These structures offer an exceptional benefit when they are used in aeronautics, the incorporation of this technology into the aircraft structures has proved to be a great solution for mass reduction problems due to their important bending stiffness and low weight, which allows to design lightweight parts.
When a load is applied to these panels, the core absorb almost all the shear component of the force, therefore the shear properties of the core are indispensable for the sandwich design.
In aeronautics, it is very common to use Nomex or aluminum honeycomb cores. In this work we will show an analysis of the shear nonlinear behavior of three of them. Forty four test are conducted for this purpose on the Nomex core HRH-78, HRH-10 and aluminum 5052 3/8 and also using different types design for the test specimens.
Initially a benchmark of four different type of specimens was made: a three point beam classic design, a single rail design, a double rail design, and a two materials double rail design. We decided that the double rail design was the best option for our tests.
It is well known that the hexagonal geometry of the honeycomb cell causes different mechanical properties according to the cell direction, L or W and we have analyzed the nonlinear behavior in both of them.
Additionally, two kinds of test are be performed, a static test to determine the overall nonlinear response and a cyclic test to analyze the effect of shear buckles on the strength of the honeycomb.
This gives a total of 12 different tests conditions (3 types of honeycombs x 2 directions x2 types of tests). However to get reliable results and to check the reproducibility of the obtained data, we have made 3 times every test, resulting in a total of 36 tests.
To better understand the failure scenario of the core due to the buckling of the cells, a 3D image correlation system was used to record the experiments and later to create a virtual surface of the exterior of the material. A detailed analysis of the pattern of the bucked cells was made using an artificial neuronal network.
Then a 3D model of the cores was created using ABAQUS/standard to compare the experimental data versus an equivalent numerical simulation, this is very useful to better understand the nonlinear behavior of these types of structures and several authors are interested .
Finally a simplified approach for the Nomex honeycomb core is proposed for macro-scale simulation.
This work aims to contribute on the analysis of inserts in sandwich structures where the Nomex honeycomb core properties are very important for the embodiment design .
REFERENCES  R. Seemann and D. Krause, “Numerical Modeling of Nomex Honeycomb Sandwich Cores at Meso-Scale Level,” Compos. Struct., 2016.
 P. Bunyawanichakul, B. Castanié, and J.-J. Barrau, “Non-linear finite element analysis of inserts in composite sandwich structures,” Compos. Part B Eng., vol. 39, no. 7–8, pp. 1077–1092, Oct. 2008.