Issue 49

A. Bendada et alii, Frattura ed Integrità Strutturale, 49 (2019) 655-665; DOI: 10.3221/IGF-ESIS.49.59 662 Mode order Experimental results (Hz) Numerical results (Hz) Error % 1 680.82 712.29 4.60 2 1081.42 1095.30 1.20 3 1393.90 1506.00 8.00 4 1511.35 1526.10 0.97 5 1638.42 1747.30 6.64 Table 10 : Comparison between experimental and numerical results for simple thickness wall. It can be observed from Tab. 9 that the mode shapes measured by experimental and numerical modal analysis are very much alike from the visual inspection, Comparison between frequencies is shown in Tab. 10, the maximum error is 8.00 %, and the mean error is 4.28%, results show that the equivalent elastic properties are not so efficient for reflecting the macro-mechanical parameters of the honeycomb core, this discrepancy can be explained by the neglect of the double thickness wall existing in aluminum honeycomb core (Fig. 6) in the analytical and numerical homogenization procedure. Figure 6 : Double thickness wall location. P RECISE CONSTANT PARAMETERS n this step, we have modified the program by introducing the double thickness wall (Fig. 7) to recalculate z E , xy G , yz G which influenced the results [14]. Tab. 11 represents the improved elastic parameters. z E ( MPa ) 796.196 xy G ( MPa ) -2 1.169 10  yz G ( MPa ) 88.81 Figure 7 : RVE with double wall. Table 11 : Improved parameters. Comparison between experimental frequencies and new identified results is presented in Tab. 12. The maximum error is no more than 4.5%, results show that the improved orthotropic elastic properties determined on taking into account the double cell wall are appropriate. Mode order Experimental results (Hz) New numerical results (Hz) Error % 1 680.82 702.04 3.2 2 1081.42 1091.20 0.9 3 1393.90 1456.70 4.5 4 1511.35 1497.50 0.9 5 1638.42 1692.00 3.2 Table 12 : Comparison between experimental modal frequencies and new computational results. I