Design of Field Hockey Sticks

Abstract

In the early 2000’s, the field hockey stick faced a transition from wood towards composites. Since then, the trend is to produce stiffer sticks by applying more carbon fibre to reinforce the composite. With the use of composites, sticks became lighter and stiffer, resulting in hitting the ball harder. However, the stiffer stick reduced the handling capabilities. This raises the question how the properties of the stick are related to the performance of the player. The aim of this project is to analyse how the performance of field hockey sticks is influenced by the materialisation during the design. The first part of this research is to find the relation between the performance and the stick properties. To do so, a performance index is designed based on the technical properties of the stick. The performance is defined as the balance between hitting and handling. Properties of the stick have to fulfil the performance, for which three factors are identified: stiffness, damping ratio and the coefficient of restitution. In the performance index, stiffness and the coefficient of restitution contribute to the hitting index. The handling index is affected by the damping ratio and again the coefficient of restitution. Secondly, the materialisation of the stick is investigated. Eleven prototypes were made during the project. The prototypes were made from epoxy plastic, reinforced by carbon, flax, and glass fibres, in different configurations. Carbon fibre reinforced prototypes scores highest on the hitting index and mid range on handling, whereas glass and flax fibres show better handling capabilities but are in the mid range on the hitting index. One of the downsides of using carbon fibre in hockey sticks is that vibrations occur, which are felt uncomfortably by the user. Research is done to see how the vibrations can be mitigated. Special attention is paid to the feasibility of applying flax fibres in composite sticks. Flax has high strength and stiffness capabilities compared to weight. Besides, flax has good damping characteristics. In this project, there was no relation found between the damping and the stiffness, nor with the coefficient of restitution. Also, applying a core inside, as well as applying a rubber layer on the outside, reduces the vibrations of the stick. Applying flax in a composite stick causes multiple problems. For example, the flax fibres need treatments in order to reach sufficient strength and stiffness characteristics. Also, the properties drop dramatically after a couple of wet-dry cycles. Hence, the flax fibres must not come in contact with water, which is not a feasible requirement in the current stick production. This leads to two design proposals. Firstly, improve the performance of the currently used composite sticks by adding a foam core structure. Aimed at the longer term, a new design is proposed where a plastic layer is applied on top of the composite to protect the flax from being in contact with water. The top layer could also allow for more customisation for the user by using different materials which can, for example, enhance the damping ratio of the coefficient of restitution.