The Effect of Design and Fabrication Parameters on the Mechanical Properties of 3D Re-Entrant Honeycomb Auxetic Structures

Abstract

In recent years, the potential of application of auxetic structures, with negative Poisson's ratio, is gaining interest due to the increasingly widespread use of additive manufacturing. Additive technologies allow the manufacture of lightweight and complex shapes, and among them, auxetic cellular three-dimensional structures stand out for their unique behavior and with applications of interest in fields such as aerospace, medical or construction engineering. In the present work, 3D re-entrant honeycomb auxetic structures are designed and manufactured with Stereolithography (SLA) and Fused Filament Fabrication (FFF) with different geometrical parameters to analyse their impact in the mechanical behaviour of these complex structures. To this aim, an Ultimaker S5 and a Formlabs Form3 printer, respectively, have been used. Design variations are approached considering the following parameters: the length of the vertical strut (H), the length of the re-entrant strut (L), the re-entrant angle between the re-entrant and the vertical strut (θ) and the diameter of the struts cross sections (d). The designed structures shape behavior is evaluated with mechanical tests including compression tests and digital image correlation technique, and numerical simulations, The results show that lower Poisson ratio’s values are identified with slimmer profiles and with higher effective lengths and, therefore, corresponds to slender struts. On the other hand, lower angles between vertical and oblique struts show lower Poisson ratios, associated to the load distribution and its effect on the structure’s node displacements.