Full-process Multi-Scale Morphological and Mechanical Analyses of 3D Printed Short Carbon Fiber Reinforced Polyetheretherketone Composites

3D printed short carbon fiber reinforced thermoplastic (SCFRTP) composites have complex multi-scale mor-phologies. These morphologies significantly affect the mechanical properties of SCFRTP. However, the existing research on multi-scale structural morphology formation and multi-scale mechanical responses of 3D printed SCFRTP composites is obviously insufficient so far. Herein, full-process multi-scale morphological and me-chanical analyses of 3D printed SCFRTP composites are conducted in depth. Initially, the SCFRTP composites with the special engineering plastic polyetheretherketone (PEEK) as matrix and short carbon fiber (SCF) as filler (SCF contents of 1 wt%, 3 wt%, 5 wt%, 7 wt% and 10 wt%) are manufactured by 3D printing based on the principle of fused deposition modeling. The multi-scale structural morphologies of these composites are sys-tematically characterized. Then, theoretical investigations are conducted to describe the flow behavior, crys-tallization and viscosity changes during 3D printing molding process, as well as the conservation of mass, momentum and energy for SCF/PEEK composites. The fluid-solid interaction numerical model is established to analyze the printing process of SCFRTP composites. Based on this model, the multi-scale morphologies of 3D printed SCFRTP composites are predicted, and the generation mechanism of multi-scale void defects in 3D printed SCFRTP composites is clarified. Subsequently, the multi-scale mechanical analysis of 3D printed SCFRTP composites is performed to predict the mechanical parameters of micro-traces, the performances of meso-layers and the mechanical properties of macro-3D printed SCFRTP specimens. The full-process from generation in manufacturing to evolution under tension of multi-scale void defects is described by the proposed model. The deviation between the experiment result and the numerical prediction which takes multi-scale void defects and fiber probability density distributions into account is much smaller compared with numerical results ignoring the multi-scale structures. Therefore, the full-process multi-scale analysis method proposed in this paper is of great significance to accurately predict the mechanical properties of 3D printed SCFRTP composites.