In the design, the main factors considered for the panel are the strength and stiffness of the material, and for the core material, the main factor considered is the maximum weight reduction. The core material in aircraft structures is usually aluminum honeycomb, foam or Cascell® honeycomb. Aluminum honeycombs or Cascell® honeycombs have the advantages of high compression modulus and light weight. They are widely used core materials for aircraft structures and are often used with carbon / glass fiber prepregs. Common structures include wing leading edge, rudder, landing gear hatch, wing body and wing tip fairing. Although the honeycomb sandwich structure has outstanding advantages over the metal sheet metal structure in terms of performance, airlines are still actively looking for alternative materials because the honeycomb sandwich material requires high maintenance and repair costs during use.
In some cases, if cracks and porosity occur in the panel, water and water vapor can easily enter the honeycomb. At low temperatures, the water entering the honeycomb pores will swell after being frozen, which will destroy the adhesion of adjacent honeycomb cells, which reduces the performance of the sandwich structure and must be repaired. The maintenance cost of the honeycomb sandwich component makes the original light-weight advantage no longer exist compared to the foam core structure. Since the rigid foam core is closed-cell, water and water vapor cannot enter the core, reducing the cost of maintenance and inspection Therefore, the full life cost of the foam sandwich structure is more economical, although the weight of the foam is slightly heavier than the honeycomb when the same shear capacity is reached.
With a series of problems in the use of composite honeycomb sandwich structures, researchers in the aerospace industry at home and abroad have turned their attention to high-performance polymer foam core materials, mainly PMI foam materials. In sandwich structural members, the use of a foam core can both reduce manufacturing costs and serve as a structural material. If only considered as a structural material, the design of the core foam structure and the honeycomb core sandwich structure are mainly at a disadvantage in terms of weight.