Tensile Performance and Structural Optimisation of FDM-Printed PLA Components with Different Infill Structures

Abstract

Fused Deposition Modelling (FDM) is one of the most widely adopted additive manufacturing technologies, and polylactic acid (PLA) has emerged as a commonly used feedstock material owing to its biodegradability and low cost; however, the mechanical performance of FDM-printed PLA components is significantly influenced by their internal infill structure. This study systematically investigates the design of infill structures in 3D-printed PLA components with the dual objectives of minimising structural mass while maximising mechanical strength. Standard tensile specimens with three infill topologies-honeycomb, grid, and triangular-at three infill density levels (20%, 40%, and 60%) were fabricated and subjected to uniaxial tensile testing, while three-dimensional nonlinear finite element models were concurrently developed in ABAQUS to simulate their tensile response. The experimental results demonstrate that the tensile strength and Young’s modulus of the honeycomb structure increase continuously with increasing infill density, with the honeycomb topology exhibiting the highest tensile strength across all density levels. Its Young’s modulus increases from 0.180 GPa at 20% density to 0.540 GPa at 60% density, representing a 200% increase; the Young’s modulus of the grid structure increases monotonically with infill density, reaching its maximum at 60% density; whereas the Young’s modulus of the triangular structure is highest at 20% density and decreases with increasing density, a trend potentially associated with topology-dependent stress concentrations and manufacturing-induced micro-defects at higher infill densities. The finite element results show good agreement with the experimental data, with maximum relative errors of 1.39% for peak load and 10.81% for fracture displacement, indicating the predictive capability of the model within the investigated parameter range. The honeycomb structure exhibits the best overall performance across the investigated density levels and achieves the highest specific strength at low density. Building on these findings, the infill structure was further optimised using a Kriging surrogate model in conjunction with the Non-dominated Sorting Genetic Algorithm II (NSGA-II), yielding a high-quality Pareto front. The optimisation results identify the honeycomb structure with an infill density of 0.378 as the recommended trade-off solution, achieving a 62.2% reduction in nominal material usage while retaining approximately 80.0% of the tensile strength of the solid reference. Based on the experimental, numerical, and optimisation results, four categories of engineering design guidelines are proposed, covering infill structure selection, optimal density range, scenario-based application, and gradient infill design, providing both theoretical support and practical guidance for the performance-driven design of 3D-printed PLA components for lightweight applications in aerospace, automotive, and related industries.