On the Design and Characterization of an Auxetic Wearable Pad
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This study presents a combined experimental and numerical approach to derive guidelines for tuning the design of an auxetic wearable pad intended for topical skin treatment. The pad structure is based on the sinusoidal ligament unit cell. Key geometric parameters governing the unit-cell shape have been identified, and a parametric digital model of the pad structure has been developed. Starting from this parametrization, multiple pad configurations were generated and analysed both numerically and experimentally under tensile loading. Moreover, additional samples were designed for testing under biaxial loading conditions to further deepen the deformation mechanisms of specific auxetic configurations. The deformation mechanism of each configuration has been analysed to investigate the influence of the selected geometric parameters on the auxetic response, with particular attention to their influence on Poisson’s ratio (i.e., the local transverse to axial strain negative ratio at the level of the unit cell). The physical specimens were fabricated via Fused Filament Fabrication (FFF) using Polycaprolactone (PCL) and a lab-developed bioactive composite filament (PCL-collagen peptides). For the experimental tests, dedicated image-based acquisition systems have been conceived and applied. Results show that the unit cell node undergoes initial straightening of the sinusoidal ligaments through rotation of the intersection nodes, followed by the stretching of the ligaments. Indications on how the selected geometric parameters influence the structure's deformation and mechanical response have been obtained. Furthermore, the effectiveness of the manufacturing process, i.e., the fidelity of the printed patch, for different geometrical features was also assessed. Overall, the collected insights provide guidance not only on fine-tuning the auxetic wearable pad design but also highlight relevant theoretical and practical aspects concerning characterizing the behaviour of auxetic designs based on the sinusoidal ligament unit cell.
