Issue 77

L. Marsavina et alii, Fracture and Structural Integrity, 77 (2026) 107-119; DOI: 10.3221/IGF-ESIS.77.08

deformation level which, in practice, is never reached by the E.a inspired structure due to the brittle fracture that intervenes first. The E.a inspired architecture suppresses buckling and move the material failure mode from geometric instability to material failure. Post-buckling analysis made it possible to quantitatively evaluate the change in stiffness, calculated as the ratio between the applied displacement and the calculated reaction force in the lower contact region, associated with the buckled configuration This was achieved by using the deformed shape corresponding to the critical displacement as the initial geometry for a subsequent multi-step nonlinear static structural analysis. Fig. 7 illustrates the stiffness variation for each lattice structure in the buckled state. It can be observed that, for both the square and triangular lattice structures, an instantaneous deviation from an initially constant stiffness value occurs as a direct consequence of buckling. In contrast, the E.a.-inspired structure exhibits a continuously varying stiffness throughout the entire simulation, without a clearly defined plateau region. Finally, the reaction force leading the specimens to failure was calculated by FEM model extracting the reaction force value estimated in correspondence of the experimental displacement leading the specimens to failure in the post-buckling analysis. Comparison with experimental tests It is possible to compare the results coming from the experimental compressive tests with the prediction of the FE simulations of compression failure and buckling. In Fig. 8, for each lattice structure, the diamonds represent the average value of experimental compression failure force, calculated by the points represented by circles and followed by error bars representing the standard deviation of the samples in force and relative density on four specimens. The “x” marker points indicate the failure load estimated by FE models, extracted in correspondence of experimental failure displacements; finally, the squares represent the critical forces causing buckling estimated by non-linear eigenvalues buckling analysis.

Figure 8: Comparison of experimental test with FE simulations.

For the square-lattice, the experimental failure has higher value ( 938±135 N) compared to the compression (374 N) and buckling (208 N) loads estimated by FEM. The difference is more marked considering the triangular-lattice and E.a. inspired structure; indeed, the first has a failure load of 2980±184 N, a compression load of 1639 N and a buckling load of 903 MPa, while the latter has a failure load of 4887±161 N, a compression load of 3793 N and a buckling load of 3394 MPa. The difference between the compression load and the buckling load of the triangle lattice seems more pronounced since the buckling phenomenon interest a large part of the sample; on the other hand, in the square lattice and E.a. inspired structure it involves smaller area of the specimens (Fig. 6). Another explanation to the increase in critical displacement, and consequently of critical load, is that each structure’s unit cell can be seen as a square unit cell reinforced with diagonals struts, and these reinforcements influence both critical and fracture load. The under estimation of experimental failure loads

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