanks. That makes sense to me in the context of human connective tissue, which behaves elastically during nearly any sudden movement but will plastically deform when put under static stretch for an extended period.

    Thanks very much. I was holding lots of misconceptions about how strings lose tension.

    So available evidence suggests that any loss in resilience or elasticity that occurs is only a minor factor in "going dead", if a factor at all.
     
    Last edited: Mar 26, 2013
  17. maxpotapov

    maxpotapov Hall of Fame

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    I would love nothing more than nat/syn gut setup. But everyone says poly crosses are so much better "rails" for natural gut mains. I can see it by WC Mosquito Bite: red thin line just does not dent under Tough Gut pressure, still straight and smooth. Very reliable, but I still don't like an idea of keeping poly in my stringbed for 20+ hours.
    So if you find a good compromise with Prince Original, please let us know.
     
  18. corners

    corners Legend

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    Yeah, I'm with you. Gut/syngut plays really nice initially but the gut quickly starts getting stuck out of place. Even better would be if someone invented "rail gut."

    On the other hand, though, syngut seems to serve well as "rails" for copoly mains. Wonder why it doesn't seem to work that well for gut mains. I'm looking at a gut/OGSM 18 stringbed right now, and while the mains are well notched, the Gosen is glassy and smooth looking at the intersections (although running my fingernail over those sections I get a little "chatter.") For whatever reason, the mains are no longer snapping back. I should probably try lubing this bed and see what happens.
     
    Last edited: Mar 25, 2013
  19. Mongolmike

    Mongolmike Professional

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    String go ded, me kill sabertooth and restring club. End of thinking time. Hed hurts.
     
  20. TimothyO

    TimothyO Hall of Fame

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    Good insight Corners, thanks!

    Let us know how the OGSM ages. I'm very curious about that.
     
  21. corners

    corners Legend

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    I just put some lotion on the Global Gut/OGSM 18 stringbed. I'm not able to play at the moment, but just snapping the strings with my fingers, it seems that movement is much improved. I strung this about a year ago at 50/50 in a 16x20 95. This tension was probably too low, especially since Global does not hold tension like quality guts do. I think snapback would be even better if the tension were higher.

    Visual inspection shows deeply notched gut mains but as I mentioned above the OGSM crosses are smooth and glassy at the intersections. A few of the crosses have very tiny grooves cut in and when I run my finger nail over them I get "chatter," which can only be increasing interstring friction, but only a few strings are like this. There is a little bit of denting on the crosses but not as much as I've seen with some copolys.

    OGSM seems to have a much harder and smoother surface than some other synguts. I've got another racquet strung with full syngut (whatever Donnay puts in their factory-strung sticks) and the surface of those strings is noticeably gummy or rubbery. I can sink my fingernail a little bit into the surface. With OGSM I can't do that.

    I know that a couple posters, Hoodjem comes to mind, have used gut/OGSM quite a bit, but I don't recall any of them ever reporting on string movement/snapback. I think OGSM would be worth a punt as a cross with gut mains for anyone thinking about gut/syngut. However, I'm still high on gut/Ashaway Monogut ZX as possibly the ultimate cross for gut mains. If you haven't checked out the active thread on this new string you might want to take a look. More people are starting to try it and the reports are quite interesting.

    BTW, anyone interested in trying gut/nylon, check out this thread: http://tt.tennis-warehouse.com/showthread.php?t=356152&highlight=gut
     
    Last edited: Mar 26, 2013
  22. Buford T Justice

    Buford T Justice Semi-Pro

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    I am tempted to try the ZX with gut mains.....but hot dang the ZX will cost more than the gut mains!

    Of course, I am using Globat gut and found it online ultra cheap. The jury is still out on its longevity......so far the sample size is only 1.
     
  23. corners

    corners Legend

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    I found Global to be acceptable but it drops more tension than good gut.
     
    Last edited: Mar 26, 2013
  24. Buford T Justice

    Buford T Justice Semi-Pro

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    When pairing with a poly cross.....does the gut tension loss matter much? I am assuming no (as the poly loss is so much more rapid and larger in value).....but my experience with a gut / poly hybrid is very limited.
     
