Category Archives: Learning
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.
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!
We all know what friction is. It keeps our cars from sliding around, it keeps us from slipping and in general makes movement possible!
Friction also plays an important part in the string bed of your tennis racquet. Friction between the strings and the ball create friction which in turn creates rotation.
What are, however, some of the downsides of friction in the string bed during, and after, the stringing process?
For more detailed information and a graph showing the forces involved go to our membership site, GASP.network, but in the meantime this image will show the frictional forces at work!
This machine tension head will pull the string (blue) in the direction of the center of the racquet support structure instead of directly out the middle of the grommet.
It is obvious that this will create considerable friction and result in lower tension inside the grommet than outside the grommet.
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!
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?
Consistency is a component of almost every successful thing we do each day!
But, what does it look like? Well since this is a tennis centric post it will look like this:
What you are looking at is identical racquets, identical string, identical failure location!
If you find the very end of each string you will see how consistent this failure location is.
This string is a high elongation material so will notice that the ends of the broken strings are very far apart.
This is a good thing since it (elongation) contributes to comfort and power when hitting the ball.
This failure location indicates the player is striking the ball with consistency! That many explain the UTR of 13.3!
What else does this failure location show us?
- Most impacts are not in the center of the racquet.
- The string spacing in this area is a little more “open” which may “catch” the ball and contribute to rotation.
- There are more strings for the ball to “roll” over before leaving the racquet which may contribute to rotation.
Consistency is important in everything we do. Visualize it like the string bed of this racquet and try to hit the same spot each time you do something…anything!