Cores

[Richard Ewing]

This may be a little late, but I know a little about honeycomb cores of different types and can find out what I don't know. With the cold weather coming, it may be time to move indoors and make decks. I just put some 5.6 oz carbon twill on a 1/4 inch ply core. I ran a deflection calculation based on some guesses for the laminate properties. I hope to be able to verify the guesses with the finished product.

Back to aramid cores. Generally, you should be able to select a core based the on shear strength required for a particular geometry and look for a weight of core that meets your requirement. There are several other things to check for, but basic shear strength is the first thing to look at. Shaping hex core with hand tools has not been easy for me in the past. The stuff doesn't stay put too well when you try to work it. I was thinking of trying endgrain balsa core since it has very good properties (high shear strength and modulus) and would be easy to work.

Anyway, I'd be happy to engage in some more discussion on this topic if people are still interested.

Rick Ewing

[John Gilmour]

Aramid Honeycomb material is great for static structural carbon fiber. Basically- its paper thin. Nomex is also available- but might require a special process to modify hte hobe to use it effectively.

The problem is having the aramid fiber endure the flexing put into a slalom deck. Luckily we use shape to control flex profiles in slalom decks as opposed to core taper. To try and cut honeycomb to make an accurate core profile is prohibitively expensive ($2000 per deck)in a snowboard project at MIT they did consider using aluminium honeycomb and crushing it to a profile...but that is another story.

Flex means the top gets shorter while the bottom tries to get longer- this results in shear. The shear forces can rip the paper.

The Aramid fiber is pretty strong though. You can expand the honeycomb and stand on it it you get on it carefully and it won't crush.

I do have a novel idea though for honeycomb materials to increase the shear strength but it would require redoing the layup of the hobe. It is a pretty brilliant idea though and if you know someone in the industry we could make some money with it.

Do you have access to anyone who constructs the hobes? A hobe is the layers of sheets that are glued upon each other and then later expanded through stretching to make honeycomb (not unlike how some party favor streamers with honey comb are made.)

If you just have finished unexpanded hobes you could try using pre-preg to drip into the hobes- and of course it is done for many things...but without good experience and a repeatable proceedure you are likely to make a few decks that might survive and a bunch that would likely delam. But if the stuff is free.....I say GO FOR IT! Make a bunch of decks and hopefully a few golden eggs will emerge from the bunch.

Measure the temperature, relative humidity, amount of catalyst (Harder) used as well as the time from mixing the epoxy till using it. Measure the cure rates and times in the bags.

Record all the info and hopefully you could do it again. My best advice to you is to have a cheap video camera around while you are doing this- point it at a thermometer, and hydrometer- and don't forget the pollen count- kidding. A video camera with time code lets you see exactly how you did it, when you did it. It tells you exactly how much stuff was used- your order of proceedure etc.

Afterwards you can edit the video footage into some sort of thesis for grad school.

GOOD Luck.

[Henry Julier]

I do have time on my hands. I'd like to , with help from slalom skateboarders on this forum, try and lay up a couple of boards... i'd buy the materials off of my team and if the decks work sell em to someone to have... I dunno.

They'll probably explode though.

Henry

[Terry Kirby]

Henry, hope you have some time on your hands. This is right up Gilmours ally. I once asked him a question about Gore Tex and he went into a rant for 12 hours straight. TK

PS you may want to ask Chaput as well.

[Henry Julier]

Gilmour!

Know anything about aramid honeycomb material? I have acces to a lot of it, along woth access too various biaxial carbon weaves and uni carbon like the bottom of roes... also i have acces to all types of fibreglass and epoxy. And an oven.

Henry