In-plane compression modulus and strength of Nomex honeycomb cores

The stress-strain response and deformation mechanism of a range of Nomex honeycomb cores tested under in-plane compression has been examined experimentally. The cores with a thin wall displayed extensive bending deformation of the cell walls inclined to the horizontal (loading is vertical) and failed in bending. The cores with thicker walls failed by a shear-type instability of the cells indicated by tilting of vertical cell wall segments. The failure strain decreased with increasing core density. The modulus and compressive strength of the core were compared to micromechanical predictions. Normalized modulus and strength values varied between the various cores. The average modulus and strength results allow backing out of the modulus and bending strength of the Nomex paper. The results were in reasonable agreement with published tensile test results and composite micromechanics.