Designable Mechanical Properties of 3D Printing Composites with Multiple Filaments by Different Infill Percentages and Structures

The current study reports the mechanical properties of 3D printing using multiple composite filaments, infill percentages, and printed structures. Results show that graphene-contained polylactic acid (G-PLA) displays the highest bending strength, of 119.50 MPa, improving by 62.7%, compared with pure PLA. The scanning electron microscopy (SEM) microstructural observations indicate that the high bending strength is caused by the pull-out of graphene. As for the double-filament layer-by-layer alternatively printed specimens, the obtained bending strengths are between the single-filament specimens printed by the two filaments, respectively. Changing infill percentages from 30%, 65%, and to 100% prove that the mechanical properties are greatly enhanced. In the bending tests, with an increase in the infill percentage from 30% to 100%, it is found that all the bending strengths of G-PLA, copper powder-containing polylactic acid (Cu-PLA), and carbon fibers-containing C_f-PLA increase by 63.7%, 130.1%, and 106.6% on account of enlarged cross-section areas sustaining stress. Furthermore, in the compressive tests, shear stress is only found in the hexangular structure, which has a positive effect on the 32.1% increase of the compressive strength compared with that in the rectangular structure. It implies that printed structures significantly influence the fractured modes due to the variation of stress distribution in the designed structures.