Issue 53

Y. Saadallah, Frattura ed Integrità Strutturale, 53(2020) 417-425; DOI: 10.3221/IGF-ESIS.53.32 423 other three depend on it weakly. This low dependence probably results from the small difference in the densities of the samples. It would therefore be interesting to plan other studies with samples of remarkably different densities. Density (g/cm 3 ) 0.2340 0.2477 0.2534 A (MPa) 5.10 -5 5.10 -5 5.10 -5 B (MPa) 0.0044 0.0049 0.0045 C (MPa) 0.1583 0.1722 0.1456 K (MPa) 0.0234 0.0445 0.0641 Table 2: Nonlinear model parameters by density. Fig. 7 establishes a test-model comparison between stress-strain curves of cork in compression in a non-radial direction. There is a very good consistency of the results with the nonlinear model in the three domains, but even better in the densification domain. In contrast to the case of the tri-linear model, there is a minimum difference in the densest sample. By deriving the polynomial of the loading with respect to the strain in the case of the nonlinear model, we obtain the loading derivative. Fig. 8 shows us that this derivative decreases up to 30% of deformation where it reaches its minimum value. This minimum can be considered as another parameter of the cork from which the material hardens and thus the loading derivative increases until the end of the test. (a) (b)