Porosity-Impact Strength Relationship in Material Extrusion: Insights from MicroCT, and Computational Image Analysis

Additive Manufacturing, also known as 3D printing, has transformed conventional manufacturing by building objects layer by layer, with material extrusion or fused deposition modeling standing out as particularly popular. However, due to its manufacturing process and thermal nature, internal voids and pores are formed within the thermoplastic materials being fabricated, potentially leading to a decrease in mechanical properties. This paper discussed the effect of printing parameters on the porosity and the mechanical properties of the 3D printed polylactic acid (PLA) through micro-computed tomography (microCT), computational image analysis, and Charpy impact testing. The results for both tests were correlated to investigate the relationship between porosity and Charpy impact strength. PLA samples of 1 cm³ × 1 cm³ × 1 cm³ were 3D printed at printing temperatures of 180°C, 200°C, 220°C, and 240°C, and at printing speeds of 50, 80, and 110 mm/s, while porosity was measured from microCT-reconstructed data. Additionally, impact strength was assessed using a notched Charpy impact tester following ASTM D6610-18. In general, results show that higher printing temperatures and lower printing speeds reduced pore size by improving material flow and fusion, while also increasing impact strength due to better thermal bonding and interlayer adhesion. A maximum 36.8% reduction in mean pore size and a 114% improvement in impact strength were observed at 110 mm/s and 220°C. Conversely, increasing printing speed led to lower Charpy impact strength. Optimal impact behavior and minimal voids were observed at a printing temperature of 220°C and a printing speed of 50 mm/s.