Material Science Assignment: Material Properties of a Hockey Stick

Function

A hockey stick has specific functions that have to be taking into account when designing the hockey stick in order for it to effectively maximize the user’s performance. The main function of a hockey stick is to be able to hit a hard ball with maximum power and without being damaged or causing injury to the user. A hockey stick should be as light as the materials that it is composed of allow it to be, so that it can be easily carried around the field with minimal effort.

Hockey sticks use to be solely made from wood, usually Mulberry, but today’s hockey sticks are made of a number of materials such as fibreglass, Kevlar, Carbon fibre and resin as well as wood. A mixture if all these materials are used to create a hockey stick.

Figure 1

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Material and Mechanical Properties of Materials

A hockey stick should be quite rigid so as to be able to hit the ball but must also be slightly flexible in order to reduce the brittleness of the stick because the stick cannot break when a large amount of force is applied at the end of the stick so it must be able to slightly ‘cushion’ the force and also prevent a large vibration in the stick.

When the first hockey sticks were made, they were made of Mulberry wood. Mulberry wood was used because of its rigidity and natural ability to resist decay and was rated very high for outdoor applications. However wood was not rigid enough and was too brittle for the use of hockey sticks so new materials had to be used such as fibreglass (figure 1), Kevlar (figure 2), carbon fibre (figure 3) and resin.

Figure 2 www.baronecomposites.com

Fibreglass is used in hockey sticks because of its material properties. Fibre glass is very flexible so it allows the stick to bend and cushion the blow of the ball or another hockey stick. Fibreglass is also very strong, lightweight and a very durable material which allows the hockey stick to be light and not corrode away while it is being used on hard surfaces such as astro turf. In wooden sticks, fibreglass is placed over the head of the stick so as to prevent corrosion when the stick is being dragged along the ground. It is also a very cheap material so decreases the cost on the manufacturing of the hockey stick but at the same time keeping to the required standards.

Kevlar can also be used when making a hockey stick. It is a very strong material (stronger then fibreglass) so it is used to increase the strength of the stick. Kevlar is also quite flexible, which is one of the requirements for a hockey stick.

Figure 3
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Carbon fibre is another material that is used in the composition of a hockey stick. It is a very strong material so it can with stand a large amount of force. Carbon fibre is a very stiff material and is responsible for most of the power transfer from the stick to the ball. There are a couple of disadvantages to carbon fibre. Firstly it is quite an expensive material so increases the cost of manufacturing the stick and secondly it is very stiff and brittle which means the stick will snap under a large amount of force or pressure. To solve this problem, carbon fibre is combined with Kevlar to increase its strength and allow a certain amount of flexibility.

Resin is used as a reinforcing substance that strengthens the materials in the hockey stick. It helps prevent the stick from wearing away by, as mentioned above, covering the head of the stick with a combination of resin and fibreglass that protects the head. Resin is also the main binding substance that binds the materials such as Kevlar, fibreglass and carbon fibre together. It could be said that resin is the matrix phase in a composite stick and carbon fibre, fibreglass and Kevlar are the dispersed phase that strengthen the stick.

Manufacturing

There are number of ways to manufacture a hockey stick, it depends on the type of stick that is being manufactured.

Wooden sticks are made by firstly selecting the wood and drying it out to prevent it from warping and cracking (Mar 23, 2010 Frank Whittemore). The shaft of the stick is made by gluing two pieces of wood together and covered in an epoxy resin. Before the resin has dried on the stick a combination of fibreglass and carbon fibre are added to strengthen the stick and also make it slightly less flexible. The resin is used to bind the fibreglass and carbon fibre. After this has been done the shaft is put into a mould and placed in a press for about 20 minutes (Mar 23, 2010 Frank Whittemore) to harden the resin.

After the resin has dried the shaft is shaped and a small slit is cut into the shaft. A piece of wood that is going to be the head of the stick is shaped so as to have a small tab that fits into the small slit of the shaft. These two pieces of the stick are then glued together and sanded down. The stick is then moulded and curved using a press and adjusted to get the final shape. Once the final shape has been made the stick is covered in fibreglass and resin to strengthen the stick. Once the fibreglass and resin has dried the stick is coated with resin to prevent it from wearing away and final strengthening.

Figure 4

Composite sticks (figure 4) are made in a number of ways, it all depends on the type of hockey stick that is being manufactured. One way involves wood as a starting point. The wood is shaped into the preferred shape and sanded down. Layers of fibreglass, Kevlar and carbon fibre are placed around the surface of the wood. This way of manufacturing helps the producer create a stick that has the preferred characteristics. For example the manufacturer can decide on the amount of flexibility of the stick by applying the right amount of fibreglass to the stick. The stiffness of the stick can also be controlled by adding the preferred amount of carbon fibre to the stick. These layers are built up and moulded together using resin that also helps strengthen the stick. Once the stick has been moulded to the required shape a final coating of resin is used to protect the stick from wearing away and final strengthening.

Another way of composing a composite stick is to combine a number of fibres such as carbon fibre, fibreglass that are pre-soaked in resin and then placed in a mould. The combination of fibres are combined in a way to take on the desired shape and have specific strength properties as mentioned above by adding a certain amount of fibreglass to strengthen and make the stick to the required flexibility and carbon fibre to stiffen the stick to the required stiffness. Once the mould has cooled the stick is resined and lacquered to prevent it from wear.

Improvements

There aren’t many improvements that can be made on the already existing hockey sticks without breaking the rules of hockey which say that a hockey stick can contain any material as long as the material is not metal or contain metallic components (International Hockey Federation)

If this weren’t the case a hockey stick made of fibreglass, resin and aluminium (figure 5). The fibreglass can be used for the flexibility requirement of a hockey stick, the resin will help strengthen the stick when combined with the fibreglass. Aluminium is a very light yet strong material so it would withstand the force of the ball. Aluminium can also be pre-treated which prevents it from natural corrosion. The combination of aluminium and fibreglass will result in a very light stick that is flexible and very strong and rigid at the same time and not wear way. Aluminium is quite an expensive material so it would quite a bit to manufacture a stick with aluminium in it. Aluminium also takes alot of electricity to extract and produce so the effect on the environment would be quite negative.