Materials Engineering Department
BS in Materials Engineering
The design process at Zodiac Aerospace requires the ability to accurately predict the strength of a composite honeycomb core sandwich panel to adhere to strict FAA regulations. The most common failure mode in long beam composites is in compression. Following ASTM D7249 for a four-point bend test of a long beam flexural test, a mechanical model has been developed that relates the compressive strength of glass fiber face sheets to the flexural strength of the sandwich panel. Zodiac does not currently have data on the compressive strength of the face sheets, so testing was performed to find this property. Asymmetric panels (n:n+1 plies) were designed to ensure a compressive failure in a four-point bend test. The compressive strength of the face sheets were found to be 26-42 ksi. To validate the model, testing on symmetric panels was performed in a full factorial design. Face sheet thickness, core direction and core thickness were variables tested within the panels. The failure loads increased significantly with higher face sheet thickness and core thickness, and are therefore important factors in the model. The study on core direction is inconclusive; however, there is reason to believe a difference exists between the two. Two correction factors regarding the core and fabric directions are added to modify the model. Some limitations of the model were also found, as a shear strength limit needs to be incorporated in a complete prediction of failure loads of the sandwich panels.