Weave or lots of layers of CSM

Leon,

I have never hear of woven fiber having a bonding problem, at least not when used properly. But due to the extreme amount of forces you are looking at, it would probably be worth hiring a structural engineer to figure out the best composite schedule. Guesses on message boards just won't do, and any knowlagable person (read engineer) has to consider the liability of having people screaming down mountains on something they worked on.

 

Hey stumble

Thanks for the reply. Well that gives me confindence to do some small tests. Unfortunaly I can't afford to hire someone for suck a small personal test.

Thanks for the help

 

There is no separation when the fiber material is the same. Never it becomes isofthalic polyesters stick with thixotropic. If you do it at some time will certainly have separation

 

Leon,

That board is a beam with a support on ends. Try laying up unidirectional fibers along the length for unidirectional strength topped off with bi ax or WR laid out at 45 degree angle to absorb the twisting.

Foam core might not be the right choice as you will be bolting the wheel assembly. Try high quality marine plywood.

 

Yer this is what the other board looks like from underneath:



So what i should do is gel the mould the apply plain weave for the first layer

http://www.cfsnet.co.uk/acatalog/Plain_Weave_Glass_Fabrics.html

then use Biaxial on the next layer

http://www.cfsnet.co.uk/acatalog/Biaxial_Fabrics.html

and if i do 5 layers which would give me 3 of plain weave and 2 of Biaxial and see how that turns out?

i only used foam core in the start as i thought it would make it stronger ( how i was wrong) i dont need to use it. Im trying to replicate this board



http://www.extremekites.co.uk/mountain_boards.php?direc=trampa&content=index

they say they do different thickness for different weights and their thickest is 14ply for 70-100kg, It looks like carbon fibre but yet the cost is only £100 so i did not think it was.


Thanks again

 

HellsBells, A motorised one of those would be exciting, to say the least... and way beyond my ancient body... - - - Good on you for the adrenalin rush...

 

ITS THE BENDING, TWISTING ,AND GENERAL ABUSE OF A GUY STANDING ON A BOARD !!
CORE MATT SHOULD NEVER BE USED WHERE A PANEL IS BENDING !!!

 

Tunnels seems to be on the right track, and to add my penny's-worth? -
- The angles in the board are a weak point and high stress location...
- Make the shape curve so the wheelbase lengthens with additional down-force...
- Solidly link the structure for the wheel assembly and the "shoes"
- Let the middle part of the board do the flexing...
- Design and engineer for flex as a means to disperse the extreme loads...
- Find an engineering student who needs a research project for his post-grad-degree...

 

Yeah, Tunnels right. Spherecore or felt type materials are brittle and should only be used as bulking material in the center.

Looking at the board, the ends are angled sharply. Could be a weak point for plywood core also. Might be good to use solid laminate or maybe veneer as core material.

Give me dimensions. Length, width, height at center with curve, distance between angled ends, wheelbase. I will try some analysis.See if a core would be beneficial. The core is used for stiffness and/or to make it light.

It seems that the site is saying plain weave is 0/90 degree fabric. You should be looking for fabric that runs only in one direction, stitched together at 90 degree.

Your lay up schedule should be, Biax, Uni,Uni, Uni, Biax. always a "balanced laminate".

A 0/90 plain weave fabric can be used as a substitute for biax if you cut it in bias. That is, cut it at 45 degree angle at the width you intend to use. Just need careful handling as it stretches easily after it is cut as the weave "closes in" when stretched.

 

haha ive got a petrol powered one as well but its looking a bit sorry for its self.



ive just found that my supplier does not do uni directional but found another that does

http://www.ecfibreglasssupplies.co.uk/p-2346-320g-uni-directional-cloth-500mm-wide.aspx





really appreciate the help and so far that lay up sounds like a good place to. start. Those pics are with the dimensions as far as i can tell/

Thanks again

 

double bias uni uni uni uni double bias not biaxle

 

Leon,

I ran a quick check and it shows deflection is not a problem.

If you are going to jump on the middle for test, say 2 x your body weight, the board should be at least 4.5 mm. thick with the following layup schedule. Starting from top, Biax 600, 3x Uni @ 600 grams/m2 each (or total 1800 grams/m2 if you are using a different weight), 2x Biax 600 on the bottom.

You need 2X 600 gr. on the bottom as it is in compression. Fiber is weaker in compression plus it loses its directional strength when rotated from the zero reference.

You need to laminate with minimum resin. Try for 50% fiber content or better.

It was analyzed using polyester resin and it seems that I am getting up to 36 N/mm2 of stress. Polyester is allowed only up to 13.8 N/mm2. Epoxy has better strength.

A better analysis would be to try to break the board by jumping on the angled ends at the same time. This is representative of actual use. The ends are cantelevered design with elastic restraint and should be analyzed as such. I am not, at the moment able to do so but you should be safe with the laminate schedule I gave.

 

Thanks alot I have just got to order the weave. Thanks alot.