Micro- and meso-instabilities in structured materials and sandwich structures

The reason for the onset of undesirable nonlinear mechanical behaviour of structures can often be found in instability phenomena on length scales that are much smaller than those of the component. Micro-buckling in cellular materials, e.g., may lead to layer-wise collapse of the cell structure, corresponding to a characteristic plateau in the overall compressive force-displacement relationship. Correspondingly, local buckling of the face sheets or the cores of sandwich plates may mark the onset of buckling of the whole sandwich plate. To account for the importance of understanding and predicting of buckling on small length scales this paper discusses buckling phenomena in open and closed-cell cellular materials as well as in sandwich structures with unstructured and structured cores. Analytical and numerical methods for predicting corresponding critical loads are presented. Most of these methods rely on the assumption of an actual, or representative, periodic micro-structure for facilitating the analysis. The influence of boundary conditions and some localisation phenomena are also discussed.