Influence of layer orientation on the mechanical properties of fused deposition modelling using PLA and PETG

The rapid advancement of Fused Deposition Modelling (FDM) technology has enabled researchers to optimise processing parameters and enhance the performance of thermoplastic components. However, the anisotropic behaviour induced by the layer-by-layer deposition process requires a comprehensive understanding of the mechanical response and failure mechanisms. This study investigates the mechanical properties and fracture behaviour of polylactic acid (PLA) and polyethylene terephthalate glycol (PETG) specimens fabricated using FDM, with print orientations of [$0°$], [$\pm 45°$], and [$90°$]. By treating the printed structures as orthotropic materials, characterisation was conducted following the ASTM D3039 and ASTM D3518 standards, which represent a key methodological contribution of this work. Uniaxial tensile tests were performed in conjunction with Digital Image Correlation (DIC) to determine elastic moduli, Poisson’s ratios, and tensile strength. PLA exhibited 21.1% higher maximum tensile strength than PETG in the [$0°$] orientation. Conversely, PETG outperformed PLA in the [$90°$] and [$\pm 45°$] orientations, with 13.7% and 12.3% higher strength, respectively. Post-failure analysis using optical microscopy and scanning electron microscopy (SEM) revealed brittle fracture features in PLA and ductile behaviour in PETG, with filament rupture for layers at 0$°$ and filament detachment for 45$°$ and 90$°$. Therefore, Hashin’s failure criteria predictions were confronted with experimental data, showing agreement with not only strength values but also associated failure mechanisms. These findings contribute to the understanding of anisotropic mechanical performance in FDM-fabricated polymers, providing insights for performance-oriented design in FDM applications.