Finite elements for honeycomb sandwich plates and shells

Abstract

The honeycomb sandwich type of construction in plate and shell shapes is playing an increasing role in aerospace structures where structural efficiency is important. In some applications, such as wing or control surface trailing edges, the core is of non-constant thickness, and in others, such as engine thrust reverser buckets, the shell shape is doubly curved. Faceplates are commonly manufactured from aluminium, stainless steel or other metals, but the use of anisotropic materials, such as carbon fibre reinforced plastics (CFRP) can be expected to increase in the future.In finite element analysis, as in analytical work, sandwich plates and shells have received far less attention than thin plates and shells. However, elements have been developed specifically for sandwich plates by Barnard, Cook and Bartelds and Ottens. Of these, only the latter allows a non-constant core thickness. Evidently, such elements could be used in a facet shell representation. Only two general (as opposed to axisymmetric) curved elements specifically formulated to deal with sandwich shells seem to have appeared in the literature. Both are subject to deficiencies as noted for thin shells by Morris, and Webber discusses certain geometrical errors in the doubly curved element of Reference 5. Furthermore, both are of limited practical application. It may be concluded, therefore, that there is a need for a honeycomb sandwich shell element which is easy to use and accurate while being capable of modelling the full range of materials and shapes found in practical structures. To this end, a family of elements for use in the linear elastic finite element method is formulated. They are of general doubly curved shape and can be used to approximate thick and thin shells of positive, zero and negative Gaussian curvature in a simple and straightforward manner. They also include anisotropic faces and non-constant core thickness. Degrees of freedom are limited to three displacements at each node, and this allows mixing with other element types.