Tuesday, April 15, 2008

Expert Help Wanted

I'm currently working on a problem with composite core construction. Are you an expert in this area? Can you point me in the right direction? WARNING: I'm about to seriously geek out on you here. If you don't understand what I'm talking about, this entry is not for you.

How can I maximize the strength to weight ratio in a fiberglass/Baltek Mat layup?

Here's the layup: Tap Marine Grade Epoxy with slow hardener (143), 2 mm Baltek Mat with 3.7 oz "S" glass on either side using a hand layup. Pressing it between two boards while it cures gives excellent strength but at 0.40 lb/sq ft it seems needlessly heavy and resin rich. Same layup under vacuum bagging, Mylar on one side, polyester peel ply and breather/bleeder on the other at 5" Hg drops the weight down to 0.23lb/sq ft but the stiffness suffers and there's noticeable compression (30-40%) of the core material. I'm using this as the structural support for the next solar module and I'm looking for maximum stiffness and minimum weight. Carbon fiber is a little too spendy at $40-60/yd. As a composites novice, am I really going to see performance gains if I go with carbon?


Anonymous said...

"am I really going to see performance gains if I go with carbon?"

Yes, however you could use cheaper unidirectional CF, at around $20 per metre/yard. You would not have to laminate the whole surface in order to obtain "stiffness", as you could build a "web" of thin uni strips, either single or double layers, effectivly creating a skeletal support structure.

I use the same process to stiffen kayaks when I build in thinner than usual strips of timber, when I want to use heavier exotic timbers, in order to achieve the same weight as low density timber.

CF is THE gear, and cannot be avoided in certain jobs, cost aside.

I am about to build a pair of CF chainplates for our 40ft catamaran, they will hold the mast up under considerable loads, so I would not dream of saving a few $ in this application. I guess it is all relative.

Have fun, bike looks great.


Mark said...

Thanks, Craig. I picked up some unidirectional carbon fiber yesterday and plan to make a small test panel. I've read about using unidirectional CF for tube wrapping when building a custom bike frame but didn't see how I could apply it to my flat panel until I read your suggestion.