Auxetic lattice structures consisting of an enhanced trigram frame unit cell with superior stiffness.

• Two novel auxetic structures with different arrangements of a new enhanced trigram frame unit-cell were proposed. • The mechanical performance of the designed structures was evaluated through theoretical analysis, finite element simulation, and experimental tests. • Single and multi-objective optimization methods were implemented to optimize the geometry parameters of the selected auxetic structure. • The exceptional mechanical characteristics of the present proposed structures, surpassing previous designs in terms of stiffness and specific stiffness, highlight their tremendous potential for load-bearing applications. Superior stiffness is deemed essential for structures intended for several applications. The stiffness enhancement can be achieved by adopting structures that deform based on the stretching-dominated mechanism instead of the bending-dominated mechanism. This paper proposes a novel auxetic unit cell design and two distinct lattice structures dominated by stretching when subjected to quasi-static compressive and tensile loadings. The structures are manufactured via the fused deposition modeling (FDM) 3D printing method with the use of polylactic acid (PLA) filament as the patent material. The investigation also includes theoretical analyses and finite element (FE) simulations, all yielding consistent results. Response Surface Methodology (RSM) is also employed to understand the influence of three geometric parameters. Besides, single-objective optimization is conducted to maximize the stiffness through geometry design, and multi-objective approaches are implemented to improve the stiffness while simultaneously reducing relative density. Finally, different unit cells, which deform based on the stretching-dominated mechanism, are selected to represent their respective classifications, enabling a comparison of their potential stiffness capacity with the designed structures in this study. Remarkably, it is highlighted that the proposed unit cells and structures outperform others in terms of specific stiffness, making them a promising choice for use in structural engineering. [ABSTRACT FROM AUTHOR]