Laminate resin weight and volume fraction

[jacobe]

Good evening

I have searched all over the net and the forum and cannot seem to find this information, so just before I go to bed I thought I would ask for help.

I have a carbon prepreg that has 50% resin by weight, how do I calculate the fibre volume fraction?

Help would be very appreciated.

Thanks

[marshmat]

VectorLAM, http://vectorply.com/lamdesign/vectorlam_sw.htm can assist in computing this information (along with a lot of other useful stuff). It's tricky to learn, but worth it if you need to design multi-layer laminates.

[jacobe]

Thanks for that I will check it out.

Does anyone have the formula?

[AVMan]

You will first need to know the densities of both the fiber and resin in order to convert from weight fraction to volume fraction. You will also need to know the overall density of the composite (use eqtn. 2 below). Carbon fiber is typically 1.8 g/cc and a typical epoxy resin is around 1.2-1.3 g/cc. Below are the equations used to go between Wf (fiber weight fraction) and Vf (fiber volume fraction). Also note that Wm is the resin/matrix weight fraction and Vm is the resin/matrix volume fraction:

1.) Vf = Wf x (density of composite / density of fiber)

2.) (1/density of composite) = (Wf/density of fiber) + (Wm/density of resin)

Hope this helps.

[jacobe]

Thanks AVMan

Although struggling to get my head round this one and feeling a bit dumb…

This is the data I have:

Carbon fabric - 120gsm
Density of the carbon - 1.73g/cc
Density of the matrix - 1.23g/cc
Matrix is 50% by resin weight
Fibre volume = 120 = 67.796cc
1.77


So to calculate the fibre volume fraction do I need to do the following:

1. Calculate the density of the composite, (Wf/density of fiber) + (Wm/density of resin) = (120/1.73) + (120?/1.23)

2. Calculate the Vf = Vf = Wf x (density of composite / density of fiber) = 120 x (density of composite from 1. / 1.73)

Am I close?

Thanks

[AVMan]

Actually, you're a bit off. Below would be the way to get the fiber volume fraction:

(1/density of composite) = (0.5/1.73) + (0.5/1.23) = 0.6955

so, density of composite = 1/0.6955 = 1.44 g/cc

Vf = (0.5)(1.44/1.73) = 0.42 or the fiber volume fraction is 42%

(note above that the '0.5' values stand for the 50% weight fractions, and we are assuming zero percent void volume).

1.73 g/cc fiber density? Must be working with some intermediate modulus carbon?

[jacobe]

Thanks again AVMan, really appreciate the help here.

Had the density wrong should have been 1.77 working with T300.

Have a good one!