Effect of Using an Inner Plate between Two Faces of a Sandwich Structure in Resistance to Bird-Strike Impact

Because the total thickness of the sandwich structures in aerospace structures is a limit, one way to improve the mechanical resistance against bird strike can be inserting an inner plate inside the core without increasing the total thickness. In this study, the effect of inserting an inner plate and its positioning on the resistance of sandwich structure against bird strike is investigated by means of a finite-element code. Experimental results have been used for validation of the numerical model. Aluminum alloy 2024 and aluminum AlSi7Mg0.5 foams with different densities were used for the face sheets and the inner plate and foam cores, respectively. It was seen that in the cases with an inner plate, the optimum inner plate position is when it is inserted at the middle of the foam. This case improves the resistance of the sandwich structure with respect to the case with no inner plate. The inner plate is also very helpful when the densities of the foam cores are different at the two sides of inner plate, especially when the top foam core is low density and the bottom foam core is high density. This is due to the fact that the inner plate spreads the impact energy to a very large area of the bottom dense foam core, and therefore decreases the final deflection of the bottom face sheet to a great extent.