Non-linear behavior of a face-sheet debonded sandwich panel – Thermal effects

Abstract

Geometrical non-linear analyses of a sandwich panel with a prescribed debond within one of the face sheets where the core is either incompressible (stiff) or compressible (compliant) are presented. A loading scheme of thermal or mechanical loads independently or combined thermo-mechanical load is considered. The debond, in one of the face sheets, consists of a through-the-width crack that divides it into two layers, one with a free surface (upper or lower) and the other attached to the core. The interfaces of the debonded crack are free of shear stresses but can only accommodate vertical normal compressive stresses. In the case of a compliant core the high-order sandwich panel (HSAPT) model is adopted and in case of an incompressible core the ordinary beam theory (OBT) and the first-order shear deformable theory (FOSDT) (equivalent single layer, ESL) are used. The mathematical formulation outlines the field equations along with the stress and displacements fields for the cases where the core (stiff or compliant) properties are either temperature independent (TI) or dependent (TD). The governing equations along with the appropriate boundary and continuity conditions are derived using variational principles following the principles of the HSAPT or ESL models. The non-linear analysis includes geometrical non-linearities in the face sheets caused by rotation of the face cross sections and high-order effects that are the result of the compliant core. The core stress and displacements fields with temperature-dependent (TD) mechanical properties are determined in a closed form using properties that are vertically coordinate dependent. The numerical study looks into the effect of the thickness (thin, moderate and very thick) of the debonded layer that is not attached to the core in the presence of mechanical and thermal loads on the non-linear response. An inner delamination is considered, around mid-span, for specific lengths with TI or TD mechanical properties. The results reveal that the ESL models cannot be used to predict the non-linear response of a sandwich panel with a compliant core. In addition, the existence of a debond crack nearby the face–core interface (very thick layer) may be associated with local buckling of the thin layer that is bonded to the core.