Out of plane elastic compressive properties of metallic honeycomb structures

This research work assesses the influence of three geometric factors on the off-plans compression module of metallic bee nest structures, specifically in aluminum: cellular topology, the height of the alveolar structure and the geometry of the sample. The objective is to verify whether the typical modules values ​​provided by manufacturers, often supposed to be constant, remain valid under different configurations.

Historically, theoretical models (notably from Gibson & Ashby) offer a formula connecting this module to the relative density and to the Young module of the material. However, significant differences are observed between theoretical and experimental modules, especially for low density bee nests. This is explained by micro-defects such as micro-perforations and micro-flashes of the walls, as well as by the overestimation of Young modules for very fine materials.

To investigate these phenomena, compression tests according to the ASTM C365 standard were carried out, as well as finite element models (FEM). The tests show that cellular topology strongly influences mechanical performance: a modified geometry with corrugated walls significantly increases the compression module (up to 118% for only 7.9% volume mass increase) compared to a conventional hexagonal structure.

In addition, the height of the honeycomb (absent parameter of theoretical formulas) also has a notable impact. Tests on heights of 5 mm, 10 mm, 15.9 mm and 44 mm reveal that the compression module grows with the increase in height, also reducing the elastic deformation area. For low heights, the adhesive used in stabilized compression tests seems to influence the results. 

Digital simulations reproduce these experimental trends well, highlighting two elastic regimes: a first theoretical regime followed by a second diet dominated by micro-flashes. This digital approach confirms that mechanical performance does not depend only on the material and the density, but also on the geometry of the cells and the height of the soul material.

In conclusion, this study demonstrates that the off-plan compression module of metallic honeycomb nests is not a universal constant. It strongly depends on the geometric characteristics of the cellular network, which calls into question the often used simplifying generalizations. The integration of these factors is essential for applications requiring high mechanical precision, especially in aeronautics and space.