Influence of mixed isotropic fiber angles and hot press on the mechanical properties of 3D printed composites

Abstract This paper aims to study the mechanical properties of mixed isotropic carbon fiber 3D printed composites and further investigates the influence of hot press on the [0°/45°/90°]2 fiber angles composite with varying temperature, pressure and time. Tensile tests, autoclave treatment and microstructural observation were utilized to characterize the composites. Results revealed that the [0°/45°/90°]2 performed the highest tensile strength of 79 MPa and modulus of 3.51 GPa, compared to [30°/45°/60°]2 and [15°/45°/75°]2. This is due to the fibers along the tensile axis angle that bears maximum load in longitudinal direction. At 200 °C temperature, the hot pressed composites presented the highest tensile strength of 98 MPa and modulus of 3.93 GPa than non-hot pressed. Increased temperature caused better interface wettability between fibers and matrix. At 200 kPa pressure, the hot pressed composites showed the highest tensile strength of 100 MPa and modulus of 4.06 GPa than non-hot pressed. Further increased pressure resulted in lower tensile strength and modulus, as the material became stiffer pushing more matrix material to side leaving numerous fibers unbounded by the matrix. For 30 min withholding time, the hot pressed composites indicated the highest tensile strength of 106 MPa and modulus of 4.27 GPa than non-hot pressed. Increased time caused strongest interface bonding by removing the air gaps induced during printing between fibers and matrix. Results revealed that hot press significantly improved the mechanical properties of carbon fiber 3D printed composites.