PSI - Issue 79

Alessandra Ceci et al. / Procedia Structural Integrity 79 (2026) 73–80

78

load. Densification starts at about 60% strain, where the load sharply increases. Although the load-bearing capacity is limited due to the low relative density, the porous configuration retains the typical three-stage behavior of cellular materials, ensuring efficient energy dissipation under large deformations. For the denser configuration (Structure 2), additional compression parameters were extracted due to the absence of a clear collapse plateau and the earlier densification stage. These values allow a direct comparison with Structure 1, emphasizing the influence of porosity and morphology on the compressive mechanical properties. Table 3. Characteristic compression parameters of the three specimens of Structure 2: For each specimen, the following are reported: the extension of the initial elastic stage and the corresponding load ( ε linear , L linear ), the maximum load reached before the onset of the collapse plateau ( ε p1 , L p1 ), the average plateau load (L pl ), the strain at which densification begins ( ε den ) and the corresponding load measured at 60% strain (L den,60% ). Specimen ε ������ (%) L ������ ���� ε �� ( % ) L �� ���� L �� ���� ε ��� ( % ) L ��� , �� % ���� 1 8 50 30 104 100 60 82 2 10 46 - - - 55 148 3 7 50 33 118 116 60 138 As reported in Table 3, Specimens 1 and 3 show a distinct collapse plateau with average loads around 104–118 kN, followed by densification at ~60% strain. Specimen 2 hasn’t shown a well-defined plateau: the load increases continuously, with densification starting slightly earlier ( ≈ 55%) and the highest load being recorded at 60% strain (~150 kN). 3. Results and Discussion Based on the load–strain curves reported in section 2, the corresponding stress–strain curves were derived dividing the load by the external cross-sectional area of the cylindrical specimens. It should be emphasized that the actual load bearing area of the lattice is smaller, since part of the volume is occupied by pores and cavities. Nevertheless, the use of the external area is a standard practice for cellular materials (Ashby et al., 2000), as it allows direct comparison with literature data and makes the definition of stress independent of internal morphology. These curves allow the identification of the main deformation stages typical of cellular materials and are the basis for the calculation of the specific energy absorption (SEA). The comparative analysis between the two structural configurations highlights the influence of relative density on the collapse mechanisms and energy dissipation capability. Fig. 6 shows the stress– strain curves for the two structures. For Structure 1, the collapse plateau stress is well defined and relatively stable, although interrupted by local peaks. Densification occurs at around 70% strain, confirming that this configuration can withstand large deformations while maintaining energy dissipation capability. For Structure 2, the behavior is markedly different. The curves display a continuous and regular load increase without a well-defined plateau, indicating that the denser morphology offers more uniform resistance to deformation but with a lower energy absorption capacity. Deformation is governed mainly by gradual plastic yielding rather than progressive strut buckling. The specific energy absorption (SEA) was calculated by integrating the area under the stress–strain curves up to a defined strain level. The total energy absorbed by the specimen is given by Eq.6 � � �� ⟹ � � � � � �� � � (6) where V is the external volume of the cylinder and ̅ is the maximum strain considered. The specific energy absorption is obtained by normalizing with respect to volume. The stress was calculated considering the full cross sectional area of the cylinder, ��� � . The resulting values at 60% strain are summarized in Table 4. Table 4. Specific energy absorption (SEA) at 60% strain.

���������� ( J/cm 3 ) ���������� ( J/cm 3 ) 3.9 28.8

Specimen

1 2 3

4.1 3.8

29.3 34.5