Estimation of out of plane shear moduli for honeycomb cores with modal FEA

Abstract

The main problem in analyzing honeycomb structures is the substantial computational effort that has to be spent in modelling and analyzing such a structure with a multi-cell construction core by maintaining the actual geometry. Therefore, the common practice in the finite element modelling of such structures is to replace them by an equivalent orthotropic material. The determination of these equivalent properties of the homogenized core are based on analytical or numerical relationships which are approximate. If the honeycomb core is part of a sandwich panel then the most important elastic constants for out-of plane loading are the out of plane shear moduli. This paper presents a numerical method that can be used to correct these two equivalent elastic properties of the homogenized material. Other elastic constants needed for bending and torsion loading are established relying on modal analyses applied for a real honeycomb panel, to obtain a reference solution, and then on the homogenized orthotropic sandwich panel where these equivalent elastic constants are iteratively improved by an optimization algorithm to fit the reference solution. The analyzed types of honeycomb cores in this paper are the commercial ones with three cell configurations: square, regular hexagonal and re-entrant shapes. The material of the core and the skin is aluminium. The in plane dimensions of the analyzed panels in modal analysis for equivalent properties determination are around 400 × 400 mm2 for two different thicknesses, 5 mm and 25 mm. The obtained results show that some of the equivalent elastic properties obtained in the classical way must be corrected as to obtain a proper response for bending and torsion loads.