Category Archives: Testing Devices

What Can Pictures Tell Us About String?

It is said that “a picture is worth a thousand words,” which may be true as long as the picture tells a story.

This story is about natural gut string, and the pictures will show what we can achieve, informationally, with our testing equipment. The two (2) strings are Babolat VS Touch 17 and Luxilon Natural Gut 125.

Both are awesome products, and we use a lot of both of them, but for different reasons, we may be able to understand by the pictures!

Our Questron software scales the images to suit the data so the graphs will not be the same size.

Babolat VS Touch 17

Our testing loads the string from 0 pounds force to 50 pounds and back to zero then up to 50 pounds three (3) times.  This is the “stress/strain” curve.  Fifty (50) pounds is arbitrary and because we are using the same methodology for all string materials it is a good number.  The closer these lines are together the better.

The farther it takes to reach 50 pounds the “higher elongation” the string is.  In this case it is about 44mm.

The important property of this string is the linearity!  That is the “straightness” of the line from beginning to end.  This indicates predictability, stability, and consistency.

This picture tells us the tensile strength and the knot strength.  In this case the knot strength is 52.3 pounds and takes a stretch to very close to 60mm before failure.

Luxilon Natural Gut 125

What is, probably, the first thing you notice about this “picture”? Could it be the squiggly lines? What could be causing this?

We believe it is the “break-in period” players associate with Luxilon gut! We have heard it from the players but have not been able to “see” it! It could be the bonding agents realigning as the load is applied.

You will notice a couple of things: the similarity of the “stress/strain” curve and the displacement to “knot strength” of the two strings. This string will feel a little less “soft” than the Babolat VS Touch 17. The linearity is quite good up to failure.

So, based on these pictures, could you make a recommendation? If so, let us hear them!

Celebrity Visitors!

The World Headquarters of Racquet Quest, LLC was happy to welcome Randy St. Pierre and Henry Hamels for a visit!

Randy is a member of the Dunlop Stringing Team and is from the UK and Henry is the principal of String MD in Florida!  Randy has been stringing racquets for quite a while and is always a source of good information…and he bought lunch!

Randy & Henry

Randy lives in a beautiful part of England so we are all invited to his house when the weather is better…is that right Randy?

Randy remembers stringing for a young player named Emma at a tournament in Nottingham when young Emma was in the 300’s  world wide!  Look at her now!  Was it Randy or something else?  I wonder!

Anyway it was great fun having these guys here and they are welcome anytime as are all of you reading this!

 

And the winner is…Head FXP 17

 

Head FXP is a string that seems to be largely overlooked and I am surprised after seeing the results of the installation and testing!

String NameCategoryGaugeUltimate Tensile Strength/LbsKnot Strength/LbsCountry of Origin
Head FXPMultifilament - Nylon17165.993.4Japan

Both the tensile strength and knot strength are exceptional and the graph shows that this string is very “elastic” which is a good thing for tennis racquet string but sometimes just not considered.

Head FXP 17

The area under the solid red lines is considered a stress-strain curve and indicates the “elasticity” of string by how close the lines fit from 0 to 50 three (3) times.  A perfectly elastic material would be one line even though it went through three (3) cycles.  What you see here is quite good and one of the reasons it is the winner!

String Evaluation Program

Racquet Quest, LLC has for years been doing the extensive evaluation of racquets and string for the benefit of our client’s customization requirements.

Now we are making this evaluation “program” available to anyone that wants to dig deeper into the workings of the string in the racquet!

This is serious stuff and requires significant resources but it is worth it!

Please contact us of you would like to take advantage of our evaluation program!

Take a look at the String Evaluation Program!

 

 

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!