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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The finite element method offers the possibility to study in detail the structures and the research went further by retrieving the data of compressive extension inside the structures, which conducted to the second step. By collecting the data from inside each of the spiral’s nodes gave us an overview of the influence of each individual spiral arm on the displacement of these nodes If we compare the vertical reaction per column of a square pattern, the nodes tend to present a patterned displacement, that is illustrated in the graph (Fig. 9) attributed to the structure from Fig. 8. For a more comprehensive understanding of the displacement in nodes per each column, presented in Fig. 8, the row of 2D spirals indicates the numbering of columns from the structure. 2.7. Digital Image Correlation Method (DIC) Due to the fact that in classical compression tests cannot determine the displacement of each node, was found digital image correlation as an appropriate method for data validation of FEM. This method offered the possibility to view in detail and measure the displacements generated by the applied loads inside the structures (Moreira, 2012). For Digital Image Correlation (DIC) method the software used was VEDDAC (Chemnitzer Werkstoffmechanik GmbH, Germany). This method relates to pixels movement from successive frames (Pan, 2011) and the software has the ability to recognize each new position of pixels, tracking their 2D displacements. During the compression testing of the metamaterial, have been caught scenes of each movement in the structures. The DIC testing starts with a digitized pattern of the undeformed sample, as a reference. On the reference scenes are selected a convenient set of pixels that will change their position when the load is applied (first picture – left from Fig. 10-12).

Fig. 10. DIC images corresponding to different loading steps of compressed sample M1X1

Fig. 11. DIC sequence corresponding to different loading steps of compressed sample M3X1

Fig. 12. DIC sequence of the test specimen subjected to a compressive load and unloading (M3X3)

The reference image of the structure is followed by a set of frames (Fig. 10-12) that caught every movement of the