Issue 36

J. Kováčik et alii, Frattura ed Integrità Strutturale, 36 (2016) 55-62; DOI: 10.3221/IGF-ESIS.36.06 57 where  CS0 is the compression strength of the solid material without porosity;  is the density of foam;  0 is the density of solid material;  /  0 is the volume fraction of metal. The fitting of the experimental results to Eq. (2) showed that the scaling exponent T f is in the range of 1.89 – 2 depending on alloy composition, sample size and surface skin presence (see Tab. 1 and Figs. 2 and 3). The results indicate that it is a universal critical exponent: it is independent on the compression mechanisms of the cell-walls and is almost the same for both brittle compression of casting aluminium alloy AlSi11Mg0.6 (see Fig. 1.a) and plastic deformation of wrought aluminium alloys Al 99.96 and AlMg1Si0.6 (see Fig. 1.b). The lowest values of T f were obtained for the samples with surface skin, because the skin oriented parallel to the applied load increases the sample strength at constant volume fraction of metal. It must be further noted, that the data for the compression strength of metallic foams showed statistical fluctuations due to various pore sizes, shapes and orientations at constant porosity (see Fig. 4). Figure 1 : Typical stress-strain curves for, the definition of the compression strength of and the macroscopic structural changes at compression strength for: (a) brittle AlSi11Mg0.6 foam, 0.18 volume fraction of metal, (b) ductile Al 99.96 foam, 0.31 volume fraction of metal. Matrix alloy Geometry [mm] Range of volum fraction  CS0 [MPa] T f [ - ]  2 [ - ] N [ - ]  20 x 25 0.09 - 0.44 69.8±2.6 1.96±0.11 6.67 16 Al 99.96  28 x 32 (skin) 0.18 - 0.41 69.9±0.8 1.94±0.04 0.65 8  40 x 51 (skin) 0.17 - 0.32 70.0±0.8 1.89±0.04 0.68 12 AlMg1Si0.6  20 x (10-40) 0.07 - 0.40 114.9±1.5 1.97±0.03 2.20 65 AlSi11Mg0.6  20 x (10-40) 0.10 - 0.89 305.0±4.1 2.00±0.04 40.0 77 Table 1 : Composition, sample geometry and observed scaling exponents for investigated metal foams determined via Eq. (2).  2 is the error of the fitting. N is the number of measured foam samples used for fitting.