Effect of Relative Density in In-Plane Mechanical Properties of Common 3D-Printed Polylactic Acid Lattice Structures

Lattice structures are employed as lightweight sandwich cores, supports, or infill patterns of additive manufacturing (AM) components. As infill structures, the mechanical properties of AM parts are influenced by the infill pattern. In this work, we present the mechanical characterization of three commonly used infill patterns in AM, triangular, square, and hexagonal, and compare them with analytical and numerical models. Fused filament fabrication of polylactic acid (PLA) thermoplastic is used as the printing material for the compressive and tensile tests. First, a parametric analysis is performed by changing the infill density to obtain numerically and analytically the mechanical properties of the studied samples. Next, we compare the experimental results with numerical and analytical models and propose numerical correlations for high-density honeycombs. The stiffest infill pattern was the square, and the explanation is provided in detail. Also, there is a nonlinear correlation between density and the mechanical properties; however, the strongest part was not possible to determine with a significant statistical value. Finally, we propose simplified models for predicting the compressive and tensile response of AM PLA structures by considering the infill regions as homogenized structures.