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The stiffness and strength of a composite laminate can be maximised by increasing the volume fraction of fibres in that laminate. The maximum volume fraction of fibres is a theoretical value, as it assumes that the fibres are touching, and takes no account of voids that will be present in the cured laminate.
Volume fraction of fibres in a composite laminate is derived from the fibre-to-resin weight ratio. The calculation relies on data, such as the areal weight and density (⍴) of the fibres, and the density of the resin, that should be provided by the material suppliers.
Determine the weight of fibres (Wf) by dividing the areal weight of the fibres by the area of the ply (layer of fibre).
Weigh the cured laminate.
Subtract the weight of the fibres from the weight of the laminate to determine the weight of the resin (Wr) in the laminate.
Divide the weight of fibres by the fibre density to calculate the volume of fibres, Vf:
Vf = Wf/Wr
The fibre-to-resin volume ratio, Vf/Vr = (Wf/Wr) x ( ⍴r/⍴f)
And the resin volume, Vr = 1/(1+(Vf/Vr))
We can now calculate the theoretical volume of fibres, Vf = 1 – Vr
To account for the volume of voids (Vv) in the laminate, we include another term:
Vf = 1 – Vr – Vv.