Composites Engineering
Basics of Carbon Fiber Composites
Carbon Fiber composites and metals are two very different types of materials. Metals are isotropic materials, meaning the strength of a metal is almost identical in all directions. Carbon Fiber composites are an anisotropic material, meaning they are much stronger in the direction the carbon fibers are oriented than they are in the other directions, in fact they’re about 5 times stronger than steel and twice as stiff in that direction.
One of the unique things about designing composite parts that’s different than a metal part is that you can specifically tailor the strength to your application by just orienting your fibers correctly. With metals you have to add extra material to stiffen the part in a particular direction. Composite designers use ply angles to specify what direction they want the fibers to be oriented. They’re also built up in layers almost like a stack of paper, these are called plies.
Alright, let’s look at designing something like a tube. Let’s say that 0° is the direction going down the length of the tube and 90° is the direction going around it. So if you want to optimize for bending down the length of the tube you would put more plies going down the length in the 0° direction. If you were more concerned with something like holding in pressure you would put more plies in the 90° direction. If your pipe is more like a drive shaft you would orient them in the +/- 45° direction to fight the torsion. In the case of a handguard you need some elements of each type of strength.