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carbon vs fiberglass

24K views 26 replies 14 participants last post by  flatline16 
#1 ·
We all know that carbon fiber is ultimately lighter than fiberglass, especially "dry carbon," but what I want to know is how much lighter is it in comparrison with cost?

Before I get silly replacing things with carbon I just wanted to see what kind of averages the two have in weight savings, especially over stock pieces on the mkII deuce. Basically so I dont go over board on price.
 
#27 ·
Caprandom said:
As far as structural purposes, carbon, glass, and Kevlar can have similar mechanical properties depending on the resin system but have benefits the other lack. Carbon is the strongest and stiffest but lacks impact and abrasion resistance.

Why is that? If you knew that carbon is the smallest diameter fiber of the 3 listed you would know that. Also the carbon back bone does not have elasticity.

Glass has superior strain at failure and is good for impact resistance and absorbing energy but it's not as stiff.
Why? Because of the crosslinking of Silica and H molecules

Kevlar is also good at impact resistance and energy absorption but has far better abrasion resistance than both carbon and glass and is used on the bottom of chassis for skid plates.
I don't use Kevlar personally because, I don't need it for my projects.

Even playing with plies can get you better impact resistance. An asymmetric layup (more plies on one side of core) will change perimeter shear properties. .
And why do you think they have different mechanical properties? Electron chemistry...which is lab knowledge...

I have been doing composites for about 12 years. I know how to build a strong part if I need and I also know how to build a cheap pretty looking part too.

Any monkey can say I chose this fiber for this process because of this property and Im an engineer.

A lot of skid plates are built asymmetrical and so are a lot of aero space components.



Caprandom said:
flaunting around that you know the exact chemical tracer that is used to make XYZ fiber and the chemical recipe for ABC resin means nothing....
Actually it does. If you know the strongest axis of the fiber you orient the that axis to take the brunt of the force. If the force comes in perpendicular to the strong axis this is where you strategically alternate weaves and reinforce stress area.

The resin polymer chemistry has ALOT more to do with strength than you think. If you don't choose the correct resin than will properly crosslink with the substrate then you get delamination. You might not beable to see it but the fabric layer would be floating inbetween the 2 resin layers.


Caprandom said:
You seem to have a lot of lab knowledge as far as the chemistry into making strands of composites and testing them but absolutely none when it comes to structural composite and engineering.

Source: Engineers that designed numerous monocoque race cars. I've also designed two composite monocoques for my universities FSAE team.
I understand a lot more than you think, I understand the process entirely. I do not know all engineering details and neither do you. If you not know the basic chemistry behind it then it will be hard for you to determine what materials you need for the job. People now days don't think for themselves they just do as told or monkey see monkey do.

Lets say your building a tarmac for the military or nasa for large craft or transport equipment. You could chose 2 materials, what would you use? Obviously cement would be one and you could use something else including the fibers you mentioned above. Once you figure out what your going to use how do you know the ratio in which to mix it?

Source: I have real world experience. I worked for NASA, DOD, Military contractors with up to 20 billion dollar contracts ect. I currently work for a engineering firm. FSAE, been there done that.
 
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