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Old 2005-06-01, 19:11   #1
Salad
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Default Why does multifilament break the cross first

Many stories say that instead of the main breaks first, the cross breaks when people change to use multifilament. I have the same experience of using Tecnifibre NRG2 17.

It is an interesting phenomenon. I try to give an explanation as follows:

Conventionally, main breaks because the mono-gut is sawed by the cross. In case of multifilament, the cross breaks because it is planed by the main. How comes?

Take a mono-gut of nylon for comparison, it is the most basic material of synthetic guts,. When hitting topspin or underspin, the mains move laterally (along the stringbed) against the crosses too. Look into a crossing, a crossing point of a main is brushing against a crossing segment of a cross. Though the segment, the displacement of the main is short, that’s enough to set up a one-to-many fight. This process undergoes and a notch on the main forms and in turn, a notch becomes a weak link of the string. Finally, the string breaks at the weakest link. This sawing process is witnessed by examining the saw-cuts, i.e. the notches on the mains.

Now considering a multifilament string made of many fibers of nylon. One of the advantages of multifilament is that when a fiber breaks, the breaking point is NOT a weak link of the string, the remaining fibers just share the tension of the broken fiber. As more fibers break, the string gets thinner, alike a higher gauge string is used, that implies the string is still playable.

To increase of lifetime of multifilament, fibers are protected by a coating and/or a wrap. The coating is an abrasion resistant material.

At home, you find many electrical cables which are divided into two groups, namely, single-wire and multiple-wire. Single-wire cable is rigid and used in electrical wiring, permanent installation. Multiple-wire cable is more flexible and widely used in electric appliances.

Same as multiple-wire cable, multifilament is more flexible, i.e. bends more if same force applies. It is equal to say that the flexural modulus is lower. When the mains move, humps (bends) of the crosses at crossings formed by the weaving of mains and crosses, move. A bending stress shifts along the crosses. Note that the moving mains are just undergoing an abrasion process. As the mains move cyclically, the repeated bending stresses on the crosses make the coating fatigue and break eventually. Once the protection is gone, the fibers of nylon of cross expose to the abrasion resistant coating of the main. The fibers of the cross are planed off bit by bit by the main’s coating. Finally, the fibers left are overloaded by the excessive tension and the cross string breaks.

Occasionally, the protection of main gone first, then the sawing process on the main takes over and the main breaks first.

Any opinions?
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Old 2005-06-01, 22:06   #2
Gaines Hillix
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Default Re: Why does multifilament break the cross first

In my experience, the mains are the first to break at least 9 times out of 10 no matter what kind of string type is being used. In fact, I can't think of the last time someone brought me a racquet to restring that had a broken cross instead of a main.
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Old 2005-06-02, 19:21   #3
Salad
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Default Re: Why does multifilament break the cross first

Hi Gains Hillix,

I just try give explanation to those players constantly break their multifilament cross string first.

Please find such players on forums:
http://tt.tennis-warehouse.com/forumdisplay.php?f=41
http://www.hktennisclub.com/forum/viewforum.php?f=6

The two processes -- sawing and planing compete each other, which one wins is still affected by the style of play, string, tension, string pattern and etc. Some scenarios and my explanations were posted on
http://tt.tennis-warehouse.com/forumdisplay.php?f=41
too.


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Old 2005-07-26, 22:47   #4
Jens
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Default Re: Why does multifilament break the cross first

For those who are interested I have made some photographs:


This is a Head T20+ Synthetic Gut (simple nylon string) main which shows significant notching at the intersection with the cross strings.


The same applies to the Babolat Tour Extreme which has a highly resistant multifilament core (Kevlar like material) but a relatively soft wrapping.


In contrast to the above main strings, this is a cross string (Pro's Pro Synthetic 130, simple nylon string) whose surface was significantly worn by the friction of polyester mains.


This is the Ashaway Dynamite 17 which is still in my racquet. The picture shows how the movement of the mains completely removed the wrapping of the central Zyex filaments on the cross strings. The Dynamite's surface is quite rough so there is enormous friction between the strings. The mains however seem to be fully intact, no sign of sawing.
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Old 2005-07-28, 10:14   #5
kwick
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Default Re: Why does multifilament break the cross first

Great pictures Joe.
By the wear marks on your Ashaway strings, it looks like you hit with so much force and spin that your mains are overlapping with each other
The only thing I would add to the discussion is you may find some crosses breaking first in some hybrid combinations. I mixed some RAB Texflex crosses with Kirschbaum Touch Turbo mains as an experiment for a high level player and 2 times the crosses broke after 4 outings. We gave up on that combination and went back to full TT.
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Old 2005-07-28, 18:35   #6
eagle
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Default Re: Why does multifilament break the cross first

Awesome photos Joe.

What brand/model macro lens did you use?

r,
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Old 2005-07-28, 21:51   #7
Salad
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Default Re: Why does multifilament break the cross first

Hi Joe,

Wonderful pictures. Great effort. Have you read my further elaboration document that emailed to you? Following are my thoughts about your masterpieces.


