Hi,

Helmets are a funny one to give advice on, it's pretty important that they work! so to start I will say that you must test whatever you build and be happy that it meets or exceeds the performance required for what it is intended to do. - fortunately in you case the shell construction should be fairly easy to build to be safer than the 'standard' keeper helmet.

To keep weight within range you will want the shell to be no thicker than 2.5mm in the most part. - if you build it thicker of course it will be stronger but you will start to get pretty heavy! your main thing to consider is the fibre choice, for impact you are really looking at kevlar or diolen, the carbon will give you stiffness but can fracture more easily. You can select the outer layer for cosmetic reasons it will only amount to less than 10% of your total laminate thickness so choose whatever you like the look of! The inner layer would be best made from a heavy kevlar (like 300g) this will help stop any fractured laminate puncturing through.

So for arguments sake we shall say that we have a 200g 2/2 twill carbon on the outer skin and the 300g kevlar on the inner skin we have built up approximately 0.6mm of total thickness not leaving us with 1.4mm still available I'd look to go for a combination of carbon and kevlar here to take advantage of both the strength and stiffness maybe 2 x 450g carbon alternating with 2 x 175g kevlar would be a good place to start, so the schedule looks like this: 200g 2/2 carbon, 175g Kevlar, 450g 2/2 carbon, 175g Kevlar, 450g 2/2 carbon, 300g kevlar.

With regard to resin you are looking for something with a high mechanical performance the EL2 resin would be ideal for a high demand application such as this.

I can't stress enough the requirement for destructive testing, and a controlled manufacturing process (such as infusion), remember someone's trusting there life to your composites skills!

Paul Statham
Easy Composites / Carbon Mods - Technical

Hi guys,