Abstract
Sandwich construction incorporating a honeycomb cellular core offers the attainment of structures that are very stiff and strong in bending while the weight is kept at a minimum. Generally, an aluminum or Nomex honeycomb core is used in applications requiring sandwich construction with fiber-reinforced composite facesheets. However, the use of a fiber-reinforced composite core offers the potential for even lower weight, increased stiffness and strength, low thermal distortion compatible with that of the facesheets, the absence of galvanic corrosion and the ability to readily modify the core properties to suit specialized needs. Furthermore, the material of the core itself will exhibit anisotropic material properties in this case. In order to design, analyze and optimize these structures, knowledge of the effective mechanical properties of the core is essential. In this paper, the effective three-dimensional mechanical properties of a composite hexagonal cell core are determined using a numerical method based on a finite element analysis of a representative unit cell. In particular, the geometry of the simplest repeating unit of the core as well as the appropriate loading and boundary conditions that must be applied is presented.
Highlights
Sandwich structures can be used advantageously where low weight and high stiffness and strength are required, such as the traditional case in aerospace applications
The finite element model of the unit cell is simple, a difficulty normally found in this process is the determination of the appropriate boundary conditions that must be applied to the model in order to replicate the behavior of the overall core
As a result of its high stiffness and dimensional stability due to its hygrophobic nature, this material system is well suited for use in composite mirror applications
Summary
Sandwich structures can be used advantageously where low weight and high stiffness and strength are required, such as the traditional case in aerospace applications Composite materials, such as carbon fiber reinforced plastics (CFRP), are well suited for sandwich construction methods due to their low weight, high stiffness, high strength, dimensional stability, and ease of manufacture. Other non-traditional applications have emerged, such as in land and sea transportation [1] and in the construction of optical telescope composite mirrors [2,3] The latter requires very tight tolerances of dimensional stability and low weight, so a core made of CFRP material that is very stiff and at the same time has thermal expansion compatible with that of the facesheets can be used advantageously. In applications that require structural stability, such as composite mirrors, hexagonal cells offer the advantage of higher out-ofplane shear stiffness over triangular cells of the same density
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