Issue 48

O. A. Mocian et alii, Frattura ed Integrità Strutturale, 48 (2019) 230-241; DOI: 10.3221/IGF-ESIS.48.24 237 Damage assessment Impact damage assessment of the tested sandwich panels was carried out through visual inspection on the front and back facesheets of the panels. High resolution photographs were taken to assesS the damage extension for all adopted impact velocities. This images were used to measure the damaged areas in sandwich panels with composite facesheets using the ImageJ software [37], which is an open source image processing program designed for scientific multi-dimensional images. For panels with aluminum facesheets the indentation depth, defined as the residual depth of the depresion of the aluminum facesheet surface caused by the impactor during the impact event, was measured. Results are presented in Tab. 4 and Tab. 5. Facesheet perforation is marked with “  ”, while for sign “x” a no perforation situation appeared. Moreover, close up images of the central part of the impacted sandwich panels are presented in Fig. 5 and Fig. 6. Sandwich panel Damage area [mm 2 ] Facesheet perforation Top Bottom Top Bottom PUR PS PUR PS PUR PS PUR PS SPA_3 737.76 649.97 270.43 388.051   x x SPA_3.5 690.00 544.17 746.63 821.64   x  SPA_4 746.73 576.23 872.05 872.55     SPB_3 726.05 733.07 165.06 243.40   x x SPB_3.5 641.78 658.91 653.25 776.02   x x SPB_4 662.14 614.95 822.31 895.89     SPC_3 741.74 654.18 58.93 185.14 x  x x SPC_3.5 650.87 738.33 581.15 607.92   x x SPC_4 646.28 746.26 826.03 907.75    x Table 4 : Summary of damage events induced by impact loading in sandwich panels with composite facesheets. Sandwich panel Indentation depth [mm] Facesheet perforation Top Bottom PUR PS PUR PS PUR PS SPAl_3 8.23 13.38 x x x x SPAl_3.5 12.61 15.13  x x x SPAl_4 15.84 16.87  x x x Table 5 : Summary of damage events induced by impact loading in sandwich panels with aluminum facesheets. For the lowest impact velocity of 3 m/s, the upper facesheet of all sandwich panels with composite facesheets is perforated, irrespective of core type, except for the SPC_PUR panel, which is the most rigid one due to the PUR core and the composite facesheets with the highest amount of short glass fibers. The bottom facesheets present only matrix cracking, debonding and some fiber rupture, with no perforation (see Fig. 5). Composite sandwich panels with PUR foam core have a larger damage area on the upper facesheet and a smaller damage area on the bottom facesheet than those with PS foam core. The increased rigidity of the PUR foam reduces the absorption capability of the core and thus most of the impact energy is absorbed by the upper facesheet, which is more damaged. The sandwich panels with aluminum facesheets present a small indentation on the upper facesheet, with no perforation, and no visible damage on the bottom facesheet (see Fig. 5). By increasing the impact velocity to 3.5 m/s determines an important increase of the damage area in the bottom facesheets, almost 76% for PUR panels and 64 % for PS panels,while uppper facesheet perforation and debonding is almost the same for all composite sandwich panels. Moreover, the bottom facesheet of the less rigid composite sandwich panel, the SPA_PS panel, is perforated. The aluminum sandwich panels with PUR foam core, present local indentation and perforation of the