Here are some of my personal opinions (standard disclaimer applies )Grkite wrote: ↑Sun Jan 14, 2018 2:19 pmThe one that I am now finishing has two strips on top with glass and carbon with glass under.
She is quite thin in the middle and really I have to add probable more heavy glass. The two carbo strips on the top with glass ...makine her flexy and strong.
For sure the best would be to able to cut the carbon sheet in shapes and put carbon where you really want to...but this is difficult to ptimize and actually to cut the carbon in stange shapes is very difficult...
With all yous discussion , I still believe carbon glass bottom and glass and carbon stiprs top will be the next one....What I would like to add in your discussion is you always have to consider the size/shape of the board..the weight of the fabrics...and the rider. Offcourse you know from FE analysis where are the areas to consider....
Finnally a question relevant to lamination ... I come across that the materials used in bottom should be the same in top....is this true? Why? Is this really a fundamental rule of lamination?.
Is there a reason due to epoxy behaviour?
Mixing glass and carbon fibres is fine, but if the carbon and glass runs in the same direction the carbon will do all the work, so the glass becomes redundant.
So when I do a cosmetic carbon finish, I prefer to do the glass at 0/90 and the carbon at -45/+45.
The easiest way to have stiffer sections (i.e. the middle of the board) is to make the core thicker, as opposed to messing with different layers of reinforcement. Each time you terminate a piece of reinforcement it introduces a localised stress riser. I prefer to run a single piece of fabric across the entire board.
There is no fundamental rule to having a mirrored layup when you do a sandwich construction, but it is a good idea.
Both the top and the bottom of the sandwich work together all the time. The tensile forces on one side of the sandwich must always be counteracted by compressive forces on the other side.
And of course the core must be able to provide support for shear and buckling.
For example if the top layer fails early under compressive loading, then it makes no difference how strong the bottom layer is, the board will break.
Another good reason for mirrored layup is that the kiteboard experiences a wide range of dynamic loads. From jumping to edging, landing on one tip, used upside down (darkslides)..
Last thing.. carbon is about twice as strong as glass, but three times as stiff. Here' a handy little chart.