Analysis of additively manufactured (3D printed) dual-material auxetic structures under compression

Auxetic cellular structures offer improvements in some mechanical properties due to their negative Poisson's ratio response when loaded. This study investigates and compares the effect of using multiple materials within three well researched cellular geometries, two auxetic: re-entrant and anti-tetrachiral, and one non-auxetic: hexagonal honeycomb. For each geometry, three different material configurations were used, a single material PLA structure and two dual-material structures: Polylactic Acid (PLA)-Nylon and PLA-Thermoplastic Polyurethane (TPU). A numerical model was developed to simulate these complex multi-material cellular geometries under a quasi-static compression load using Abaqus Explicit solver. To validate this numerical model, samples were additively manufactured and experimentally tested. They were found to show good correlation for the PLA and PLA-TPU. This study found that for situations where single loading cycles were required, for example, for crashworthy structures, the single material structures offered the highest performance where they absorbed the largest amount of energy. If multiple loading cycles are required, the multi-material structures offer the best solution due to the compression occurring through elastic buckling in comparison to plastic buckling in the single material. It was also found that through introducing materials with varying stiffnesses into specific regions within the structure, the Poisson's ratio through the compression could be modified for the re-entrant and honeycomb geometries.