Abstract: Because of its high strength-weight ratio and modulus-weight ratio, excellent thermal insulation performance,the foam sandwich composite has been widely used in aerospace industry. On airplane, it′s applied to some structures which are thin in thickness and bear small loads. Due to its particularity in material, the stress conditions of NACA carbon fiber reinforced composite air inlet with foam sandwich structure is rather complex under combined loads. As a result, there are few studies on the strength analysis of this kind of NACA air inlet so far. In this paper, the NACA composite air inlet with foam sandwich structure was selected as the study subject, and its finite element modeling was built. By analyzing and comparing the equivalent stress contours of the air inlet′s shell in different cases, along with checking the strength in stress concentration areas of the sandwich structure′s each layer, failures of foam core and composite skins were examined, and regularities about influences of loads on the air inlet were figured out. The results indicate that the stress concentrated areas of the composite layer are near the bolt holes, and for the foam layer they are near the joint regions between valve plates and shell of the air inlet. And, based on the results of finite element calculation, the foam would be destroyed under some extreme working-conditions. So foam with better properties should be adopted or stress concentrated areas of the foam layer should be reinforced.

Key words: foam sandwich, NACA, composite, air inlet, finite element analysis