Design, additive manufacturing, and mechanical characterization of Hastelloy X auxetic metamaterials using interconnected dimpled sheets

To address the demand for lightweight, energy-absorbing structural components, there is a growing need to develop auxetic mechanical metamaterials, which are characterized by a Negative Poisson’s Ratio (NPR) and exhibit unique kinematic responses that provide enhanced shear resistance and fracture toughness. This study examines the mechanical response and auxetic characteristics of a novel three-dimensional lattice architecture derived from mutually connected dimpled sheets. Samples possessing discrete wavelengths of 4, 6, and 8 mm were produced from Hastelloy X using laser powder bed fusion. Evaluation of mechanical properties integrated tensile experiments with Digital Image Correlation (DIC), whereas the as-produced geometric precision was evaluated through in-situ Computed Tomography (CT). The resulting data set indicates an inverse correlation between the structural wavelength and the ultimate load capacity of the metamaterial. The 4 mm configuration supported the maximum load of roughly 99 kN with substantial plastic deformation but did not reach an NPR, as high flexural stiffness resulted in a positive Poisson’s ratio. Conversely, the 8 mm and 6 mm architectures demonstrated abrupt structural failure at reduced peak loads but provided consistent NPR characteristics. Analysis via CT scanning explicitly linked geometric precision to mechanical consistency, revealing that substantial discrepancies from the nominal thickness severely degraded the stability and magnitude of the auxetic mechanism. Full-field kinematic mapping through DIC confirmed that the lateral expansion of the 8 mm geometry created a severe compliance mismatch at the solid boundaries, leading to premature multi-axial shear failure. Ultimately, topological scaling strictly dictates auxetic activation thresholds, while localized material buildup rigidifies compliant hinges to cause premature failure.