Microstructural alteration and its impact on the effective stiffness of short carbon fiber-reinforced PLA in fused deposition modeling

This study investigates the change in microstructure of short carbon fiber-reinforced polylactic acid (CF-PLA) filaments during fused deposition modeling (FDM) printing and its impact on the effective elastic modulus of printed parts. A comprehensive experimental protocol is employed, including thermogravimetric analysis (TGA), photomicrography, and micro-computed tomography (µ-CT) to characterize key microstructural parameters such as fiber volume fraction, aspect ratio, and fiber orientation distribution. Additionally, uniaxial tensile tests are performed on specimens printed in three raster orientations (0°, ±45°, and 90°) to characterize mechanical response. The experiments reveal significant fiber misalignment, fiber breakage, and matrix degradation during FDM printing, all contributing to a substantial reduction in Young’s modulus.

To interpret the experimental observations, two novel tri-scale homogenization models (Mori-Tanaka-Finite Element and Fully Finite Element) were developed, integrating micro-, meso-, and macro-scale data to predict effective stiffness with errors below 5% and 7%, respectively, across various raster orientations. A key innovation in this framework is the introduction of a degradation parameter to account for matrix deterioration during printing. Parametric studies identified fiber breakage as the most significant factor, causing a 27.15% stiffness loss, followed by misalignment (15.54%) and matrix degradation (10.74%). This holistic framework, combining experimental and computational approaches, elucidates process-structure–property relationships, offering a new insights about FDM-printed short fiber-reinforced composites for structural applications.