Effects of a rotary shear field on the interlayer bond and mechanical properties of carbon-fiber-reinforced plastic composites fabricated using fused deposition modeling

One of the key issues restricting the wider application of parts fabricated by fused deposition modeling (FDM) in various fields is the lack of interlayer bonding, owing to layer-by-layer deposition. This issue results in poor mechanical properties and strong mechanical anisotropy of FDM-printed parts. Moreover, this is more critical for FDM-printed parts made of fiber-reinforced composite materials. In this study, an innovative FDM 3D printer with a rotary print head was developed to enhance the tensile strength of parts fabricated from short carbon fiber (CF)-reinforced polylactic acid (PLA) composites. The rotary speed of the print head was a dominant parameter affecting the tensile properties of the parts. The optimal rotary speed was at 200 rpm at a raster angle of 0°, which offered a 1.5-fold enhancement in the tensile strength and 6-fold reduction in anisotropy. In addition, a rotary speed of 200 rpm caused greater entanglement of the polymer chains, whereas increasing the speed to 300 and 400 rpm led to less entanglement. Notably, the rotary shear field provides “in situ” regulation of microstructure formation during the 3D printing process. The results of this study can be useful in enhancing the mechanical strength and reliability of industrially manufactured FDM parts.