Effect of compaction pressure on void content and mechanical properties of unidirectional carbon fiber-reinforced epoxy composites prepared by 3D printing

This study investigates the effect of compaction pressure on void content, resin infusion and mechanical properties of unidirectional 3D-printed continuous carbon fiber (CF)-reinforced epoxy composite (CFRC) laminates. The CFRC laminates were prepared using CF tows in a specially designed head for the automated tow placement. Three different compaction pressure (CP), viz., 6, 8, and 11 MPa, were applied on the tows during 3D printing to study the effect of CP on the laminates' void contents and mechanical properties. The void content decreased from 1.83 +/- 0.16 vol% for 6 MPa CP to 0.38 +/- 0.23 vol% for 11 MPa CP, the resin infused to a greater extent, and the strength improved significantly. The 11 MPa CP composite laminates with similar to 60 vol% carbon fibers showed the least void content and the best mechanical properties, i.e., tensile strength and modulus of 2080 +/- 19 MPa and 121 +/- 3 GPa, compression strength and modulus of 570 +/- 15 MPa and 31 +/- 3 GPa, respectively, and inter-laminar shear strength (ILSS) of 64.4 +/- 1.89 MPa. Further investigations on the effect of gaps and overlaps on tensile properties of CFRC fabricated using the CP of 11 MPa suggested that the gaps decreased the strength significantly while the overlaps only marginally affected the strength of laminates. Numerical simulations conducted on the unidirectional CFRC with the same fiber content using finite element analysis revealed that the numerically obtained values are only marginally higher than that of the experimentally obtained results.