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View Full Version : What's the difference between High Modulus Graphite,graphite,and composite graphite?


Buckethead
07-11-2010, 06:16 PM
What are the pros and cons of each one of these materials?
How much do they affect how good or how bad the racket play?
Thanks for those who understand about this inquiry and would like to share some info with me.

vsbabolat
07-11-2010, 06:23 PM
What are the pros and cons of each one of these materials?
How much do they affect how good or how bad the racket play?
Thanks for those who understand about this inquiry and would like to share some info with me.

When a racquet is made of resin and graphite alone, it is called 100% graphite, even though it is at least 40% resin. If other materials are used, the frame is called a composite. To learn about Modulus read this article by Lindsay Crawford :
With all the ballyhoo about titanium lately, we have forgotten about the material that really makes a racquet what it is — graphite. Wilson’s introduction of the Hyper Carbon Sledge Hammer has brought graphite back to center stage. But all of a sudden it’s not as familiar anymore. We’ve heard of low, intermediate, high and ultra high modulus graphite, but now there’s hyper. And no sooner than you say “hyper,” and Prince follows with “extreme.” All this can make a person extremely hyper. What’s going on here? What is modulus? How do you achieve stiffness and strength?

Modulus and Strength

Modulus is nothing but a fancy word for stiffness. It’s a measure of how much a material will stretch if you hang a weight from the end of it. If it stretches a lot, it has a low modulus; a little, it has a high modulus. That’s pulling stiffness. There is also flex or bending stiffness. That’s measured by supporting both ends of a material and putting a weight in the middle, and measuring how much it bends. Again, a material that bends very little has a high flex modulus. It’s one of those confusing things where a little is a lot, and a lot is a little. The strength of a material is how much weight is needed to break the material.

So along comes Wilson with Hyper Carbon. It has a modulus of 63.3 million pounds per square inch and a strength of 612 thousand pounds. Is this “modu-less” or “modu-lot?” It sounds like it should do the job for my wimpy 60 mph serve. Manufacturers have played the “my modulus is bigger than your modulus” game for years. But they played it with kid’s gloves. There was no way to determine a winner. “My modulus is intermediate.” “Oh yeah, mine is high.” “Yeah, well mine is ultra high.” Then Wilson changed the rules: “Mine is 63.3 million!”

Big number, but what does it mean? What modulus category does that fall into? It depends on whose rules you play by. Below are Prince’s and Wilson’s classifications of modulus. Hyper Carbon is ultra high by Wilson’s definition and high by Prince’s. As much as the modulus game has always been marketing driven, this is great stuff. Notice that both companies agree on intermediate and below since nobody competes over being the most medium. Prince’s classification implies that 63.3 is not quite there, and even if it was, there’s so much further to go. Wilson’s does the opposite — Hyper Carbon is over the top and there’s nothing beyond.

No matter. When you go to the modulus store, what do you have to choose from? The chart below shows the strength and stiffness of real-life graphites from a number of suppliers. Each dot represents a graphite product. The graph is divided into four quadrants with an imaginary product at the extreme of each.

You can see that Hyper Carbon is really out there on the stiffometer. But Stiff-ite is much stiffer still. And look at Buff-ite. That’s hyper-strong. The other extremes are the low strength and stiffness Limp-ite, and the high strength and stiffness Halucin-ite. Ideally, you’d like to choose between graphites that follow the arrow up to Halucin-ite, because strength and modulus increase equally along this line. In real life, you can see that as modulus goes up, strength goes down. There are tradeoffs.

vsbabolat
07-11-2010, 06:24 PM
Tradeoffs mean it is unlikely we’ll see a 100% Hyper Carbon racquet. There are four reasons: First, as previously mentioned, as stiffness goes up, strength goes down. Other grades of graphite must be combined to get a good mix of strength and stiffness. Second, as modulus goes up, so does brittleness. The racquet becomes more susceptible to impact damage. Third, higher modulus is more expensive — there’s more energy costs, handling costs and quality control costs. We’re talking $1,000 racquets when you start getting into the real stiff stuff. Fourth, as modulus goes up, availability goes down. Wilson’s senior engineer Bill Severa put it this way, “It’s like the unicorn with certain high modulus graphites. You hear about them, but you can’t get a hold of them.” Gamma’s R&D manager Ron Carr adds, “Some carbon manufacturers have products on their list that exist only in theory. If you want to pay for it, they will make it for you.”

Making High Modulus Graphite?

Basically, it’s just high tech toast burning. You start with, get this, acrylic sweater yarn, and pull it through a series of high temperature toasters ranging from 1000-3000 degrees centigrade (which is hot, but only our international members know how hot). Depending on how long and how hot you toast, you burn off everything but carbon. The more you burn, the purer the carbon. The fibers are also pulled during heating to align the molecules in the same direction. The degree of purity and alignment add up to the magnitude of the modulus. And of course, more heat means more energy which means more cost.

That’s it, Hyper Carbon is hyper toast. Take a piece of bread. Bend it, drop it on the floor. No big deal. Now hyper-toast it. Try bending it — no can do. Drop it — splatter, it breaks into several pieces. It’s now stiff and brittle.

