Issue 30

T. Voiconi et alii, Frattura ed Integrità Strutturale, 30(2014) 101-108; DOI: 10.3221/IGF-ESIS.30.14 106 Necuron 100 145 300 651 Length, L [mm] 0.790 0.710 0.594 0.518 Inherent stress, σ 0 [MPa] 2.32 3.08 6.02 24.05 Table 4 : Summarized data for material constants L and σ 0 . An attempt to relate the material constants to the cell diameter and ultimate tensile stress of the cellular and porous materials was carried out. Fig. 5.a presents the variation of characteristic length L versus the cell diameter, and Fig. 6.b shows the plot of inherent stress with ultimate tensile stress. Both representations show a linear variation, and indicate an easy way to estimate the material constants (L and  0 ) based on material microstructure (cell diameter) and mechanical properties (ultimate tensile stress). y = 5.098x + 0.263 R² = 0.982 0.0 0.2 0.4 0.6 0.8 1.0 0.00 0.02 0.04 0.06 0.08 0.10 0.12 length L [mm] cell diameter [mm] y = 1.341x + 0.721 R² = 0.999 0 5 10 15 20 25 30 0 5 10 15 20 inherent stress  0 [MPa] ultimate tensile stress  u [MPa] Figure 5 . Influence of the relative density on material constants L and σ 0 . Validation of these material constants was performed on other notched geometry, respectively lateral U notches. Starting from the stress-distance curves obtained for an applied tensile stress equal cu 1 [MPa], the failure forces were predicted by simply rescaling these curves until the maximum principal stress σ 1 reaches the inherent stress  0 value at the critical distance L/2. The predictions, as can be seen in Fig. 6, are in agreement with the experimental results, the relative errors falling between ±15 [%], which represents a reasonable engineering approximation. 0 500 1000 1500 2000 2500 100 160 301 651 F max [N] Necuron Experimental results TCD prediction Figure 6 . Failure force predictions for U-notched specimens.