The Carbon Graphite Story

Stringers Assistant, Nov '98 : USRSA

What's REALLY important in what makes a good racquet a great racquet (aside from design)...
NO, not titanium but GRAPHITE!

We've heard of graphite in racquets since the 80's but I never really knew there were so many different types of graphite (each with it's own unique characteristics)...basically, I only knew of a few like regular (?), high modulus, and Kevlar graphite. Don't even know if Kevlar IS graphite??? and what does High Modulus mean??? Apparently there's low, intermediate, high and ultra high modulus graphite...and with Wilson coming out with HYPER modulus graphite next year...it's already on their webpage but...what's HYPER GRAPHITE (aka Hyper Carbon)???

Well, an article in the Nov 1998 issue of the Stringer's Assistant (USRSA) goes into a nice description...modulus is just a synonym for stiffness...but there are different "types" of stiffness.

In either case, if your material stretches or bends alot, it is described as having a low modulus and if it bends/stretches very little, that's a high modulus...so now I know what high modulus graphite is...a graphite that bends very little relative to the regular stuff. Interesting that this being a market-driven feature of racquets...the graphite wars are between Wilson and Prince (aka Ektelon). More interesting stuff is that whoever has the highest modulus wins...this year Wilson came out with Hyper Carbon which blows every other type of graphite out of the water with "a modulus of 63.3 million pounds per square inch and a strength of 612,000 lbs".

Also interesting is that there is an entire quadrant range of graphite products from low to high strength (Y axis) and from low to high stiffness (X axis)...so you have some graphite that is not too strong and not too stiff, strong but not stiff and stiff but not strong...the tradeoff being as the stiffness increases, strength decreases.

Hyper Carbon is valuable in the respect that it is near the mean of this range and close to the second quadrant (stiff AND strong) being a little more stiffer than strong...some graphites are stiffer but are not as strong, and the others are stronger but not as stiff. But the most interesting thing is that most top-end racquets are a combination of some of these 25 or so different graphites...in other words, you won't see a racquet made up of ONLY high modulus graphite (ie Hyper Carbon) because it gives up some strength for it's stiffness, increased stiffness also means more brittle (aka breakage) and their more expensive (would you buy a $1000 racquet that broke easily).

So do you just add your 20% Hyper Carbon and put the racquet on the store shelf? NAAAAHHH...that's where design comes in. When putting this high modulus graphite stuff into a racquet, the designers must incorporate the right type of graphite (based on the desired strength:stiffness ratio) in a way to maximize it's properties.

Basically, you have a racquet which (usually :) hits a ball...you must determine the various parts of the racquet and what types of stresses are thereby imposed and coordinate the right graphite type accordingly (huh?). Interesting but what makes a graphite stiff OR strong is the angle of it's fibers. If the angle is O then the graphite fibers are aligned down the length of the material (racquet)...the material is very stiff but not too strong...all the fibers are aligned down the length. If the angle is 90 degree, you've got something very strong but not too stiff as it bends alot...and if the angle is 45 degrees you've got something in between.

But what do these "angles" mean? It's how the graphite is made...you start with acrylic sweater yarn and heat it up...and stretch it at the same time. Everything burns off except the carbon and the degree of stretching (and heating) determines what the angle of the carbon fibers will be. The more you stretch it...the closer to the 0 angle of fibers...aka the stiffest but weakest. The more you heat it, the purer the graphite but also the more brittle it becomes. The example used in the article was toasting bread...your "starting" bread slice bends but has little strength...you toast it up and the impurities are "burned off" and it's stiffer but loses strength proportionately. So that's how graphite is made...and Hyper Carbon is equated to Hyper Toast...but this stuff doesn't become brittle for some reason which, of course, is the secret ;-)

But again, more important than the quality of the material is how much is used and how...the DESIGN. These different type of graphite (with the different angles and stuff) are made into sheets...therefore, you have sheets of different graphite fibers representing different degrees of modulus and strength. In the racquet shop, you start with a wire frame and start wrapping these graphite sheets around the wire frame...resulting in maybe 5-10 different layers of sheets...sheets with different degrees of modulus wrapped around this wire frame at different angles...even having the same modulus wrapped right next too one another (layered) at different angles...so you have same AND different angles graphite fibers layered at the same AND different angles around the wire frame...are we having fun yet ;-)

Just to throw in another wrench...there is no such thing as 100% graphite because around 40% of the material is resin (aka matrix) which serves to binds and protects the fibers...ultimatly making up a composite...thereby not pure graphite. Anyway, these different sheets of graphite (plus resin) are layered in a way to optimize there individual properties (strength and stiffness) and thus designed for a certain type of player. You might have the different graphite components layered in a certain way to enhance durability, great "feel", or stiffness.

So in conclusion...what's the most important part of racquet manufacturing? Is it the design or the materials used. Hi-tech materials like high modulus and Hyper Carbon graphite are excellent materials for making strong and stiff lightweight racquets but without a proper design, their properties may be wasted. In other words, you may not be able to design a certain racquet without these materials but used inappropriately, these hi-tech materials are worthless.

For the player...there's a simple solution...we only care about results. We just have to play with the racquets and if they feel right for us...we'll give it our thumbs up and couple hundred bucks too ;-)