But lo and behold, Hyper Carbon racquets don’t break on sight. In fact, they hit the 700 million micro cell stuffing out of the new Tretorn balls. (Tretorn, please forgive the erroneous metaphor — it’s just an expression.) The secret is in the secret, of course, but reliable sources tell us that the secret of all racquets lies in the lay-up design.

Racquet Lay-Up

You can use all the Hyper Carbon you want, but if you use it incorrectly, you‘re up the creek with a Limp-ite paddle. Bill Severa expounds, “It would have been easy for us to add 20% Hyper Carbon and not have a noticeable difference. I could probably add it to a racquet with the goal of not making it any different than one without it. The goal, however, is to make it feel significantly different. We did.” Wilson’s Manager of R&D Po Jen Cheng adds, “There are an infinite number of ways to put together a racquet. The key is how to best use the material to maximize its properties.” And Prince’s Steve Davis sums it up saying, “I believe racquet construction is dependent on geometry and design. Materials help us perform what these geometries are to do. Design dominates. In that regard, the future is unlimited.”

Whether it’s Hyper Carbon or Limp-ite, the strength and stiffness derived from a material depend on the angle of its fibers to the forces caused by the impact of the ball. Sounds like mumbo-jumbo, but to paraphrase Ron Carr, Gamma’s R&D Manager, who would never really say the following without throwing in a “cosine” or two, “It’s just plywood. You build multiple layers going in different directions.”

Racquets are made of 5 to 10 layers of prepreg. Prepreg is a sheet of graphite fibers laying parallel to each other and coated in an epoxy resin. Because the fibers are parallel, the prepreg is called unidirectional graphite.

There is no such thing as a 100% graphite racquet. At least 40% of a frame’s material is resin, or matrix, as it is more commonly known. Hyper or not, graphite fiber is actually useless without the resin matrix which binds the fibers, transfers the load to the fibers, and protects them. Together, the fiber and matrix make up the composite. The strength and stiffness of the composite will fall somewhere between those of the fiber and matrix. So even if you start with Hyper Carbon, by the nature of the beast, the prepreg is semi-hyper. But that’s true of all grades of graphites, including Limp-ite which becomes semi-limp (though I don’t know if that is better or worse).

vsbabolat
07-11-2010, 06:25 PM
Fibers only have strength and stiffness in the direction of their length. It gets complicated, but suffice to say that in the diagram at right, the 0° fibers (in the direction of the racquet length) make the racquet stiff to bending. The 90° fibers are used to stiffen the hoop in the string pull-through direction. All angles in-between will increase torsional stiffness. Designers stack the layers so the strength and stiffness are optimized to match the racquet’s target player. To that end, each layer may have different modulus and strength properties to the one above or below it. Wilson, for example, mixes two other modulus fibers with its Hyper Carbon. Bill Severa summarizes saying, “Properties arise in combinations of angles. For example, two specific angles can combine to give great durability. Two others combine for great feel. And two others provide super stiffness. We are very specific as to where we use those combinations on a racquet.”

This is the age of the light-weight racquet. That means making a racquet with very little material, but ones that are very strong and stiff for their weight. Additionally, today’s high modulus graphite prepregs can be made half as thick as 10 years ago. That gives us twice as many layers for the same weight. Twice as many layers means many more angle combinations. That means greater customization and optimization of strength and stiffness. This in turn allows using less material overall. Thus our lighter weights.

Hyper Racquets

The Hyper Carbon Sledge Hammers are light indeed. The Sledge Hammer 115 is the lightest racquet we’ve ever weighed, with a strung weight of 236 grams.

But strangely enough, even though hyper modulus is about stiffness, neither racquet is the stiffest, according to the RDC. Neither the 115 (73) nor the 125 (77) match up to the Sledge Hammer 3.8 OS with Power Holes at 78 and the 3.8 MP at 79. Why aren’t the Hyper Sledges, with 2.0 ratings on Wilson’s swing index, stiffer than the 3.8s? First, the RDC measures flex differently than Wilson’s cantilever method. Second, true flex is measured by frequency analysis, not flex tests. And third, the RDC only measures bending stiffness, and much of the Hyper Carbon went toward shoring up torsional flex.

No matter what modulus graphite you start with, stiffness is equally determined by the angle of the material, the frame’s cross-sectional shape and height and what you’re trying to accomplish.

Conclusion

Modulus classifications are not good or bad in themselves. High modulus is not better than intermediate or low modulus carbon fiber. It depends on how they are used and to what end purpose. Without the design, the material’s properties may be wasted. Without the material, the design may be impossible. So what’s more important — the chicken or the egg? For the player, it’s the whole package that matters. How does it play? The level of sophistication of a player’s analysis as to which modulus racquet he prefers might best be summed up by the song lyric, “I love the way you do what you do when you do what you do to me.”

Buckethead
07-11-2010, 06:41 PM
Understood.
thanks a lot.

anirut
07-11-2010, 08:03 PM
Thanks, vs.