Issue 49

A. Bendada et alii, Frattura ed Integrità Strutturale, 49 (2019) 655-665; DOI: 10.3221/IGF-ESIS.49.59 660 nodes and 2592 elements. Geometric dimensions of the panel are shown in Tab. 8. The skins and the core are made of an aluminum alloy (Tab. 2). Table 8 : Geometric dimensions of the panel. Figure 3 : Numerical model of honeycomb sandwich panel. E XPERIMENTAL VALIDATION he non-destructive testing (NDT) is crucially important for composite structures during manufacturing, as well as in-service maintenance and repair and it play a fundamental role in the characterization of composite materials [19-21]. In this study, For the experimental modal procedure, the honeycomb sandwich plate surface is marked by 5 5  parallel grid points with the size of each element is 62.5 52.5 mm mm  . To avoid the boundary effects and presence of any other errors in free-free boundary condition experimental study, the structure is vertically suspended by flexible strings. Fig. 4 shows the modal testing setup which is executed by exciting all marked points of the panel using a PCB086C03 impulse hammer whose sensitivity is 2.25 mV. Consequently, a PCB356A15 accelerometer is fixed inside the structure at marked point number 1. A frequency response analyzer, NATIONAL INSTRUMENTS (NI) cDAQ-9184 executed the signal acquisition and conditioning. Finally, the frequency response functions (FRF) measurements (Fig.5) and associated mode shape are obtained. Figure 4 : Experimental set-up. Figure 5 : FRF measurements at 25 different grid points. Frequency - Hz Am plitude g/N 500 2k 1.5k 1k 0 80 60 40 20 Length ( mm ) Width ( mm ) Thick ( mm ) Core 250 210 8.8 Skin 250 210 0.6 T