Tuesday, 24 April 2012 17:06

Hockey Stick Materials - Materials - part 2

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In order to get the most out of the material, the volume fraction of fibres must be maximised (more fibres, less polymer). This can be done by reducing the space between the fibres while weaving (with an increase in cost) however this also means it is harder to get the polymer to flow between the fibres. If there is no polymer in some areas, the fibres will move out of alignment and the material will lose its stiffness and be prone to failure. Composites are composed of multiple layers of fibre cloth stacked onto one another in order to produce a part as a single layer of composite is not strong enough for most applications. Therefore, to avoid large areas of polymer buildup between layers, significant pressure must be applied to bring the layers as close as possible to eachother. Finally, the component must be heated to allow for the polymer to flow but not so hot as to allow for thermal degradation of the polymer. Careful engineering of molds must be undertaken to allow the polymer to flow in the right areas while avoiding any "hot" or cold spots. 

In short, the quality of your component depends on the quality of your manufacturing. For composites used in airplanes there are extremely high standards and parts can cost millions of dollars. However in the case of hockey sticks, higher costs could mean better quality manufacturing and better performance.

Composites get more complicated however. As mentionned previously, composites are an anisotropic material, the properties vary depending on the orientation of the fibres. Typically a fibre weave will have fibres running at 0o and 90o which means the best properties are located in the direction of these fibres - 0o and 90o. However if the loads aren't applied in these directions, we have a serious problem! The fibres won't be in the appropriate direction to handle the load and the part will likely fail. But there is a rather simple solution to this problem: stacking sequences. 

Since multiple layers of cloth must be stacked onto one another in order to form a part, we can vary the orientation of each layer and direct the fibres in the direction of the loads. In terms of stacking, we refer to the first fibre orientation as we know the fibre orientation will be identical in all quadrants. ie 0o = 90o = 180o = 270o, similarly, 45o = 135o = 225o = 315o. For example, if we have a part which is composed of 5 layers of carbon fibre, we could choose from the following stacking sequences depending on where we need the best properties : 0o 0o 0o 0o 0-- 0o 45o 0o 45o 0o -- 0o 20o 40o 60o 80o. Our first stacking sequence would be heavily oriented in the 0o direction, while all other directions would have minimal load bearing capabilities. The second sequence would be better suited to handle loads in different directions while maintaining higher properties in the 0o and 45o directions. The third sequence would have approximately equal properties in all directions. While the third option may seem like the best choice it is quite the contrary. It is effectively reducing your maximum properties in the directions required. One of my professors called a stacking sequence of this type when used with carbon fibre "Black aluminium" as carbon fibre stacked in this way would have essentially the same properties as aluminium but cost much much more to produce. In short, composites need to be engineered to work to the best of their ability by determining where the loads will be and how to orient your fibres to handle these loads. If this is not followed, you have essentially a part that could have been made much cheaper using aluminium.

 

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Read 11947 times Last modified on Sunday, 19 August 2012 17:42
Jean-Michel Roy

15+ Years experience as a goaltender

20+ Years experience playing hockey

Currently a goalie coach for Phil Martin's Goalie Academy.

E-mail: jm@thehockeyresource.ca

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Website: www.thehockeyresource.ca
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