Fibre Volume Fraction

General Composites Discussions Engineering Talk
#1

Hi all I often get asked if I can achieve a given Vf when I have to design and manufacture a carbon fibre preform. If I know the weight (gsm or actual weight) of my preform and I know the density in tex (g per 1000m) of the fibres which make up the preform then what else do I need to know in order to calculate what the Vf will be?

Bear in mind that my preform may be a 3D preform with different thicknesses throughout and different densities of fibres depending on the structure.

Hoping for some easy to understand responses! I am a jacquard weaving specialist in a composite world so I need to bring the 2 worlds together and understand them!

#2

You need the volume of the part (client should have that). Together with the Vf this determines how much volume of fiber you should put in the preform, and using the density of the fiber, and the tex, you know how much meter of roving should go in the preform.

#3

Thanks. Already that is a big help. Now when you say the volume of the part… will this be a measure of cc or weight?

#4

Measure of CC.
Weight is uhhh weight, mass.

#5

If you already know what the fiber weight fraction is, and you know the density of the fibers and cured resin, you can calculate the FVF using the following formula:

FVF = (FWF/FD) / ((FWF/FD) + (1-FWF)/RD)

where: FVF = fiber volume fraction, FD = fiber density, FWF = fiber weight fraction, RD = resin density

Fiber density for E-glass is typically 2.52-2.60 g/cc, standard modulus carbon is around 1.80 g/cc, & aramid is around 1.44 g/cc. Cured resin density is usually thickier to find but is generally in the 1.0-1.2 g/cc range for most polyesters, vinylesters, and epoxies.

#6

Here is some more on the subject. You can also use the laminate thickness to calculate the Vf or use the Vf to predict the thickness. You can also estimate the porosity of the laminate if you have all the variables.

http://www.compositescentral.com/showthread.php?p=39589#post39589

#7

If it’s just flat 3D woven material and I know the CPT I find this works well…Vf = gsm/(fibre density x cured ply thickness)/10

Any thoughts?