Study On Mechanical And Dielectric Properties Of Honeycomb Core Materials

Honeycomb core materials are widely used in aircrafts for their lightweight character, good mechanical and electromagnetic properties. Mechanical and dielectric properties of irregular honeycombs are investigated in this thesis, and the influence on mechanical (effective elastic parameters) and electromagnetic properties (effective permittivity) of honeycomb governed by the geometric parameters of unit cell layout is obtained. Contributions in this thesis are listed as follow:(1) By considering of bending, shear and uniaxial deformations of honeycomb cell wall, new formulas of equivalent elastic parameters of infinite wide and finite honeycomb core are created based on Bernoulli-Euler beam model. Compared to Gibson formulas, equivalent elastic parameters calculated from formulas presented in this thesis are much closer to the compressing experiments data.(2) By using of orthogonal experimental design and finite element method (shell element), an artificial neural network is created to simulate the nonlinear mapping between four main factors and equivalent elastic parameters of honeycomb core, and BP neural network method is adopted to predict those parameters of finite width honeycomb core.(3) To overcome the drawback of in-plane equivalent elastic modulus of infinite wide honeycomb core in Gibson formulas, homogenization method is introduced to build the relationships between equivalent elastic parameters and geometry of the irregular unit cell. Based on the asymptotic expansion, the effect of geometry of unit cell on elastic properties of honeycomb core is solved by finite element method.(4) By using of Finite element method for high-frequency electromagnetic field, the reflection coefficient and input impedance is predicted of an infinite planar layer of dielectric honeycomb subject to illumination from three mutually orthogonal directions. The reflection data are inverted to obtain data on the honeycomb's effective permittivity based on a conventional plan wave transmission line model of the honeycomb.(5) Finally, the multi-objective optimization for effective elastic parameters and effective permittivity of honeycomb core has been investigated by using NCGA (Neighborhood Cultivation Genetic Algorithm) of iSIGHT optimization software.