CFRP (Carbon Fiber Reinforced Plastic)
A type of composite material that is made of carbon fibers (long fibers) arranged in one direction or woven together and hardened with resin. CFRP is so light and durable as to be often used as a material for aircrafts and sports equipment, e.g. fishing rods and golf clubs. It is, however, also a material which must be used with cautions. It is indispensable to determine the combination of fiber types and directions (fiber orientation), taking into consideration the shape of the structure and the way the load is applied, as its properties vary greatly depending on the direction of its fibers, The explanation here assumes CFRP of long fibers, but there are short fibers as well. As for short fibers, the directional dependence of properties is reduced because the fibers are randomly oriented.
Material before molding
3 of major materials are shown below:
| Yarn | Carbon fiber yarn. Woven into fabric or wrapped around pipes (filament winding) when used. |
|---|---|
| fabric | Carbon fiber woven into a sheet. |
| prepreg | A sheet made of carbon fibers aligned in one direction and impregnated with resin. The fabric above is sometimes impregnated with resin. |
Features of CFRP
– High strength and rigidity in the fiber direction (several times stronger than steel)
– The coefficient of linear expansion is small in the fiber direction. (-2×10-6～+2×10-6/K)
cf. iron:12×10-6/K，Aluminum:23×10-6/K
– low density (1.6～1.7g/cm3)
cf. iron:7.9g/cm3 Aluminum:2.7g/cm3
– Resin properties are dominant in the direction perpendicular to the fibers.
– Fibers have electrical conductivity
Cautions
-Both strength and stiffness are weak in the direction perpendicular to the fibers.
-Fibers must be inserted in the 45-degree direction when shear load is applied.
-Attention is needed to manufacturability (cracking and warping when molded)
– Isotropy (orienting the fibers so that the strength and stiffness are the same in all directions) does not have much weight advantage.
-Steel and aluminum alloy are reasonable in price if there is no weight restriction.
– Difficult to create complex shapes
– Evaluation of strength and stiffness is complicated (CAE is required)
Advantages
By taking advantage of the above characteristics, it is possible to achieve higher rigidity than steel by limiting the direction, while also achieving weight reduction and low thermal distortion. It is most effective when used on objects where the force applied can be specified to some extent (ex. truss members).