PSI - Issue 56

Vasilica Ioana Cimpoies et al. / Procedia Structural Integrity 56 (2024) 49–57 Author name / Structural Integrity Procedia 00 (2019) 000–000

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2.4. Structure description For a better understand of the behaviour of the structure, after developing the model it was found proper to print layers of metamaterials with different number of cells, predicting that the structure will respond with different displacements depending on the number of cells. All the models keep the same dimensions for cells as presented in Fig. 2. For all the models have been added side plates as supports for positioning the samples onto testing machine. The tested samples, as depicted in Fig. 5 and identified by their respective name codes, are as follows: 1. M1X1 – A single cell of the metamaterial featuring side plates, composed of four interconnected spirals. 2. M3X1 – A row of cells with side plates. 3. M3X3 – A square pattern of cells comprising nine complete cells and sixteen spirals, supported by two plates.

Fig. 5. Samples of the metamaterial used for compressive testing (right - M1X1, center - M3X1, left - M3X3)

2.5. Experimental compression test Three different 3D printed samples of metamaterial together with the tensile specimens of Z-ultrat (as mechanical properties reference) have been tested on the universal testing machine (Instron 3366, 10 kN). The samples of metamaterial have been subjected to maximum loads that were able to withstand plastic deformation or fracture. Has been observed that during the experiment the metamaterials have shown a very high extension rate from 8.9% for one-cell model (M1X1), 7.74 % for M3X1 a single row of cells and up to 13.5% for a square pattern with 9 cells (M3X3). All the shapes presented an instant shape recovery of the structure with a precision rate of 99%. Throughout the testing process, it was observed that the material exhibited deformation in two distinct directions, namely, vertical, and horizontal. The horizontal displacement was primarily induced by the spiral arms, resulting in a rotational deflection around the spiral nodes. Notably, the deformation displayed non-uniform characteristics across all structures, as each spiral arm triggered a cascading effect among its neighbouring counterparts. Consequently, initial observations indicate that these structures demonstrate a nonlinear and hardly predictable response when subjected to applied loads.

Fig. 6. Comparison of force vs displacement between the three structures (M1X1, M1X3 and M3X3)