ALL ABOUT COMPOSITES AND HOW THEY ARE USED IN WINDSURFING

Tensile, Compression and Elongation

Tensile, Compression and Elongation

Have you ever tried to stick a plastic soda straw through the opening in the lid of a cup? Often the straw folds before it penetrates the lid. This action represents compression strength. If you take the same soda straw and try to stretch it by biting it and pulling it with your hand, you will nearly pull a filling out trying to break the soda straw. This action represents tensile strength. How much the soda straw stretches before it breaks indicates its elongation properties.

When thinking this example through, it becomes obvious that most materials are much stronger in tensile than they are in compression. A rope is another obvious example. Virtually no compressive strength (it lays in a coil) but great tensile strength (it can support considerable weight.) Fluids are just the opposite. Try to lift water and it runs through your fingers. Hit it flat with your hands and it resists. Have you ever done a belly flop from a diving board? If you have then you get the point. Fluids have very strong compressive strength and almost no detectable tensile strength. Gases are very much like fluids. The shock absorbers on your car -

- often employ fluid and gaseous properties in concert. Thus fluids and gases work well in hydraulics and solids work well in structures.In windsurfing we experience a cooperative relationship of the properties of solids, gases, and fluids. For the most part the gases (wind) and fluid (water) are a given. The solids are the variables, relative to yourself, that determine how fast you go, how high you jump, how well you jibe and how much fun you have. With the advent of composites, mylar and associated plastics, over the last decade windsurfing products have dramatically developed into high performance, finely tuned precision equipment.

A Brief History of Composites

A Brief History of Composites

Gulftech is keenly focused on the properties of the composite materials that form the masts, booms, fins, battens and boards. Currently, masts are our primary focus. To help you understand why Gulftech masts are different from other windsurfing masts you will need to be briefly familiarized with the history of composites. We will start with fiberglass.

Fiberglass was developed toward the latter period of the industrial revolution.Textile production (clothes, blankets, socks, shoe strings etc.) was greatly enhanced by automation machines developed during the Industrial Revolution. Mechanical looms, braiding machines, winding machines, sewing machines and the like allowed the textile industry to explode into a major economic force. Fiberglass, being a filament, lent itself to the form of yarn and thread. Existing textile technology easily structured fiberglass into woven cloth and assorted braided applications.

There has been little change in the form of composites ever since. In the late forties, science discovered a way to structure carbon atoms into a fiber. Initially, the process was impossibly expensive and carbon fiber remained unavailable for practical application until the late fifties and early sixties. Still, volume production of fibers was limited. In the seventies a new precursor with which to create carbon fiber was introduced and led to the more affordable form of carbon fiber that is used today.

The Unique Properties of Carbon Fiber

The Unique Properties of Carbon Fiber

Now, let's jump back to the beginning of this essay and look at the wonderful properties of carbon fiber that make it a super material superior to steel, aluminum or titanium. The most dramatic thing about carbon fiber is its tensile strength. It is simply amazing. And to top it off, it has almost no elongation!

Think of it. The shortest distance between two points is a straight line. With carbon fiber the line remains almost constant relative to the two points. This in itself is remarkable plus its compressive strength is, comparatively, much greater than fiberglass or most metals.
For the most part, carbon fiber has been treated like black fiberglass. It has been woven, braided and wound just the same as textiles. This robs carbon fiber of its greatest strength. Again, the shortest distance between two points idea

Just think, when carbon fiber is woven it is set up in a wave pattern as the yarn weaves under and over itself. This develops a spring effect. Braiding even further exaggerates this effect and winding is the least performance oriented use of carbon fiber of the three. In the eighties, unidirectional carbon fiber prepreg (fibers preimpregnated with high temperature cure epoxy resin) was developed as a product. It was used primarily in military aircraft.

The Beauty of Unidirectonial Carbon Fiber Prepreg

The Beauty of Unidirectional Carbon Fiber Prepreg

When the iron curtain fell and then the Soviet Union dissolved, the exclusive use of unidirectional carbon fiber prepreg for military applications yielded to the sporting goods market. The catch was that there was very little technology in place with which to apply unidirectional carbon fiber prepreg. It couldn't be braided, itcouldn't be woven nor wound plus it would be a sacrilege to ruin the beauty of such a form of material by treating it as a textile. Most companies stick with carbon yarn and textile technology.

At Gulftech we chose to build a better mouse trap utilizing 100% unidirectional carbon fiber prepreg.Let's look a little deeper into the advantages of unidirectional carbon fiber prepreg. Imagine looking at a stack of logs from the end. Because the logs are round there is always a little space between them. The same is true of fibers. Ideally, this space is filled with epoxy resin. If the fibers are not pressed tightly, they are "floating" in resin. This makes the structure brittle and diminishes the responsive properties of the carbon fibers. With unidirectional carbon fiber prepreg, the resin dispersement is close to perfect. To enhance the resin to fiber relationship Gulftech has created a process -

- to compact the fibers even closer together after they have been applied to form a mast. Finally, carbon fibers are very small. In the average mast there are close to 500,000 filaments running longitudinally the length of the mast. We are back to the shortest distance between two points concept again. If there were five filaments laid down the length of the masts it would be easy to get them straight' but when you consider 500,000 filaments, how does one get all of them to run in straight lines evenly distributed around the circumference of the mast and still be individually the same length and under the same tension? Though we cannot disclose the process (it is a trade secret) we figured out how to do it.

