Failure analysis in pure bending of single-face honeycomb core sandwich beams

This study is focused on failure of single-face honeycomb core sandwich beams loaded in four-point flexure. The beams are configured for pure moment loading of a single-face sandwich (SFS) where the lower region of the core is under compression. Failure of the beam is assumed to occur when the maximum compressive strain in the core reaches its ultimate value in uniaxial compression. Analysis of the stiffness and failure load of the beam utilizes laminate beam theory. Constraint on the dominant bending deformation of core cell walls develop in honeycomb core sandwich structures because the cell walls are adhesively bonded to rigid face sheets. This constraint elevates the effective extensional modulus of the core. This effect is incorporated in the analysis by replacing part of the core with a gradient layer. Single-face sandwich beam specimens consisting of carbon/epoxy face sheets and Nomex honeycomb core were tested in flexure. Experiments and analysis demonstrate that the one-sided constraint on the core significantly increase the bending stiffness and bending strength of the single face sandwich beams. For a typical SFS specimen, it is shown that the constraint elevates the stiffness and strength by 13 and 16%, respectively. The gradient core model predictions of the failure load of the single-face specimens are in good agreement with experiments.