Category Archives: co-polyester

In a string does color matter?

Of course color matters!  Brands have made history on color!  Prince Green, Head Orange, Babolat Blue, for racquets but what about string?

Sure, again!  Luxilon Silver, Babolat Black,  Solinco Green, Victrex Putty…what?  Which of these monofilament strings do not have any color pigment?

If you guessed the Victrex you would be correct.  But why not?  The natural color of the polymer is probably the very strongest a string can be, however, without color they would not be at all interesting or recognizable!  The natural Victrex color is typically what we use when evaluating the string because it is visually different.

Victrex does make strings with black-pigment, but this post is about the difference pigmentation can make in a string.  In a previous post some years go we determined that color had very little affect on string properties and this evaluation shows pretty much the same result in a different format.

You can see by this graph there is very little difference between the two Volkl V-Star strings.  In fact it would be safe to say the strings are identical.

We will continue to evaluate strings with pigmentation to determine if any color does exhibit an affect on the properties.

What Can String Failure Tell Us – Part Deux

In Part Un we discussed the difference between shanking (mis-hit) and friction failure.  It was obvious that the string was broken.  But what happens when it is not so obvious?

Part Deux, this part, will examine the frictional notching failure of monofilament string and how we can be prepared for it!  To further refine this discussion we will be comparing PET polyester has PEEK monofilament string.  The reason is that each material while both will notch one requires more time to reach the critical dimensional decrease that is a failure!

In almost every Racquet Quest Podcast we talk about tension v string diameter and agree that once 50% of the string diameter is notched away the string is vulnerable!  So a .050 (1.27mm) diameter string that has a tensile strength of 120 pounds at 50% notching will have 60 pounds of tensile strength remaining.

Notched v un notched string

This graph is a string that was broken during use.  The string was removed from the racquet.  The top line is the tensile strength in the area of no notching so you can see that it is pretty strong still and has stabilized due to use.  That stabilization is indicated by the very tight stress/strain grouping.

However, things go sideways when the notched area of the string is put under stress.  The string failed at a force of 63.8 pounds, or about 59% of the used tensile strength.  Not bad!

So, notching is failure-inducing but how long it takes to create the fatal notch differs with string material.  This particular set of strings had about six (6) hours of play.

In Part Trois, we will look at PEEK material under the same conditions!

 

What Can String Failure Tell Us?

Well, in the simplest terms, failure tells us it is time to have the request strung! However, there may be subtleties in string failure that can help us in our quest for tennis racquet performance.

Such as?

Is the failure shear related or tensile strength related? Was friction the major contributor to the failure? Where did the failure occur (on the racquet, not the court)? Was the failure during play or in the bag?

Shear-related failure is when the string breaks very near the racquet frame. This failure is called a mis-hit or shank! It is like cutting the string with a pair of scissors!

Shear Failure

Friction Failure

Friction failure is caused by just that, friction!  Friction is caused by the string moving on each other. That rubbing creates friction and notches the string where it will fail.

If the racquet failed during play and it is not shear-related, the tensile strength of the string was exceeded. If a string has a tensile strength of 120 pounds and the tension is 60 pounds leaving 60 pounds to be used to hit the ball. Some big hitters can generate at least that much force on a solid forehand!

The graphs show the tensile strength and relative elongation of different material.

This graph shows the tensile strength of the string to be about 115 pounds.  Given the movement of this string-on-string, the frictional notching can contribute to relatively early failure based on the hitters force.

This graph shows the tensile strength of the string to be about 155 pounds but it has to travel (stretches) further to reach that force.

So, you can see, with this information we can make better decisions when asked to suggest a string, or strings, for a client!

Which Comes First!

We all have heard the question “which comes first the chicken or the egg”?  However, my question is “Which comes first the game or the string”?

I believe they happen simultaneously.  But first a quick story.

In 2005 I was attending a Head product introduction on the island of Mallorca, Spain,  Yes, that one!

The product introduction was exciting but what I am going to tell you about now was even more meaningful.

The Director of one of the top US Tennis Training organizations, at that time, was there and we were discussing teaching techniques and what he said after being in this part of Europe was “we need to start teaching our players how to hit this way!”  Well, “this way” was the way of low-powered strings that were popular in Europe but not so much in the US, yet.

So, it began!  The players could not hit harder, like the Europeans, unless they used the same string material as the Europeans and that was very stiff and mostly PET polyester.

So, the idea was the “egg” and the string was the “chicken”, sort of!  I guess the feeling was that “if Americans are going to compete we must use the same equipment”.

Our history confirms that almost no one plays better with stiff string and durability is suffering!

Now, I believe the professional game can go on about its way but otherwise, we need to consider changing the game by returning to a combination of comfort and playability.

Our history shows us that the “high performance” life span of many polyester strings is about 2-3 hours, or less, maybe about 10-12 games.  We don’t believe this is quite long enough for most players.  But, how do you quantify “performance”?  It may be different things for different players.

There are many components to performance but what if it was associated with UTR data?  Racquet Quest can track UTR numbers and make some determinations based on that data.  If a UTR is stable or increasing it is a good bet that the performance of the player and equipment is OK.  However, if the UTR is slipping it is a good indication that something is not working as it should…but what?

We have found that, in some cases, it is injury or discomfort, that is causing the slippage!  Stop it!  The following data is for a 12 month period and acquired from the UTR website.  Even small positive changes are tough!  But negative changes seem to have an enormous impact more quickly than positive changes!

For example:

PlayerRacquetStringUTR1UTR2Delta
AHead Speed PEEK12.8412.86+ .02
BBabolat Pure AeroPolyester10.919.56-1.35
CHead Radical MPAPEEK4.505.61+1.11
DWilson Pro Staff 97PEEK5.07.03+2.03
EBabolat Pure AeroPEEK3.85.64+1.84
FWilson Blade 98 Polyester10.09.41-.59
GHead Radical ProNatural Gut3.75.15+1.45
This information is provided as a small sample comparison instrument and is not intended to pry anyone away from their favorite setup!  Even if it hurts!

 

 

 

 

Looking at the Differences

 

For the past fifteen (15) years or so, most string discussion centered on polyester. By now, you know our position on polyester, so we won’t go through that again right now. What we will go through right now is the difference(s) in a polyester string!

PET, polyethylene terephthalate, is the standard “material” in the better quality polyester string, so how can there be so many different versions of the same material?

Can you say “additives”? Luxilon has made it part of their brand to use acronyms for materials in each string’s description. ALU, for example, is aluminum, Timo is titanium/molybdenum, and I don’t know what 4G is.

So let’s take a look at the differences in a couple of polyester stings. Shown here are two (2) polyester strings, Luxilon ALU Power and Volkl V-Star. You can see the difference in stiffness between them, the V-Star being “softer,” but what you can’t see is the V-Star package does not say “co-polyester” but instead Co-Polymer!

Polyester? Co-Polyester? Co-Polymer?

We know “co” is two or more and “poly” is many, so how many of anything does any material have in it? We may never know and probably shouldn’t care as long as we have the presented data.

What can we see from this graph?

  • ALU Power reaches 50 lbs quicker (stiffer)
  • ALU Power exhibits good elasticity
  • V-Star is more linear (consistency)
  • V-Star has a greater tensile strength
  • V-Star is softer (takes longer to reach 50 lbs)

How would a player know this by just looking a the package? I am not sure! Adding the word “soft” or “comfort” or “feel” may persuade a player to try the string, but what if a better decision could be made before spending the time and money? 

No graph or chart will take the place of proper racquet stringing and setup, but it may help provide some needed information!