Reading Selection, Lesson 11

Perfect Teamwork

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The Masai of Kenya have been using composite materials—mud, dung, and straw—to make homes for thousands of years.

Wouldn't it be great to have a baseball team made entirely of the world's greatest pitchers? Well, no. This would not be a happy team. It wouldn’t matter how many strikes these superstars could throw. A team without players who are good at catching, hitting, and stealing bases would have a hard time winning. A team with a good balance of skills is more likely to make it to the World Series.

Combining skills is important for making strong materials, too. Often, a pure substance on its own does not have all of the necessary properties for a particular material. But you can make many useful materials by combining two or more substances that have different properties. The result is a mixture called a composite. A good composite exploits the best properties of each ingredient.

People have been making composites since the beginning of civilization. For ancient peoples, dried mud and even animal dung were handy for making huts. The huts were simple to make: Find dirt, add water. The mud kept out the wind and didn’t rot, but it crumbled and cracked. Ancient peoples also used straw, grass, or sticks, which were woven into durable mats, to make hut walls. But woven walls leaked.

The solution was to combine the two. In many parts of the world, people realized they could weave a house frame (usually supported by timber) out of straw, grass, or sticks and cover it with mud. The result, called “wattle-and-daub” construction, wasn’t always pretty. But it kept out the cold and did not fall apart every time the kids got a little rowdy.

People have been coming up with new composite materials ever since. Usually, a composite has two materials with opposite properties. The two materials put together as a composite can do what each ingredient alone cannot. Like ancient wattle-and-daub huts, modern composites are often made of fibers embedded in a solid that sticks the fibers together. The fibers are strong but floppy. The solid isn’t floppy, but it easily shatters or cracks. A combination of these two opposites can be unbeatable. The solid provides stiffness. The fibers keep the solid from cracking apart. (This is because a crack would have to break too many of the strong fibers running through the solid.)

Why are fiberglass and carbon fiber composites good materials for making fishing rods?

Fiberglass is one example of a modern composite. To make fiberglass, glass is melted and stretched into long threads. The glass threads are woven into cloth. The cloth is embedded in plastic goo, and the whole thing is shaped in a mold. When the goo hardens, the object has the shape of the mold, is light in weight, and is cheap to make. Fiberglass was originally developed to cover radar dishes on World War II bombers. It is now used for everything from boats to fishing rods to picnic tables.

More recently, engineers have developed new composite materials. One of these composites contains carbon fibers that are stiffer and much more heat-resistant than glass is. A given weight of carbon composite is stronger than steel. This lightweight strength makes carbon composites ideal for use in many types of objects that would normally be made of metal. The wings of jet fighter planes and helicopter blades are two examples. Composites are widely used in sports equipment and are replacing many natural materials. For example, tennis rackets, originally made from wood, now have frames made from glass, carbon, or boron fibers embedded in a plastic-like nylon.

Navy Blue Angels fly F/A-18 Hornets with composite wings.

The core of the racket is made from a plastic foam. The result is a lightweight, stiff racket that is easy to control and that returns the ball with maximum force.

Even though carbon composites are one of the latest advances in composite materials, they share something with ancient mud huts. Both combine the best parts of different materials to make something that is better than either one alone.

About 50 years ago, solid wooden rackets were used to play tennis.

Questions

1.  What is one object made from a composite material that you can find in your home?

2.  What is the function of the object?

3.  Why was that composite material chosen for that function?

Modern rackets like this one, made from several types of composites, are much stronger and lighter than wooden rackets.