As technology continues to develop in sport, new composite materials are replacing the old traditional materials. Tennis rackets are no longer made of wood and sheep intestines but instead have been replaced with graphite and the strings are now made of nylon. This essay intends to discuss how old materials have been replaced by new composite materials, the manufacturing process and the benefits to the designer and consumer. Due to new technology, the tennis racket has changed materials. Throughout the history of tennis, rackets were made of laminated wood.
However, in the late 1960’s, Wilson produced a steel tennis racket which featured a wire wound around the frame to make string loops. In the 1980’s, the introduction of graphite tennis rackets changed the game. In today’s game, boron and Kevlar are still used to make the frame however it is usually mixed with fibreglass. Composite rackets are made out of layers of many different materials, with most being made out of boron, kelvin and fibreglass. Boron and Kevlar are good materials for the frame as they very light and very stiff.
Another advantage in using these materials is that they are very durable. The use of metals and composites materials also allows designers to make hollow frames. This means that the frame has a constant mass, which gives manufactures a further opportunity to reduce the frame weight whilst maintaining stiffness. The strings are generally made of nylon. Depending on the chemical composition, nylon strings can either be soft or firm. The most common grip materials that are used include rubber, leather or a synthetic polymer such as neoprene.
Synthetic grips usually have a textured surface with helps improve friction. The manufacturer has to consider many different properties when designing the tennis racket like weight and bending stiffness. The traditional tennis rackets, in order to be sufficiently durable and stiff, were typically around 370 to 430 grams in weight. However, in today’s game the rackets weigh about 200 grams. A racket that is heavier is harder to swing and harder to control giving less control to the tennis player.
Another vital property of a racket is the bending stiffness, which affects the collision on the ball and the racket. Flexible rackets bend far more on impact compared to a stiff racket that will not bend very much. More energy is absorbed by the flexible racket, with more of the energy going into the bending of the material. Stiff rackets are generally more powerful as less energy is lost in the bending of the racket therefore more energy can be returned to the ball through the strings. In order to maximise the bending stiffness, young’s modulus has to be found out.
As you apply tensile stress to the material, the material elongates. Stress is defined as the load per unit area and is measured in Pascal’s. The ratio between the original length and the change in length when a load is applied is called the strain. After the materials and properties are considered, the manufacturing process begins. The manufacturer starts by assembling the layers as a flat sandwich. It is then cut into strips and these strips are then wrapped around a hollow flexible tube. The tube is then wrapped all the way through a racket and is connected to a pump.
After this happens, heat is applied to the mould and air is pumped into the tube. The layers are then bound by the pressure of the air and the heat. Another option is to fill the hollow tube with polyurethane foam, which expands as the mould is heated. The next step is drilling and sealing the tennis racket. Once the rackets are released from the moulds, they are taken to an inspection area and the defected rackets are removed. The frame is then cut and holes for the strings are drilled. Once the drilling is finished, the rackets are brushed with a polymer coating many times and then sanded.
A predrilled strip is then inlaid in the groove around the head and the yoke is fitted into the base of the of the racket head. The racket is then strung, with the strings fitted length-wise first. The butt cap is inserted, then wind the double stick tape and grip tape around the handle. The rackets are then tested for stiffness, and check to see that the racket is evenly balanced. This completes the making of a modern day tennis racket which have many benefits to the designer and the consumer. In today’s game, the manufacturer designs the racket to give as many benefits to the consumer.
The rackets being a lighter weight helps the tennis players, as they have less weight to run around the court with meaning they can travel quicker to return the ball. Also, manufacturers can decide where the sweet spot is which gives more control to the player. The sweet spot is the centre of percussion, where the impact of the location of the ball where the force felt by your hand is minimum. If the racket is held upright and at rest, when the ball strikes the racket in the centre of its mass, the whole racket will recoil in the direction of the ball. However, if the ball hits either side, the racket will recoil but also rotate.
When holding the racket, this would result in the grip turning against your hand. The centre of percussion is the point on a racket at which the twist force is zero. When holding the racket, the sweet spots location depends on the weight distribution of the racket and where the handle is. When a ball hits the tennis racket, a huge amount of energy is involved in the collision. Most of this energy is used as kinetic energy which is used to return the ball, however the rest of the energy becomes vibration causing both the strings and the racket to oscillate.
Another aspect that has to be considered is the environmental issue that the manufacture causes. When manufacturing the tennis racket, the environmental issues have to be kept at a minimum. When making the plastic, the manufacturers have to making sure the dangerous fumes that come off the plastic are dealt with safely. As well, wood is a bio degradable unlike the materials that are used currently to make the frame meaning old tennis rackets have to be disposed of properly. There are some disadvantages to the quick development in sporting equipment.
As the style of tennis being played is different to when tennis first started, spectators have complained about the pace of the game, specifically the service. On a fast court, the service is nearly impossible to see by the naked eye with some travelling at 155 miles per hour. However, science is going behind changing the tennis ball so it slows down on the faster court to make the game more appealing to watch by spectators. A lot of research still goes into developing the racket further to further improve the game.
The science behind the making of a tennis racket is quite complex, with the manufacturer having to consider both the process and the physics behind the strings and the frame. Today rackets are being made with computer aided design and computer aided manufacturing (CAD). Tennis rackets today are aimed at being lighter with a bigger head area which is possible due to advanced composite materials. Another new development being made is the inclusion of smart materials mainly in the handle, which will help reduce the frame vibration.
Piezoelectric ceramics generate an electric charge when stress is applied and produce a force of displacement when as electric charge is applied. Despite this being a big step, it is important that not all the vibrations are taken away as it provides the player with feedback about their shot. To conclude, tennis rackets have come a long way since the racket was made in the 1960’s. The new composite materials have benefits to both the manufacturing and the consumer, as well as being more cost effective than the traditional materials. Tennis rackets will continue develop as research continues and new materials continue to be made.
