Characterization of 2D PLA Structural Metamaterials-Methodology and Challenges for Properties Assessment.

Mechanical (or structural) metamaterials offer a paradigm shift in the mechanical response of advanced structures, achieving performance distinct from their base material through architected unit cells that geometrically tailor stress distribution. Characterising these structures demands methodologies capable of capturing localised deformations while reconciling numerical predictions with as-manufactured behaviour. This study introduces a Digital Image Correlation (DIC) based methodology for the mechanical characterisation of three two-dimensional PLA lattice metamaterials, produced by material extrusion (MEX) and selected from a computational screening of approximately 57,000 candidate geometries to span the negative, zero and positive Poisson's ratio regimes. Predicted and measured Poisson's ratios agreed to within 0.01 across all three geometries without correction, whereas structural rigidity deviated substantially from nominal geometry predictions. A targeted correction strategy, using micro-computed tomography (µCT) to measure wall thickness at high-stress concentration zones identified through finite element modelling, reduced these deviations from 46% to 7% for the auxetic geometry, and from 25% to 2% for the positive Poisson geometry. These results show that Poisson's ratio and rigidity respond differently to manufacturing-induced dimensional deviation, and that efficient, targeted geometric correction, rather than full model reconstruction, is sufficient to reconcile numerical and experimental behaviour for these structures. This approach offers a practical framework for the experimental evaluation and numerical validation of mechanical metamaterials.