Effect of Nozzle Diameter on Mechanical Properties and Microstructure of Fused Deposition Modeling 3D Printed Polylactic Acid Parts

Fused deposition modeling (FDM) is one of the most common additive manufacturing techniques, but the mechanical performance of 3D printed components depends strongly on printing parameters. This study investigates the effects of nozzle diameter on tensile strength, elastic modulus, and microstructure in 3D printed polylactic acid (PLA) specimens. Samples were fabricated using a range of nozzle sizes from 0.2mm to 0.5mm diameter and tested under uniaxial tensile loading until failure. The results show an increase in ultimate tensile strength and Young's modulus with increasing nozzle diameter. Scanning electron microscopy reveals enhanced interlayer adhesion for larger nozzle sizes, with a transition in fracture mode from interlayer to intralayer dominated. To further understand these findings, anisotropic constitutive models were developed to predict the mechanical properties of PLA. These models were derived using principles of composite laminate theory, which consider the effects of nozzle diameter on the material coherence between printed layers. The theoretical predictions made by these models were compared with the experimental data, showing a good agreement and providing deeper insight into the relationship between printing parameters and mechanical performance. The experimental and analytical results both highlight nozzle diameter as a critical factor determining achievable mechanical properties in FDM. This work provides insights into the key relationships between processing, structure, and properties, which can guide component design and process optimization in 3D printing of thermoplastic polymers.