Mid Sweden University

A simple analytical model for calculating the nonlinear deformations of a corrugated core (fluting) during out-of-plane compression is developed. The results from the analytical model are compared to a more comprehensive finite-element model and to experiments. A connection between the boundary conditions and the damage state of the corrugated board is discussed. Including a modified set of boundary conditions gives an almost perfect match of the initial stiffness to the experimental results, indicating that the core might be significantly damaged as a result of the manufacturing process. Possibly, the strength of corrugated boards might be increased about 20% if one could avoid damaging the fluting during the manufacturing process.

Because of the high computational cost involved when modeling a corrugated panel (in e.g., finite element analyses) the corrugated core sandwich is in this investigation homogenized and the panel is transformed to an equivalent continuous homogenous layer with effective equal properties. Mathematically, the corrugated board panel is divided into an arbitrary number of thin virtual layers. For each virtual layer, unique effective elastic modules are calculated. Then, the elastic properties in all layers are assembled together in order to be able to analyze a corrugated board as a continuous structure having equivalent mechanical properties to a real structure. It is shown that by using shear correction factors derived from an equilibrium stress field, improvements in the calculated stiffness and deflections can be achieved in circumstances when a corrugated board panel is subjected to bending. Following the algorithm outlined, the shear correction factors are easy to calculate and become a valuable tool when performing mechanical analyses of corrugated boards. The capability of the model to properly capture and simulate the mechanical behavior of corrugated boards subjected to plate bending as well as three-point-bending has been demonstrated by means of several numerical examples, which are compared to experiments on corrugated board panels of varying geometry.