Influence of porosity and architecture on the mechanical and acoustic properties of FFF ‐printed PLA structures

Abstract This study investigates the influence of porosity and infill architecture on the mechanical and acoustic properties of poly(lactic acid) (PLA) structures fabricated by fused filament fabrication (FFF). Controlled variations in infill density (100%, 95%, 90%, 85%, and 80%) and infill pattern (line, combined, and concentric) were used to generate different levels of porosity and internal architectures. The volumetric porosity of every specimen was measured independently from its apparent density rather than taken from the nominal infill setting. Ultrasonic measurements performed along three orthogonal directions, combined with mechanical compression tests, reveal a strong dependence of elastic properties on both porosity and structural orientation. A pronounced anisotropic behavior is observed, highlighting the role of filament alignment and interlayer interfaces. The results show that ultrasonic wave velocities decrease with increasing porosity, in agreement with theoretical predictions at low porosity, while significant deviations appear at higher porosity levels due to microstructural heterogeneity. The comparison between ultrasonic and mechanical Young's moduli demonstrates a transition in the ratio, reflecting the influence of porosity, interlayer defects, and measurement scale. These findings provide new insights into the structure–property relationships of additively manufactured polymers and highlight the critical role of interlayer porosity in governing the mechanical and dynamic behavior of FFF‐printed PLA structures. This three‐direction measurement strategy enables a comprehensive assessment of anisotropic behavior, allowing the distinction between in‐plane and through‐thickness responses, directly linked to filament orientation and interlayer porosity. © 2026 The Author(s). Polymer International published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.