The Materials and Technology used in the Design of Hockey Sticks
By Tom Cains
The Origins of the Hockey Stick
Hockey sticks were originally made from wood. The game of hockey we know today grew in popularity out of English public schools in the early 1800s, with ash used as the most common material to make sticks out of due to its favourable strength to weight ratio and its relative abundance.
When examining the original design of a hockey stick with its long handle and gently curving head, it does not take a huge leap of the imagination to notice that its shape is taken from an ash sapling bent in a hedgerow which has been cut along its length.
With the introduction of hockey to India in the second half of the 19th century, the material of choice for hockey sticks changed to mulberry which was better at absorbing impact without breaking.
The difficulty involved in sourcing or growing the perfect hockey stick was quickly realised and thus a two part construction method was adopted. The handle, which was tapered to a splice, was inserted into a head and bound together with string.
This new method had many advantages. The handle had to be strong and flexible so that it did not snap, whilst still being able to bend in order to produce the necessary hitting power. The head could be made from a harder piece of wood in order to constantly absorb the pressure of hitting a ball, whilst still maintaining its structural integrity.
The Indian Dribble Technique
The introduction of the Indian dribble technique forced a change in the way in which hockey sticks were designed. This new technique, which involved a player moving the ball quickly in front of themselves to either side by turning the stick over whilst running, was first used by the Indian and Pakistani teams in the 1956 Olympic Games.
The stick design used at this point was not well suited to such movements as the long curved head required an amount of precision which was often lacking in the heated frenzy of competitive gameplay. As a result of the emergence of the Indian dribble technique, the head of the stick was shortened with an increased curve angle to allow increased dribbling speed and accuracy.
The Modern Game
By the 1970s, the game had become much faster and harder hitting. Due to the emergence of artificial pitches which replaced grass surfaces, wooden sticks could not cope with the increased pressure exerted on them. Laminate heads were one of the first answers to this problem. Bonding layers of wood together with resin gave the sticks increased strength, allowing them to cope with the new game.
Wooden sticks have continued to be used in the modern game, although most are now reinforced with composite materials. Often the sticks are created with a wooden core and then fully encased in a composite material to provide performance benefits.
From Carpentry to Composites
The latest designs of hockey sticks use composite materials with a hollow core comprised of one or two hollow chambers in the centre.
This modern design not only allows sticks to be lighter than traditional wooden sticks but they can also be stiffer.
This increases the amount of power which can be imparted on the ball due to a more efficient transfer of energy along the shaft. The composites used in the manufacture of hockey sticks are comprised of fine fibres woven together in a two dimensional matrix enclosed in resin, which binds the structure into a coherent mass.
The Materials used in Composite Hockey Sticks
The most commonly used fibres are glass, carbon and aramid (Kevlar). Like the wooden laminates of the past, layers of fibres are placed on top of one another in order to build up the strength of the material and combine different aspects of their properties.
Fibreglass is the cheapest of the materials which can be used. It is made from fine strands of glass which are woven into a lattice and then set within resin. This material is strong, lightweight and surprisingly flexible. It is often applied to wooden sticks to help to increase their strength.
Image Credit: Shutterstock | EcoPrint
Carbon fibre reinforced polymers have an even greater strength to weight ratio. This material is commonly used in cutting edge automotive and aerospace applications but it has one major downfall ? its brittleness.
Aramid fibres (Kevlar), like carbon fibres, have a very high strength to weight ratio but unlike carbon, it is not as stiff and has remarkable impact resistant properties. As a result, aramid fibres are often combined with carbon fibres in order to get the best out of both materials.
These composite sticks are both strong and light in weight. Using the addition of Kevlar, they are able to absorb tremendous impacts without shattering or causing strong vibrations to travel up the shaft to the wrists of the player.
By changing the relative concentrations of these materials to each other, different ?feels? of sticks can be created. Using increased amounts of carbon fibre makes the stick stronger and the user is able to hit the ball harder. Using more Kevlar allows greater control of the ball due to increased impact absorption.
Using Nanotechnology in Hockey Sticks
A recent breakthrough in the design of hockey sticks is the introduction of carbon nanotubes into the resin which binds the woven fibres together. The lattice fibre construction provides strength in the lateral direction, relying only on the cylindrical shape of the hollow construction and the binding resin for tensile strength.
Carbon nanotubes are microscopic cylinders formed from a sheet of one atom thick carbon. The introduction of carbon nanotubes in a random orientation within the resin gives it increased strength in multiple directions and helps it to bind the fibrous layers together, thus creating a material with more uniform properties in all directions.
Vibration is a problem that anyone who has played hockey will have encountered. When you hit the ball for the first time on a cold day, you will feel jarring vibrations shooting up into your wrists and arms. The cold temperature stiffens composite hockey sticks, causing them to lose much of their flexibility and shock absorption properties.
Image Credit: Shutterstock | Nicholas Rjabow
As you play more and the stick warms up, the stiffness reduces and the stick becomes more responsive, not allowing offending vibrational waves to propagate up the shaft and into your wrist. One company claims to use piezo electric micro heating fibres to generate heat from the pressure associated with hitting the ball, effectively damping the vibrations.
A much more novel use of this technology was used by Head in its ?intelifibre? tennis racket range. The pressure from hitting a tennis ball was used to generate a small current from piezo electric fibres stored in the racket head.
This current was then passed to a silicon chip, which boosted the signal and sent it back out of phase. This attempted to drive the piezo fibres in reverse, causing them to vibrate with destructive interference, hopefully cancelling out the vibrations.
Invention and Innovation
The competitive nature of human interaction has often been a driver for invention and innovation. Sport is no exception. The optimisation of the materials used in hockey sticks has allowed the game to progress to the incredibly quick and powerful sport that it is today.
Sticks can withstand the great pressures involved with hitting and tackling, as well as having the precise feel needed to control the ball and dribble past opponents. It is difficult to envisage the next technological innovation involved in the design of hockey sticks but it is clear that it will come from cutting edge research in materials science.
References and Further Reading
- Stiffness Variation in Hockey Sticks and the Impact on Stick Performance – Graeme Nigel Carlisle, University of Birmingham
- Carbon Nanotubes and Graphene – Northwestern University
- Stick Technology – Grays Hockey
- 2014 / 2015 Sticks – Mercian Hockey
- Piezoelectric Materials and Applications – Why Study Materials?