Page 67 - MSAM-2-1

Materials Science in Additive Manufacturing Energy absorption of Moore’s thin-walled structures

Figure 7. Configurations of 3 order structure (relative density of 30%) during compression at different strains. Squares colored green, red, and blue
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show the deformation change of the structure causing stress drops A, B, C, and D, respectively, as highlighted in the stress-strain curve. Magnified images
showing the snap-in behaviors, straightening of curved elements, and failure within the structure.

was observed at compression strains of 40% and 50%, structure through a comparison of their post-mortem
corresponding to stress drops B and C, respectively. The deformations (Figure 8). The deformed shapes of the
basis of the descend after local peak D was the straightening specimens before and after cyclic loading are illustrated
of curved elements and damages within the structure (see in Figure 8. The 2 order structure maintained its original
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yellow magnified images in Figure 7). Compared with shape with a certain degree of contraction, while the
the 1 and the 2 order structures, the 3 order structure 3 order structure experienced significant permanent
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showed a more complex cross-sectional geometry with deformation.
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more concave/convex. Hence, the response of the 3 order
structure demonstrated more drops in stress. 3.2. FE model validation
The FE simulation results were validated by comparing
3.1.2. Cyclic loading test results
to the experimental outcomes in terms of the effective
As observed from the results of the quasi-static compression stress-strain curves of the fractal structures with a
tests, the 2 and 3 order metamaterials with relative relative density of 20% (Figure 9). The behaviors from
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density of 20% revealed their characteristic compliance numerical simulation were close to what was observed
feature. Hence, a cyclic compression test with six loading- from the experiment. However, there were still some
unloading cycles was performed to further investigate the discrepancies. Figure 9 presents the effective stress-strain
energy absorption performance of fractal-inspired thin- curves from the experiments and simulations. In general,
walled structures. Figure 8 shows the effective stress-stain the strain and stress predicted from numerical models
curves for both 2 and 3 order structures under cyclic were higher than those captured in experiments. In the
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loading from direction 1 and 2. Overall, for each design, simulation, there was no obvious sliding between rigid
the response of the first cycle was different from the plates and fractal structures. Nevertheless, the top and
following five cycles. The structure behaved in a similar bottom of the fractal structures that were in contact with
way during the last five cycles regardless of the loading the metal compression plates slipped along the tangential
direction, demonstrating the reliability and recoverability direction. Despite applying a frictional penalty of 0.3 to the
of the structures to some extent. In other words, most of tangential interaction between surfaces in the FE model,
the plastic deformation during the whole cyclic loading the coefficient of friction between the metal plates and the
test occurred in the first cycle . fractal structures during experiment seemed to be smaller.
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Besides, the 2 order structure appeared to have The sliding attributed to the lower strain and stress in the
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higher recoverability after cyclic loading than the 3 order experiment compared to the simulation.
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Volume 2 Issue 1 (2023) 8 https://doi.org/10.36922/msam.53