Single and double-layer honeycomb sandwich panels under impact loading

Honeycomb sandwich structures have excellent energy absorption capabilities, combined with good mechanical properties and low density. These characteristics make them ideal for the transportation industry, which has a growing interest in reaching higher safety standards. The purpose of the present paper is the introduction of lightweight and more efficient crashworthy structures. Double-layer honeycomb sandwich structures were analysed and their energy absorption capabilities were evaluated by means of low-velocity impact tests. The specific energy absorption of double-layer panels was compared to single-layer honeycomb and other lightweight panels, in order to assess the effectiveness and the convenience of the introduced solution for lightweight and crashworthy devices. The impact absorption mechanism was evaluated through Computed Tomography images and visual inspection. A theoretical evaluation was applied to investigate the mono-layer impact response. The results were compared to those obtained with different boundary conditions and with a full-scale test. Contact parameters were influenced by boundary conditions since they depend on the specimens stiffness. Double-layer panels displayed a progressive collapse sequence, depending on the core arrangement and on the cell size. Honeycomb with larger cell size showed a better distribution of the impact loading which generated an almost uniform compression of the core. Such observations suggested the possibility to obtain energy absorber devices with a controlled deformation. Preliminary considerations on the existence of a size effect were drawn, since it was observed a relation among the contact parameters and the geometrical characteristics of the honeycomb and the indenter.