The effect of thickness on the transverse shear strength of nomex honeycomb cores

Honeycomb materials are commonly used as cores for sandwich panels. While empirical evidence exists showing that the transverse shear strength of a honeycomb core is affected by its thickness, the accuracy of empirical guidelines and the reasons for the changes in strength are not well understood. Four-point flexural testing of sandwich beams and a detailed cellular finite element model are used to investigate transverse shear failure of Nomex (TM) honeycomb core material. Transverse shear strengths at varying core thicknesses were compared to manufacturer specifications and used to determine normalised strength correction factors for thickness. These factors correlated well with trends shown in previous literature, where core shear strength decreases with increasing core thickness. The failure mode investigation showed a transition between modes as core thickness increased. The thinner cores experience shear fracturing of individual cell walls followed by local cell wall buckling, intermediate thickness cores initially failed by cell wall local buckling, then fractured and larger thickness cores appeared to fail by overall cell column buckling.