  25. maxpotapov

    maxpotapov Hall of Fame

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    Corners, your Global Gut / OGSM findings sound encouraging so far
    When I think of natural gut hybrid at the price of 1/2 set it is like greatest economy setup ever, providing level playability for 20+ hours. And no ill side effects from poly (after 5-8 hours), or cutting out crosses (which is a questionable practice).
    Besides, Gosen OGSM conveniently loses all inherent power the next training session, thus providing a perfect dampening for overly active or lower tensioned gut. Whatever little loss of spin potential compared to poly can probably be adjusted with tension and/or lubrication. Or more open string pattern (hello Tecnifibre 315 Ltd 16M!)
     
    Last edited: Mar 26, 2013
  26. corners

    corners Legend

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    In terms of racquet head deformation, which is a concern for me with gut/poly because I use some vintage racquets, having the gut lose more tension might actually be a good thing. But generally I think we want the gut mains to be at a higher tension. You don't want them sliding and deflecting too far sideways as then they won't have enough time to snap back and put extra spin on the ball. If the snap back isn't timely, spin is actually reduced and control suffers, big time.
     
  27. newyorkstadium

    newyorkstadium Semi-Pro

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    Do you intend to re-test peak force? I don't know if it is of any importance. I just noticed that the peak force results were inconclusive.
     
  28. Torres

    Torres Banned

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    That's interesting.

    I might try a silicone lubricant.

    Having a quick Google results in a number of people suggesting a PTFE based lubricant as well.
    eg. http://road.cc/content/review/66969-wd40-specialist-anti-friction-dry-ptfe-lubricant
    http://forums.noria.com/eve/forums/a/tpc/f/826604995/m/680106355
    http://motionsystemdesign.com/mechanical-pt/lubrication-tips-plastic-gears-0894/

    Apparently Molykote do a vast range of lubricants too. No idea which one would be most suitable though.
    http://www.dowcorning.com/content/appliance/?WT.svl=molykotehp&DCWS=Molykote

    Alternatively, need some string dipped in BAM...
    http://en.wikipedia.org/wiki/Aluminium_magnesium_boride
     
    Last edited: Mar 27, 2013
  29. corners

    corners Legend

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    I like your sudden enthusiasm for lube. The more different types people try the better. I don't know much about dry lubes, but in my head I'm seeing slow-mo video of ball/string impacts. There is always an explosion of fine dust that comes off the ball. I wonder if a dry lube would also get blasted off the strings by the shock and vibration of impact. Intuitively, I would think something viscous like a lotion would cling to the strings a little better. Maybe someone who actually knows something about this could chime in.
     
  30. ultradr

    ultradr Hall of Fame

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    Interesting data on rebound angle.

    From my experiences, this is a huge factor on people perceive as "power" rating
    of string (or how "lively" the string is in some cases).
     
  31. corners

    corners Legend

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    Yeah, definitely there's an argument to be made that string "power" is primarily a matter of rebound angle variations. If you haven't seen it, you might want to check out Cross and Lindsey's Spin and String String Patterns from about a month ago. It includes spin, rebound angle and ACOR measurements from a large number of different strings (polys and multis) in various patterns.
     
  32. TimothyO

    TimothyO Hall of Fame

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    I experimented with silicone and PTFE (Teflon).

    Silicone: meh, no big difference.

    PTFE: more spin and the stringbed felt lively. Of course, there are health concerns with PTFE so this was a one-off experiment. But the can recommended use for kitchen drawers and appliances!!! There's also a PTFE spray formulation specifically sold to professional kitchens and designated as "food safe". :shock:
     
  33. maxpotapov

    maxpotapov Hall of Fame

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    With a special PTFE spray formulation, food goes down smoothly.
     
  34. kaiser

    kaiser Semi-Pro

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    Ha ha, especially when fried first at high temperatures in a PTFE non-stick frying pan...
     
  35. ultradr

    ultradr Hall of Fame

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    Yeah, I've read the whole book by Cross and Lindsey.

    It took me whole 2 weeks to adjust to natural gut's rebound angle when
    I first tried it...
     
  36. corners

    corners Legend

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    Just so you know, the paper I linked to contains completely new information. In fact, much of the new information contradicts things that they wrote earlier in their two books.
     
  37. ChicagoJack

    ChicagoJack Hall of Fame

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    Hi All,

    Having looked at Mr. Lindsey's recent study pretty closely, I'm not finding much evidence to support the pretty widespread idea around here that Poly "death" has much to do with arm discomfort. Maybe I am mistaken, maybe I have overlooked something, but the study seems to indicate that loss of resiliency/elasticity, (the mostly widely held beliefs) are not the major factors here. What the study does indicate is string death is a combination of the following factors:

    1. Tension Drop.
    2. Increased COF.
    3. Decreasing longitudinal and perpendicular stiffness.
    4. Increased Dwell Time
    5. Increased String bed Deflection.

