Carbon Fibre Properties

[andiY2K]

Hey, I have got to do a presentation on a material for my AS Physics, & I chose Carbon Fibre, I was wondering if anyone knows any of the properties of carbon fibre, like the Young Modulus & stuff like that!!

Cheers!

[ReubenG]

Are you talking about pure carbon fibres, or carbon fibre reinforced plastics (CFRP)?
When most people in motorsport talk about carbon fibre, they are really talking about CFRP.

Fibres on their own have a very high Young's Modulus in the direction of the fibre axis - about 250 GPa up 400 GPa for very carefully produced, small diameter fibres. Ultimate tensile strength ranges from 2200 MPa to 2800 MPa, again dependent on fibre diameter. In a direction perpendicular to the fibre axis, these properties are much, much lower.

CFRPs have extremely variable properties, depending on lay up direction, choice of polymer, volume fraction of fibres etc. Just as an exmaple, in a unidrectional layup, with a volume fraction of 60%, one can expect Young's modulus to be about 220 GPa in the fibre direction, 7 Gpa perpendicular, with a UTS around 1400 MPa in the fibre direction. The density is around 1.8-2 g/cm^3.

I think I originally got these values from "An introduction to composite materials "/ D. Hull and T.W. Clyne. - if you can get hold of it it's a good text.

[midzt]

I did the same for my AS materials courswork. After some research I found out ReubenG has said.

The properties vary so much I found it really hard to produce a good, accurate presentation as different sources put different figures. I think I got a pretty bad mark for it in the end.

[ketchup]

hi,

im currently doing my AS in physics and have chosen the same thing for my presentation. Is there any more info that could help me?

Thanx

[jagato00]

Hi... nice to see you...

Did you know the fact that Thomas Edison purposely took cotton fibers and later, bamboo, and converted them into carbon in his quest for incandescent lamp filaments? That's the birth of the carbon fiber for industrial use.

Three different precursor materials are used to produce carbon fibers.
Rayon, PAN (Polyacrylonitrile), and isotropic and liquid crystalline pitches.
Rayon and isotropic pitch precursors are used to produce low-modulus carbon fibers.
High-modulus carbon fibers are made of PAN or liquid crystalline pitch precursors.
In both cases, an orientated precursor fiber is spun, slightly oxidized to temperatures above 800 degC to produce a carbon fiber. The fiber modulus increases with heat treatment to temperatures from 1000 to 3000 degC.

Actually, there are many grades of carbon fibers whose properties are dependent on the precursor grade used, manufacturing and heat treatment process.

I've measured the mechanical properties with a sample developed by the Mitsubish Carbon several years ago. The fiber modulus was 800 GPa.
When we made CFRP with it, the tensile modulus and strength were 640 GPa and 1.4 GPa.
I usually used USN150 or URN300 carbon prepreg made by SK chemical in Korea, whose moduli were 130 GPa and 370 GPa. Their tensile strengths were 2 GPa and 1.5 GPa.
(You know... generally high-modulus fiber has lower strength... becaused of this fact, we usually apply two deveopment concepts, stiffness design and strength design... then we select proper carbon fiber grade.)
Increasing the modulus of carbon fibers induces the high price. URN300 has at least 5 times higher price than USN150.

The tensile modulus of the CFRP in the fiber direction can easily calculated by multiplying the fiber modulus with the fiber volume fraction. However, the properties in the transverse direction is dependent on the matrix matieral such as epoxy and phenol.

What I pointed out is that there are many types of carbon fibers and you should look into the mechanical properties when you buy it.

[WhiteBlue]

CAD programs simulate the local strength of components from the structur of the lay up. because carbon fiber has high tensile strength but low ductility it is often mixed with aramid fibers (Kevlar, the stuff that is also used for body amor. In order to achieve good weight ratio designers use paper or aluminium honey combs, hich means you get fibers on the upper and lower side and almost air only in the middle. this is because the border fibers farest away from the middle contribute the most to the strength.

[speedrcr]

Go to your schools library and look for ASM-21 (Composites) and Mil-17F. Both of these documents have enormous amounts of valuable information on composite processing, material properties, structural analysis techniques, allowables development, ect ect ect.

[C_F_D]

normally you calculate the properties of a composite or make a range of tests.
the yield stress e.a. is dependent on the strenght and the number of the C-Fibres (and their orientation!), of the matrix (your polymer) and the adhesion force between the matrix and the fibres.

go check sciencedirect for some papers (Cambridge university press got some good articles related to this topic too <- google book search)

[kilcoo316]

Go to your schools library and look for ASM-21 (Composites) and Mil-17F. Both of these documents have enormous amounts of valuable information on composite processing, material properties, structural analysis techniques, allowables development, ect ect ect.

+1


MIL-17 is the bible for composites.

[NDR008]

You might find interesting (and impress with your project) that some UK company, I think HexMC (I had attended the conference, if I find the info I will post it up) developed a few special forms of CFRP. Where they semi cure CFRP with certain special resins, chop it up into 'chips' and use this for special injection moulding to create a 'quasi-isotropic', and fluid-like properties. The purpose is to get closer to automated carbon fibre products.

However for some purposes, where you purely need properties of CFRP in one direction - manual specific lay-up is still better.

If I were you, I would first research composites in general, learn the basic ideas between particle / fibre composites / laminar composites
woven fibres, quasi-iso-directional fibres, etc.
fibre pull-out
energy absorption properties

Then start getting more specific
Glass Fibre Reinforced Plastic
Carbon Fibre Reinforced Plastic

Then look at more modern exotic forms of CFRP as the one I mentioned at the beginning.
And please, don't think like many 'boy racers' do - that CFRP is the best material for everything. It has its ideal uses and pointless uses.