Estimation of local sandwich panel indentation

The present paper deals with analysis of local indentation and their energies in point loading of sandwich panel with thin orthotropic composite skins and honeycomb core as an introduction for low velocity impact loading and energy absorbing in sandwich structures. The orthotropic model, which was used for composite skin, allows applying the estimation for mechanical behavior of isotropic metal sandwich panels. Energy is consumed in two stages: local indentation of sandwich panel skin and bending of sandwich pa¬nel. If the impact is located near support or clamping only first stage (indentation of sandwich panel) will be presented. Here the analytical model has been used assuming a rigid-perfectly plastic compressive behaviour of the honeycomb core and membrane elastic behaviour of orthotropic skin for large indentation of sandwich panel. The simplification of the real skin deformed shape with a piecewise linear surface in the local zone of indention allows to derive quite simple formulas to estimate contact behaviors and strength of panel even for large indentation. Indention tests of two types of sandwich panels carried out to verify the analytical model. The skin in the first case was made from unidirectional CFRP lamina with lay-up sequence [45/-45]s; in the second case - from aramid woven plastic (lay-up sequence [0/90]). The both structures had honeycomb cores, which consisted of impregnated paper like Nomex or one layer of glass fabric reinforced plastic. The length of a cell was equal to 2.5 mm. Tests were performed with INSTRON 5882 (static testing machine) with using contact extensometer and software Bluehill2. Required mechanical properties of skins were obtained from tension tests of specimens clipped from sandwich-panels. The experimental results are in good agreement with the analysis. These results can be used in impact loading and energy absorption studies of laminated structures by integrating of “local load vs deflection” curve.