I have noob question,I dont understand why are parts made from woven carbon fiber composite stiff.
I understand that carbon fibers are strong and have high Young modulus,its stiff and strong when the applied force is tensile type parallel to the direction of the fibre,basically its strong and doesnt stretch when we use it as rope and hang some weight from it,but otherwise,its very flexible yarn.
The woven twill cloth without resin is not much stiffer when it comes to holding complex 3D shape,like car mirror for example,than t shirt or woven shopping bag.Its still massively strong and stiff under tensile load in the direction of fibre,but if force is applied in any other direction,its extremly weak and soft.
Even when epoxy resin is applied,and its cured properly,I dont understand how the carbon fiber can improve strenght or stiffness over the values provided by the epoxy which have lower tensile strenght and Young modulus than carbon fiber,but is isotropic so its strong and stiff more equaly in all directions.
For example when making car mirror,there is not much tensile load,I dont understand how could carbon fiber improve it,why not just make it from epoxy resin only and skip the CF.When car goes fast it blows air on the mirror,its pressure/compressive force perpendicular to the woven carbon fiber surface,when it comes to perpendicular compressive force,as when crushing in hand carbon fiber cloth in 3D shape,its about as strong and stiff as pajamas.
I dont understand how this carbon fiber twill cloth that is soft and weak in every possible direction except when trying to stretch it becomes super stiff once resin was cured.I cant imagine reason why it would be any stiffer in ability to hold complex 3D shape than the stiffness of the epoxy resin alone,since when force is applied perpendicular to fibers,the fibers have practicly zero strenght and stiffness,so they cant contribute to the stiffness of the part.
Maybe car mirror is vague and unclear example,sphere is better.If I imagine carbon fiber composite sphere,I dont see how it will be stiffer against crushing force than cured resin alone without CF.Even if you tried to stretch it by grabbing left and right side of sphere,the carbon fiber will not begin to be loaded in tensile kind of way until the sphere collapsed into pancake disk shape.
Is there some "mechanism",some fundamental factor that I dont understand, that helps the cured resin to "translate" the high tensile stiffness of carbon fiber to other directions,so the cured part,such as mirror,sphere or car wheel are stiff and hold their shape against crushing,twisting forces?