Combining different CRP/GRP cloths

[azmreece]

Hi everyone,
I'm new to snowboard building (that's probably what I'll mainly focus on) and I've been reading the forum for a couple of weeks, but this is my first time posting. Hopefully this hasn't been covered before (I couldn't find it), but please correct me if I'm wrong. I'm currently recovering from concussion, so please excuse any odd turns of phrase I might use.

Anyway, down to my first question: I was wondering if anyone had tried using different cloths in the same board for more precise control on torsional rigidity (and weight and maybe a couple of other things).
For example one layer of biaxial (+-45 degrees) fibreglass under the core and then unidirectional carbon fibre on the top. Or triaxial and biaxial GRP... or any combination you can think of...

Do you think this would work/be worth trying? Would it be better to have the higher number ply of cloth on top or underneath the core?

Hopefully this wasn't too nonsensical

Thanks,
Andrew

[powderho]

Hi everyone,
Do you think this would work? Would it be better to have the higher number ply of cloth on top or underneath the core?

It's not about the # of ply, it's about the aerial weight of the fabric and the orientation of the fibers. There's really a number of different ways of essentially ending up with the same laminate. You might have noticed a bunch of people talking about symmetrical laminates. This is very important mainly because it results in a more predictable product. That is, it should come out flatter and more shaped like the mold it was produced in. Of course lots of people use asymmetrical laminates all the time with excellent results, but it's not nearly as easy. Most time it will take some tweaking/experimenting in your cure parameters to get the results you are after. If you are just starting out, the decision is easy.........22oz triax, top and bottom (for skis at least).

[azmreece]

Thanks for the response, I think I'll definitely be keeping it simple, to begin with at least.

I realise perhaps I may not have worded my question quite as well as I could have.

It seems to be common to want the triaxial effect (with respect to orientation of fibres) - longitudinal fibres and at +-45 degrees - and having different cloths above and below the core would allow you to have this, but at the same time reduce weight to between around 2/3 and 3/4 of what you would have with 2 triaxial sheets. It would also probably be a looser flex (?), which may or may not be suitable for particular usage...

I may be completely wrong here but that makes sense to my concussion addled mind...

Andrew

[Wilsonhall]

Thanks for the response, I think I'll definitely be keeping it simple, to begin with at least.

I realise perhaps I may not have worded my question quite as well as I could have.

It seems to be common to want the triaxial effect (with respect to orientation of fibres) - longitudinal fibres and at +-45 degrees - and having different cloths above and below the core would allow you to have this, but at the same time reduce weight to between around 2/3 and 3/4 of what you would have with 2 triaxial sheets. It would also probably be a looser flex (?), which may or may not be suitable for particular usage...

I may be completely wrong here but that makes sense to my concussion addled mind...

Andrew

Oh ok I didnt know that. Thanks for clearing that up for me as well

[twizzstyle]

having different cloths above and below the core would allow you to have this, but at the same time reduce weight to between around 2/3 and 3/4 of what you would have with 2 triaxial sheets.

You don't get stiffness for free. Bending stiffness comes from two things - modulus of elasticity (E) and area moment of inertia (I). In a basic rectangular cross section like a ski or snowboard, if we ignore changes in width, the biggest variable for I is the height. I goes with the height cubed, so if you double the thickness of your core, you increase the stiffness by 8.

So keep that in mind first - next, as someone else said, with a composite you get the stiffness in the direction of the fiber, and virtually none orthogonal to the fiber (the epoxy has very little tensile stiffness).

The last bit - is heat expansion. As the composite cools, it expands/contracts depending on the materials. This is why most people stick with symmetric layups, to get the most predictable results after curing. (i.e. camber increase or decrease, or worse... twisted skis)

So yes - you can do asymmetric layups, but you need to adjust your core thickness to compensate, and consider the difference between a ski/board flexing upwards (putting the bottom in tension) or downwards (top in tension).

For your first board - forget all of this. You've got such a steep learning curve on so many other things, you need to keep it as simple as possible (same triax top and bottom, oriented symmetrically about the core). Then, you can start playing

Welcome to the forum/hobby!!!

[gottapparel]

how do you get the cloths that change colors like a rainbow