A discontinued product. From the picture, its construction is very interesting. Reasonably guess, the core is Kevlar-like material. This core has two special features: 1. the core is so thin. It reminded me that core has two folds of meaning. The 1st meaning is structurally, it is the part located at the center. The 2nd meaning is that it dominates the property the string. Think about the conflict of these two meaning if a string is made of a nylon tube, the thin inner core is air and the thick shell is nylon. What's the meaning of 'Core' in this case? 2. Not more than 20 strands are braided together and the white part (nylon?) is so much. Shall we still call it ‘multifilament’ string? I appreciate Babolat’s marketing. Joe, you revealed something astonishing me.


Pro’s Pro Synthetic 130. From http://www.arfaian.com/default.asp?ArtNr=2045 , its construction seems: A classical synthetic gut (nylon)mono-filament wrapped with highly elastic filaments (braided nylon filaments) with gold, silver and black color coating. Reference construction as nylon construction in http://www.stringforum.net/about_strings.php .
I have two observations about this worn string. 1. the edge of the broken coating is so ragged that it didn’t look like made by abrasion. 2. Conversely, the nylon wrap is pretty in shape and looks like a bit polished. I guess after the coating broke, the friction of sliding of the polyester main along the wrap is not high. I would like to know what the polyester main is used.


The new Ashaway Dynamite 17 is made of Zyex, the chemical name is PEEK (Poly Ether Ether Ketone), featuring a core of helically wound Zyex fibers, overbraided with high tenacity multifilament microfibers for superior wear (abrasive resistant).

From http://www.racquetballcentral.com/HT...s/stiffnes.htm , I found a helpful index, the stiffness k(lb/in) of the natural gut is 108; Dynamite WB 16 (zyex) is 145, NRG2 SPL 16 (multi) is 170; Head’s Synthetic Gut 16 (Nylon Core) is 207; Gamma’s DuraBlast 16 (Polyester) is 281; Ashaway’s Kevlar 16 (Kevlar) is 744. Dynamite is even softer than multifilament. Note the main's thickness is shown widened at the crossing. It is an indication of larger deformation of cross-section. As your description, I won’t wonder if the cross string breaks earlier.


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Old 2005-07-28, 22:01   #8
Salad
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Default Re: Why does multifilament break the cross first

BTW,

If anyone is interested in my more further elaboration, I am pleased to email you a copy fyi. and discussion.
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Old 2005-07-28, 23:45   #9
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Default Re: Why does multifilament break the cross first

@Salad
Thanks again for the great document, I have nothing to add, it explains the sawing and planing process very well. I did not check your mathematical formulas so I simply assume they are correct
If you would like to use some of the pictures here in your document to illustrate your thoughts with some real life proof, feel free to do so.

Concerning your comments on the Babolat Tour Extreme, I can say that the picture might be a bit misleading regarding the core, look at the following picture of the Babolat Syntronic 900 Zylon, which is just a thinner gauge version of the Tour Extreme:



I'm afraid I was wrong when I wrote that the Synthetic 130 was worn by a poly. I'm quite sure now that there was a Babolat Tour Extreme string in the mains, I should have written it down...
Here's the string's cross section (not very good because I don't have the proper equipment yet):



The Dynamite's wrapping seems to be quite resistant in a direction perpendicular to the string's axis, but just as sensitive in the direction along the string's axis. At the moment the wrapping has been totally worn off the cross strings in the sweetspot, but the string lasts and lasts. The Zyex fibers seem to be highly resistant even without the protective wrapping. However I will cut it out because it has lost its playability now.
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Old 2005-07-30, 12:08   #10
Salad
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Default Re: Why does multifilament break the cross first

Hi Joe,

Thank you for your generosity very much.

A charming Babolat Syntronic 900 Zylon picture - Blonde's hair waving in air.
See the description : "Syntronic" heißt die neue Saiten-Range des französischen Tennis-Spezialisten Babolat. Dabei umgeben acht Mittelstränge einen zentralen Strang. Die nur 1,15 mm dicke "Syntronic 900 Zylon" soll dünner und zugleich langlebiger sein als jede herkömmliche Polyester-Saite. Auch die "Syntronic 700 PA" soll besonders haltbar sein und hohe Beschleunigungswerte sowie eine gute Ballkontrolle ermöglichen. Die Polyester-Saite "Syntronic 800 PET" verspricht mit ihrer dreifachen Polyamid- und Silikon-Ummantelung komfortable Kontrolle, Haltbarkeit und Elastizität.
It seems to imply that the multifilament core is made of polyester.

As to the Synthetic 130, its cross-section picture plus the previous one you showed are already good enough to show the construction

Great!

Zyex is not easy to break and itself abrasion resistant. At present, I am also using Zyex string on my racquets. Your experience match my understanding. As same as you do, I re-string racquet once I find the playability drop beyond my acceptance.
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