Indentation failure analysis of sandwich beams

Failure of sandwich honeycomb structures under indentation loading is considered. A failure criterion for Nomex honeycombs subjected to combined compressive and shear stresses is determined using biaxial tests. By combining this with a theoretical calculation of the stress distribution in the core due to indentation loading, found from a high-order sandwich beam theory (HOSBT), the indentation Failure load of the sandwich beam due to core failure can be predicted. It is assumed that both the skin and core are elastic up to Failure, which is a reasonable approximation for the GFRP skins and Nomex cores considered. Short beam 3-point bending tests are used to validate the theoretical predictions, using beams made with GFRP skins and Nomex cores with densities between 29 and 128 kg/m(3). Theoretical predictions of indentation failure load are in excellent agreement with measured values. Inclusion of shear stresses in the failure criterion significantly improves the predictions, correctly modelling the observed stronger behaviour of cores with a longitudinal ribbon direction. (C) 2000 Published by Elsevier Science Ltd.