Indentation law for lightweight sandwich plates

Sandwich structures consisting of high-modulus thin skins and a low-modulus thick core are sensitive to local loading, which causes local indentation. Classical approaches determine the deflection of sandwich structures by a superposition method where the local compression of the core for a panel on a rigid foundation is added to global sandwich bending without core compression. In this article, a sandwich plate is analyzed using a higher-order sandwich panel theory (HOSPT) where the faces are modelled by classical laminate theory and the core by a three-dimensional elasticity solution. The results are obtained from 14 partial differential equations for displacements of the faces and core. HOSPT determines core compression with a second-order distribution of displacement through the core thickness. The force versus core compression relations in the fully backed and clamped states are compared and it is shown that the core compression assumed in the classical approach differs from the core compression in a clamped state. Results are verified by ANSYS® FEM software and experimental data. A few sandwich panel specimens were made with glass reinforced plastic (GRP) skins and a polyurethane foam core. Results from indentation tests on the panels are compared with finite element, HOSPT, and other theories.