Effects of Build Orientation and Loading Direction on the Compressive Behavior of Additively Manufactured Re-Entrant Auxetic Materials.

Additive manufacturing (AM) technologies, particularly Fused Deposition Modeling (FDM) and Digital Light Processing (DLP), offer viable solutions for producing Auxetic materials characterized by their negative Poisson's ratio. This study investigates the influence of build orientation and loading direction on the mechanical behavior of re-entrant honeycomb auxetic structures fabricated using both FDM- and LCD-based DLP techniques. Specimens were produced in three principal build orientations (X, Y, and Z) and subjected to compression along two directions (X and Y) to capture the anisotropic mechanical response. Standard PLA filament was used for FDM, while standard and tough resins were used for DLP. Uniaxial compression tests were conducted to evaluate maximum compressive stress, Poisson's ratio, and energy absorption behavior. The results reveal significant anisotropy in mechanical performance depending on build orientation and printing technology. DLP-printed specimens exhibited more isotropic behavior compared to FDM due to superior interlayer adhesion. Furthermore, build orientation was found to have a pronounced effect on auxetic response and load-bearing capacity. This study highlights the critical importance of considering build orientation and loading direction during the design and manufacturing of auxetic structures, especially for applications requiring targeted mechanical performance.