Development of Sandwich Structures with “through-the-thickness” Composite Inserts

N K Naik, Department of Aerospace Engineering


'Sandwich' structures are widely used in the aerospace industry where weight is an important consideration. The basic purpose of a sandwich construction is to produce a stiff, strong and light weight structure. This can be achieved by combining a low density core with high stiffness and high strength face-plates. A sandwich structure is made of thick honeycomb / foam light weight core material and high strength aluminum / polymer matrix composite face-plates. The face-plates and core of the sandwich structure are bonded together with adhesive film.

         Generally, the core materials have lower density, in-plane elastic modulus and in-plane shear modulus. However, the face-plates have higher values of stiffness and strength. The face-plates carry bending load whereas the core carries shear load. The elastic modulus of the face-plates is two to three orders more than the elastic modulus of the core material. For high performance applications, usually the honeycomb structure forms the core as they have higher values of strength-to-density ratio.

         However, such structures are not strong enough to withstand the localized external loads as the in-plane normal and shear strengths of the honeycomb core materials are very low. If such structures need to absorb localized external loads, it is necessary to adopt special means in order to prevent the occurrence of premature failures induced by the local bending effects. One way of reducing such bending effects is the use of inserts......more on next page