    Allow me to be precise, because the relationship of poly strings to arm pain is a big, fat, hot button issue. Personally, I would not recco poly to anybody currently experiencing pain. Nor am I disputing that improper technique and/or over training is often a key element if you have ouchies, so please spare me the bitter missives regarding proper/improper technique.

    What I am questioning, is the often heard concept that fresh poly is more arm safe than old poly. The board is overflowing with the idea that failure to re-string frequently, can increase the likely hood of arm discomfort. The trail of thoughts that accompany that concept, invariably has to do with poly losing resiliency, elasticity, or is due to an increased "boardy" feeling. This is inconsistent with the fact that poly loses tension quicker that just about any other material, something in the neighborhood of 20-30 lbs fair quickly. In addition in to significant tension loss, we also have increased dwell time, increased string bed deflection, and decreased longitudinal and perpendicular stiffness, all of which lessen impact shock.

    - A Multifiber nylon that starts at 55 and goes to 30 is going to be more comfy than a Poly that starts at 55 and goes to 30. I don't think anybody disputes that.

    - I also understand that how you get to the current tension matters. Seems reasonable that poly that starts at 40lbs, and goes to 30lbs might be more arm friendly or has more "life" to it, is "less dead" somehow than poly that starts at 55 and drops to 30.

    - Since tension loss increases with time, how is it exactly... that "old" poly, which probably has dropped into the 30's, if reference tension was 55, is somehow less arm safe than "fresh" poly in the 40's that started life at the same reference tension of 55?

    [..]

    Quote: "The results indicated that so-called string death is primarily due to the consequences of a decrease in perpendicular stiffness as well as the increasing of static and sliding friction between main and cross strings. Together, these account for most of the player's perceptions and complaints about strings "going dead." -- Link [1]

    Quote: " How Strings "Go Dead" — Part 1 dealt with several ways that strings, as players say, "go dead," including increased inter-string friction, decreasing longitudinal and perpendicular stiffness, increasing dwell time and deflection, and decreasing tension. All these effects have performance consequences. But there's another factor that peppers players' descriptions of string death — loss of elasticity due to an internal fatigue and breakdown of the string. This is often the explanation of players who experience string death as a loss of power. But is it true? Here we will examine the nature of elasticity, examine how it relates to power (in the player's meaning of shot speed), energy loss, and tension loss. The experiment described below shows that there is a decrease in rebound speed as string tension decreases with use, but this decrease is minimal in normal ranges of play. The experiment also shows that there is a relatively high energy return even when string tension is zero due to the stiffness of the string. " -- Link [2]

    Link [1] : How Tennis Strings "Go Dead" — Part 1, The Change in String Properties with Repeated Impacts

    Link [2] : How Tennis Strings "Go Dead" — Part 2, Do Strings Lose Elasticity with Repeated Impacts?

    [..]

    Nutshell : As Poly ages we have tension loss, increased dwell time, increased string bed deflection, and decreased longitudinal and perpendicular stiffness, all of which lessen impact shock. And this is less arm friendly? Have I overlooked something?

    Thanks!

    Jack
     
    Last edited: Jun 29, 2013
  38. maxpotapov

    maxpotapov Hall of Fame

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    All of that contributes to stringbed being less "responsive", providing slower and/or lesser energy return. Which in turn puts more strain on the arm as player has to hit or brush the ball harder to get the same pace or spin. Pain free means strain free.

    More elastic stringbed, based on natural gut mains, discourages player to force the racquet on the ball. And I think you get different results in terms of shock absorbtion/damage, when you swing racquet in a relaxed manner or you tense up. Much like playing with deflated balls could be more damaging to the arm than with fresh ones, even though those are much harder.
     
