Microstructure and mechanical properties of filament and fused deposition modelling printed polylactic-acid and carbon-fiber reinforced polylactic-acid

Fused deposition modelling (FDM) is a popular additive manufacturing method involving the deposition of a molten filament along a specific path. In this paper, the microstructure and properties of the filament and the printed part are compared to understand the microstructure and property evolution during the printing process. Two commonly used materials Poly-lactic acid (PLA) and carbon fiber-reinforced PLA (CF + PLA) are used for the study. A thorough experimental campaign is undertaken to compare different properties including elastic properties (modulus, ultimate tensile strength, strain to failure), fiber length distribution, fiber orientation distribution, X-ray diffraction (XRD) analysis, and multiscale characterization of damage/mode of failure. The addition of CF reinforcement led to an increase in Young’s modulus and a reduction of the tensile strength for both the filament as well as printed coupons. There is extensive microstructural change during the printing process with major fiber breakage and increased misalignment. In general, Young’s modulus of the printed part is significantly lower than the filament whereas the strength depends on the printing orientation. Both the filament and printed part display complex modes of failure at multiple length scales. The damage modes for the filament and corresponding printed part are different with a strong dependence on the raster orientation for the latter. XRD confirms somewhat different amorphous behavior for the filament and printed part.