Impact of Varying Fiber Angles and Post-Heat Treatment on Tensile Mechanical Properties of Unidirectional and Bidirectional 3D Printed Composites

This study investigates the impact of varying fiber angles on tensile mechanical properties of unidirectional [0°]¹⁶, [45°]¹⁶, [90°]¹⁶ and bidirectional [0°/45°]⁸, [45/90°]⁸, [0°/90°]⁸ carbon fiber-reinforced 3D-printed composites. Moreover, the impact of post-heat treatment on tensile properties of unidirectional and bidirectional composites was investigated. Results demonstrated that unidirectional pure-composites at [0°]¹⁶ fiber angle achieved higher tensile strength of 204.09 MPa and modulus of 13.05 GPa than [45°]¹⁶ and [90°]¹⁶ fiber angles, owing to [0°]¹⁶ fiber angle arranged parallel to loading direction and transfers the majority of tensile load, resulting in fiber-dominated failure. Bidirectional pure-composites at [0°/45°]⁸ fiber angles attained higher tensile strength of 194.44 MPa and modulus of 11.65 GPa compared to [45/90°]⁸ and [0°/90°]⁸ fiber angles, as [0°]⁸ is positioned parallel and carries load directly, whereas [45°]⁸ is set diagonal and transfers load partially, leading to combined fiber and shear failure. After post-heat treatment at 200°C, [0°]¹⁶ unidirectional composite exhibited the highest tensile strength of 253.69 MPa and modulus of 16.66 GPa, in contrast to other unidirectional composites, and [0°/45°]⁸ bidirectional composite offers the greatest tensile strength of 221.88 MPa and modulus of 12.71 GPa compared to other bidirectional composites. Microstructural examinations confirmed that fiber and matrix were consolidated because of better wettability, enabling matrix fusion effectively as material extrusion-induced pores were eradicated, confirming the development of robust fiber-matrix interface bonding, thereby considerably improving overall mechanical performance. However, this study is limited to tensile properties. This study provides valuable design insights for manufacturing high-strength 3D-printed components for aircraft and structural applications.