    Last edited: Jun 29, 2013
  39. ChicagoJack

    ChicagoJack Hall of Fame

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    Hi Max,

    Thanks for that reply, much appreciated. Your comments have got me to thinking, and upon re-reading the Part 1, I see something I may have missed. Perhaps the explanation is not so strictly associated with reduced power, (ie reduced mph) as you suggest, but in reduced slide and snap back, or more realistically, some combination or the two. In fact, the longer dwell times, increased deflection, can create higher deflection and the "trampoline" sensation which some players equate with uncontrollable power. Perhaps it's the reduced slide and snap back that creates a stiffer feeling stringbed. So these are opposing forces, (tension loss and increased COF) and one or the other will win out. The trampoliney feel from the tension loss, the stiff feel from the reduced slide and snap back. Anywhoo, that is my take on it as I am re-thinking, and re-reading this through again.

    [..]

    Quote: " The lower tensions and perpendicular stiffness of many polyesters leads to longer dwell times and greater deflection. This keeps the ball on the racquet for a longer arc of the stroke, potentially creating "power" problems with the ball going deeper, wider and higher than desired. The decrease in perpendicular stiffness also contributes to the sensation that the strings get "mushy" or behave like a trampoline. A loss of control is the end result. Further, the stroke itself may thus be affected to compensate for the changes in the string.

    On the other side of the coin, increasing static and/or sliding coefficients of friction will decrease the amount and efficiency of the sideways main string movement and snap back. This, in turn, decreases spin, lowers launch angle, and stiffens the stringbed parallel to the strings. This is perceived as a loss of power and spin as well as an increase in stiffness, harshness, and pain, especially if the player starts swinging even faster to compenstate.

    If only it were so easy. It seems whenever there is one causal factor acting to increase a performance variable, there is another that arises to decrease that variable. In this case, as tension and perpendicular stiffness decrease with repetitions, increasing the "power" behavior of the strings, so to do the repetitions increase the friction coefficients, making the strings feel stiffer and low-powered. And, then, in another turn, the decrease in tension should also decrease the friction between strings. So the strings are simultaneously gaining and losing in power behaviors or in stiffness and softness characteristics. It is the net effect that determines the player's perception of string performance."


    [..]

    Thanks again,

    Jack
     
    Last edited: Jun 29, 2013
  40. fgs

    fgs Hall of Fame

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    basically maxpotapov already expressed what is on my mind as well - i still keep up with my "not scientifically" theory that there are two ways i see polys dying and both basically lead to overhitting, which in turn will stress muscles and tendons, for some too much:

    1. the boardy turning polys will make you overhit. as the string loses it's elasticity you will find yourself hitting shorter. you then try to compensate and start muscling the ball in order to get more length. not only will you stress your joints more by this additional power you put in your strokes, but your hitting precision will most likely go down too and you will have more mishits respectively off-center hits.

    2. the ones that turn into "rocketlaunchers" (higher deflection = higher launch angle) will turn you to put more spin on the ball to keep it in. that means you will adapt to higher racquetheadspeed in order to still control the ball. again you put more stress on your tendons and your hitting window gets much smaller as the stick will cruise through the area of contact much faster, resulting again in a loss of striking precision.
     
  41. maxpotapov

    maxpotapov Hall of Fame

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    I was thinking of that as well. If we assume that snap back effect helps to put more rpms on the ball, then increase of friction and/or loss of elasticity means less help to the player brushing the ball.
    Amplitude of string deflection (or sliding movement) is one thing. How fast it snaps back is quite another. Natural gut mains deflect and slide furthest but snap back fast enough to add mph and rpm to the ball during 5 ms of impact.

    EDIT: About that trampoliney feel, I really doubt tension loss adds any "power". It simply takes away "control" as ball launches higher than before or at less predictable angle. And this maybe for the same reason: strings snap back much slower. Otherwise, why is there no trampoline effect with freshly strung poly at lower tensions?
     
    Last edited: Jun 30, 2013
  42. Ennismt

    Ennismt Rookie

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    My reading of the TW Prof studies is that stiffness is increased with increasing friction. Maybe I can find the reference to this in his writings...
     
  43. Ennismt

    Ennismt Rookie

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    Here it is:

    "If only it were so easy. It seems whenever there is one causal factor acting to increase a performance variable, there is another that arises to decrease that variable. In this case, as tension and perpendicular stiffness decrease with repetitions, increasing the "power" behavior of the strings, so to do the repetitions increase the friction coefficients, making the strings feel stiffer and low-powered. And, then, in another turn, the decrease in tension should also decrease the friction between strings. So the strings are simultaneously gaining and losing in power behaviors or in stiffness and softness characteristics. It is the net effect that determines the player's perception of string performance."
     

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