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Experimental Approach to Investigate Facesheet Delamination of Honeycomb Sandwich Panels Under Ground-Air-Ground (GAG) Pressurization

Sandwich structures can exhibit several failure modes, depending on specific configuration of the structure as well as details of the applied load. One failure mode is delamination of the face sheet(s) from the core when subjected to Ground-Air-Ground (GAG) pressure cycles. The pressure differential develops with each ascent/descent cycle, causing mechanical stress and potentially face sheet delamination. The likelihood of delamination is increased if any defect(s) exists in the bondline between face sheet and core. In this study, the GAG cycle was recreated in a controlled laboratory environment. Three panels consisting of Nomex honeycomb core and 3ply, 4ply and 8ply face sheets were investigated. It was seen that the bulge created due to pressure differential in the 3ply facesheet was higher compared to 8ply facesheet. The out-ofplane displacement measured by Digital Image Correlation (DIC) for 3ply, 4ply and 8ply face sheets ranged between 0.42-2.46 mm. Moreover, fatigue analysis was performed on the three face sheets upto 50th GAG cycles which showed that there was slight increase in delaminations for the three face sheets after higher number of cycles. This test method proved to be an efficient way to predict delamination growth in sandwich panels when subjected to GAG pressurization cycles