Preparation of fixed length carbon fiber reinforced plastic composite sheets with isotropic mechanical properties

Molded carbon composite sheets with different fiber volume fractions were prepared by dispersing fixed length (30 mm) carbon fibers in a vinyl resin matrix, which was then made into a carbon fiber reinforced polymer (CFRP) composite sheet by vacuum hot-pressing. The influence of the volume fraction (15%–40% (vol.)) of the carbon fibers on the tensile and bend strengths, and the in-plane isotropic characteristics of mechanical properties of the composites were investigated. Results show that the tensile strength in different in-plane directions of the composites varied by only 2%-3% at a 25%-30% (vol.) fiber content, indicating that the carbon fibers are well dispersed in the resin, and composite sheets with these fiber volume fractions are isotropic in the plane. By increasing the carbon fiber volume fraction from 15% to 40%, the composites had a maximum tensile strength of 141.4 MPa at 25% fiber volume and a maximum bend strength of 549.0 MPa at 30% fiber volume, which are respectively 112.8% and 129.6% higher than the values at a fiber volume fraction of 15%.