New structural form of sandwich core

Abstract

The purpose of this study is to present a new structural form of sandwich core. The observation, that the characteristics of honeycomb core is distinctly attributable to its stabilized perpendicular wall elements, leads to the possibility of a hypothetical core concept characterized by stabilized oblique wall elements. To embody the hypothetical concept, the core form constituted by superposing two mutually orthogonal corrugations is proposed. The resultant core can be manufactured from a single sheet by some press forming technique. The theoretical and experimental analyses of the core reveal that the shear modulus and strength are comparable with those of honeycomb core, and the elastic properties can be designed to be either isotropic or orthotropic. Other features of the core such as the simplicity of form, the applicability to both flat and curved sandwiches, and the possibility of circulating fluid between facings, may excite new applications of sandwich construction in aircraft structures. Nomenclature a — area of rhomboidal element E = Young's modulus g, h = periodic functions G = shear modulus l,m,n = components of unit normal vector r = unit vector t = uniform thickness of rhomboidal element U = strain energy v = gross volume between facings filled by a fundamental region x,y,z = rectangular Cartesian coordinates ot = filling factor of core 0 = reduction ratio [seeEq. (8)] 7 = shear strain e = normal strain 0 = inclination angle of oblique element fi = form efficiency of core [ see Eq. (7) ] a = normal stress v — Poisson's ratio r = shear stress i// = direction, \j/ radian counter-clockwise from .x-axis on x-y plane co = zigzag angle of ridge Superscript