Cost of materials is 30-50% more than pure bidirectional e-glass if I use the minimum layers of carbon and have double the glass layers, biggest thing is building molds...I found that weight was double or more with straight glass just because I could use way less material with carbon. I used an e-glass cloth layer between the layers of carbon which helped save cost and the carbon was so much stiffer than glass when it is separated with layers glass, glass parts were .040-.125 thick, carbon .020-.030 with a layer of glass in between the carbon. These were not overly large parts, just farings but weight adds up quickly on an aircraft. Tim
Bagging made a huge difference in weight vs just a gel coated wet layup with chopped matt or heavy glass cloth to get the same stiffness.
So ast ... jsta as a comparision - what should a FRP one weigh if built with the same craftsmanship as this CF one?
It wont be as stiff...and therefore would require more structure and thus more weight to be equivalent to a carbon/epoxy based matrix. Testing is the only way to make a legitimate comparison. Stiffness is the key with carbon, kevlar resists penetration, glass cloth is strong but lacks stiffness compared to the other 2 fibers. 100% of the load in a composite structure goes through the stiffest fiber until it fails, then the load transfers to the next stiffest fiber type. So carbon is the stiffest, then aramids like kevlar, then glass. If you layup just carbon, you are wasting material, you create a box beam like structure if you fill with glass or Kevlar. The separation of layers allows the structure to maintain sufficient stiffness with reduced costs vs. pure carbon.
Unidirectional fibers also lose about 95% of their stiffness when you get 3-4 degrees away from perpendicular to the fiber flow, that is one reason to use a multi directional cloth and layer in 90/60/45/30 degree increments or some variation, meaning don't layup everything in the same direction.
Excess resin also adds weight but doesn't add anything significant to the structure, that is why they vacuum bag, to get rid of excess resin and VOC's. Autoclaves, do more of the same as bagging.
When using Kevlar, it makes it very hard to cut the matrix, that is why i use glass. Kevlar is terrible on scissors and saws. If you throw titanium fibers into the matrix, it is even worse, you will need to cut with a water jet or laser.
