Hello,

Composites process engineer here with a few comments. I am not a designer by trade but know hybrid laminates are usually avoided.

The proposed mixing of fiberglass and carbon fiber brings nothing beneficial to the table in terms of structure. In order to use material as load bearing it has to be able to be stressed, this is the same problem as carbon fiber and wood. It is impossible to load up a material if it is bonded to a stiffer material. The modulus of elasticity of glass and wood are low compared to carbon fiber. Low modulus materials strain more when loaded or in other terms stretch and compress. When you load a column made of materials that have different degrees of elasticity the stiffer ones will pick up all of the load and the other materials are just sitting there. Example: in PTM&W Aeropoxy matrix the following properties Glass is .9 lb/cu in, with tensile modulus of 2,620,000 psi, and tensile strength of 9,828 psi ; and carbon is .65 lb/cu in with 8,170,000 psi tensile modulus, 75,640 lbs/in squared you can see contribution of glass is extra weight only.

Unless you want to use the carbon rods for the bending loads and glass for the torsion loads I would leave out the glass. In my world I would make a sandwich tube using 1 inner skin +/- 45 degrees pultruded carbon rod lengthwise at 4 to 8 points depending on the load requirements. Foam of appropriate density for the loads outer skin 2 layers of +/- 45 cloth. There are several ways to make this structure depending on what equipment is at your disposal.


Regards,

Charlie Johnson
Ogden, Utah


In a message dated 3/18/2012 2:00:46 A.M. Mountain Daylight Time, This email address is being protected from spambots. You need JavaScript enabled to view it. writes:



Yes, without the rods it makes a very strong mast. I’ve heard people say just to use CF and others who call for alternating FG and CF. Since CF is much stiffer than FG I’m not sure what the benefit is unless it is just to build bulk more cheaply. For a tail boom I think I would leave out the FG and just go with CF or CF with rods.