Experimental characterization and micrography of 3D printed PLA and PLA reinforced with short carbon fibers

The objective of this work is the mechanical characterization of materials produced by 3D printing based on fused filament fabrication (FFF, analogous to FDM®). The materials chosen are a polylactic acid (PLA) and a PLA reinforced with short carbon fibers in a weight fraction of 15% (PLA+CF). In view of the FFF nature, which produces specimens layer by layer and following predefined orientations, the main assumption considered is that the materials behave like laminates formed by orthotropic layers. If the 3D printing is made in the 1−2 plane, where 1 is the deposition direction and 2 is a direction perpendicular to 1, the mechanical properties obtained are the tensile moduli E1 and E2, the Poisson ratios ν12 and ν21, the shear modulus G12 and related strength properties. For this purpose, only unidirectional or specially oriented specimens are used. After tests up to material failure, scanning electron microscopy (SEM) is employed to observe fracture surfaces. It was noticed that, in the microstructure of the PLA+CF, the short carbon fibers stay highly oriented with the material deposition direction in the FFF specimens. This fact, and the also observed length of the fibers, explains differences in material properties encountered among the performed experiments.