What is CFRP? and species of carbon fiber prepregs

Today I'm going to show you some species of carbon fiber materials.

What most people call as a carbon fiber is CFRP material that stands for " Carbon Fiber Reinforced Plastic".

So as it says on its name, CFRP is actuary plastic resin which contain carbon fibers inside. And carbon fibers increase resin properties strength and rigidity way higher.

Because it is resin, it is lighter than other well used metal material but weak at high temperature. 

Lay upping carbon fiber sheet to the mould is general way to produce CFRP parts.

The sheet is called "Prepreg" which has been pre-impregnated with epoxy resin to woven carbon fiber fabric.

The picture below is two different pieces of well seen CFRP material on automotive industries. Both prepreg has two direction that carbon fibers run across. Imagine that pulling you twilled cardigan, when you pull fibers toward direction fibers running you can easily feel its tough. But, pulling them diagonally it allow cloth to deform. 

Looking back the photo, the coarser cloth has more fibers, approx. 12000, bundled at each tow. The finer cloth has less fibers ,approx. 3000, and strength but give you much delicate design impression, looking the surface from outside.

Next prepreg is Uni-Direction , known as UD, and is actually un-woven.

All carbon fibers are run to the same direction. 

Because carbon fibers are not woven, there is no deformation. Then the fiber perform original properties such as wonderful strength and rigidity. 

In addition that, the carbon fibers have no bending point because it is not woven.

The bending point on carbon fiber is critical when the load is apply and will start to brake at that point.

So basically, UD has much higher performance than woven cloth CFRPs.

 

However, what will happen if you pull them to different direction?

The answer is ... just tore apart !

This is because all support carbon fibers to perpendicular direction is just epoxy resin.  Epoxy resin has incredibly low strength than carbon or metal materials.

This tells you that it is very important to well consider about load direction and twilling direction of the prepreg simultaneously when you design CFRP components.

 The unique prepreg above is commonly known as TeXtreme® prepreg which I remember some formula1 teams started to use this on their floor panels, especially RedBull formula1 team's RB6 in 2009.

Technically speaking, this has an eye to effect of opening carbon fiber bundles.

As you can see from the photo, the bundles of carbon fiber are opened and thinned. Thanks to this, prepreg gets thinner and close to uni-direction prepreg and has less bending point. Thus opened bundle prepreg shows better properties than other cloth materials.

 I'm afraid that it may confuse you but, this yellow sheet is also prepreg which is well know "Kevlar".

This is not carbon fiber material but because of its toughness, Kevlar is well applied in automotive and aerospace industries for some safety reasons.

Designing somethin with CFRP, Kevlar,  aluminum inserts or titanium is called "Composite design". In automotive industry, we need to use not only just carbon fiber but also such materials for ultimate performance component designs.