Experimental and numerical investigation of the effect of entrapped air on the mechanical response of Nomex honeycomb under flatwise compression

Nomex honeycomb has very low relative density, thus there is a lot of the air entrapped within the cells of Nomex honeycomb sandwich structures. The air has a significant effect on the mechanical response under flatwise compression, and it was investigated herein. Firstly, experiments of the honeycomb with and without facesheets were performed to study the entrapped air effect. Secondly, the unit cell model and multi-cell model of the honeycomb were proposed, in which, two methods of modeling the entrapped air using commercial software LS-DYNA were developed. In the first method, six cell walls and two facesheets as well as the air entrapped by them are simulated as an air-filled cavity using Airbag tools. In the second method, the entrapped air is simulated by ALE (Arbitrary Lagrangian Eulerian) elements, which realize the grid deformation and material flow. Interaction between the entrapped air and cell walls under compression is analyzed using fluid-structure coupling algorithm. It is found in this paper that energy absorption capacity of Nomex honeycomb sandwich can be enhanced through the effect of the entrapped air on the cell walls folding process. The ALE method is superior to the airbag method in the unit cell models as regard to the energy absorption capacity and the energy absorbing process.