HOW STRONG?

Theory of Sandwich Core Composites

t = thickness of core

               Single Skin t          Sandwich 2t        Sandwich 4t

Weight                 1                             1                           1
Strength               1                             6                           6
Stiffness               1                            12                         48     

Hence the stiffness can be controlled by altering the thickness of the core.

I've been asked how strong are carbon composite boards.
The quick answer is how strong do you want them for
the weight and flex you want?

e.g. At the extreme end...
A carbon board 17mm thick will flatten with a 1000 Kg
on it. ( See photo at bottom ), but it will weigh 3.8 Kg.

Most carbon boards will end up between 6 & 7 mm to give
the right degree of flex,  and will weigh 1.2 to 1.6 kilo

When riders refer to strength, they usually mean at what
load does the composite de-laminate. This is dependant
on the interlaminar bond of the Epoxy, rather than the ultimate
fail strength of the re-enforcement's, ( Carbon, Glass or Kevlar).

I use toughened Epoxy resins in a pre-preg formulation used for
construction in F1 racing car safety cage. Without spending a lot more for
special resin, (which would give maybe a 30% improvement, but at
least 50% cost increase), its about as strong as required.

When thickness stitching with kevlar or a process known as Z-pinning
is done or 3D woven fabrics that have some Z axis fibres are used,
the interlaminar properties will improve, (but reduce in plane properties),

Some glass fibre re-enforced boards use thermo plastic polymers to bond
the fibres together. This creates a homogenous matrix which resists
delamination but increases the overall weight of the board and as shown on
the graph below has a lower modulus. Thus to bear the same weight ,
the thickness or number of plies has to be greater.

Carbon suffers also under impacts, so if you have a habit of
dropping on  rocks  then the thermo-plastic/glass construction will
offer better resistance to damage.

The following are tests on various board compositions using
a 213 Kg load which represents the kerb weight on the rear of a small car.

They represent tests done on some of the first set of protos
and not necessarily give strength of more recent designs.

However the real test is in using it over a period of time.
The following is message AJ has sent me after over a year in use:

"have to tell you mate this board is holding out like nothing else.
Not a bit of the board has broken since you gave it to me at Luton,
pretty much unmarked as well, the ride this board gives is amazing,
turns on a penny and will take any landing you throw at it,
the pop and flex are still fantastic...." AJ:

   
    LB1 Carbon/Herex Core 10 mm 0.8 Kg
    light but very little flex. Will fail under
    higher loads.
   

                                
     MBS Core 1  7.5mm 1.33 Kg Glass/Plywood    LB4 Glass/Carbon 5mm 1.53 Kg
     Both supporting 213 Kg and designed for very light riders

    
     LB9 Carbon/Kevlar  5.4 mm 1.35 Kg
     Supports 213 Kg, but more to go

                 
      LB11 Fully lightened & Drilled Carbon/Kevlar 6.5 mm 1.18 Kg
     Takes 213 Kg easily & would probably go to 400 Kg    

       
    OK!                 LB4 + LB9 + LB11 Supports 1000 Kg
    or the Full Kerb Weight of the front of a small car.