Types of Carbon Fiber

Types of Carbon Fiber

The story doesn't quite stop here. We have a few more tricks we want to let on about. One more time we go back to carbon fiber.

There are three forms of carbon fiber which are standard modulus, intermediate modulus and high modulus. Though complex in mathematical calculation, basically, modulus refers to the stiffness of the carbon fiber. Almost all carbon fiber parts are made from standard modulus material. The cost of the three forms of carbon fiber are not proportional.

If standard modulus costs $20.00 per pound, then intermediate modulus would cost about $80.00 and high modulus would cost about $500.00 per pound. In some of our booms and masts we use a high percent of intermediate modulus carbon fiber. Some of our masts are available made with 100% intermediate modulus carbon fiber.

RESINS

Resins

The next thing to consider is the epoxy resin that holds the fibers together. To enable you to more clearly understand resins, let's go back to the beginning of this essay one more time. Remember the tensile and compressive properties and the coil of rope metaphor? No fiber (except Boron fiber) has any compressive strength until it is saturated with some type of resin. Carbon fiber is as soft as baby's hair. A gentle feeling material. Think of saturating the carbon fiber with rubber.

It would have increased tensile strength but almost no compressive strength. Think of wetting it out with water! The fibers would become as limp as a wet mop. So you see, the epoxy resins that are used with carbon fiber must be designed to enable the properties of the fiber to be captured. While the carbon fiber is a longchain molecule, the epoxy molecule is a knot. Touch your hair; you are feeling a long chain set of molecules. Clasp your hands intertwining your fingers and squeeze. You are feeling the model of an epoxy molecule construction... a tight knot. In a composite such as a mast, the knotted epoxy molecules deeply cross-link with the long-

- chain molecules of the carbon fiber and induce a third property that neither material possesses independent of the other. A simple illustration can again be done with your hands. Make a fist over one of your fingers. Squeeze tightly and try to push or pull your finger. It won't budge, will it? Now, take the same finger and without flexing it push it against the palm of your hand. It folds, doesn't it? Imagine that if you squeezed your finger with your fist and the fingers of the fist actually grew into the finger that they trapped. That is how resins work. As a liquid, figuratively speaking, resins "melt" into the fibers and cure into a solid permanent structure that traps the fiber.

The Job of Resins

The Job of Resins

The prime job of any resin in any composite structure is load transfer. This simply refers to the requirement of the resin to allow transfer of energy from one fiber- to the next fiber to the next fiber and so on such that the load (energy dynamically incurred during mast flex, landings from jumps, chop hop, etc.) is distributed throughout the entirety of the composite structures.

Perhaps you can see why Gulftech is diligent in concentrating on achieving an optimum fiber-to-resin ratio.
As in fibers, there are different types of resin combinations. In the world of epoxy resins, there are many generic types of resins but the real secrete lies in the hardener that causes the resin to catalyze. You may be familiar with two part epoxies that you can buy in a hardware store. Part "A" is the resin and part "B" is the hardener or catalyst. Different part "B's" will radically affect the mechanical properties of a given part "A."

This is one aspect of the prime branches of research in the composite science field; how to develop a chemical catalyst (part "B") that will produce unique and desirable properties in generic epoxy resins. At Gulftech we work in alliance with companies that stay on the cutting edge of this technology. Our goal has been to achieve an epoxy system that will enhance the process that we have developed to arrange our carbon fiber into masts.

The Skew Factor and Line of True Arc

The Skew Factor and Line of True Arc

There is another development that Gulftech employs to make our masts even more uniquely responsive. Follow this reasoning; composites are built within a range. The narrower the variation in the range, the better the structure. As close to perfect as we can get, there is still an exact and precise line down the length of the masts where it forms its most perfect curve.

No other point on the circumference of the mast will produce a true arc. Any variation from this line of true arc will induce lateral twist at the top section of the masts. This "skew" at the top section causes the twist off properties of a sail to perform differently on one tack than the other. By locating the line of true arc, Gulftech masts induce uniform foils on either tack of the sail.

To make it easy to keep this line correctly located, we silk screen graphics onto the masts that clearly show at the base and at the boom clamp on area how to align your Gulftech masts in your sail. To keep any possible misalignment of the top and bottom sections of a two-piece Gulftech mast, the ends of the masts that join together at the ferrule are cut at 15 degree angles that allow them to be joined in perfect alignment every time.