High-order bending analysis of unidirectional curved "soft" sandwich panels with disbonds and slipping layers

The bending behavior of unidirectional singly curved sandwich panels with a "soft" core and delaminated (debonded) zones or slipping layers is described herein. The delaminated zone is assumed to exist through the width of the panels, and is in the form of an interfacial debonded zone at one of the face-core interfaces, thus subdividing the length of the panel into three zones, i.e. two fully bonded zones and one that is debonded (delaminated). The formulation uses an interfacial spring description, i.e. distributed shear and radial normal springs at the face-core interfaces, to model the effects of the slipping layers and the various delaminated (debonded) zones. The formulation is based on a closed-form high-order approach (HSAPT) that incorporates the high-order effects of the "soft" core. The variational approach is used to derive the governing equations along with the general explicit boundary and continuity conditions. A typical curved sandwich panel with an inner or an edge delamination, with or without contact, subjected to a distributed load and pinned supports is discussed. A comparison between the various delamination types and the fully bonded case is presented in terms of the displacements, stresses and internal stress resultants of the faces and in the vicinity of the edges of the delaminated zones. Finally, the effect of slipping interfacial layers, with or without contact when subjected to a distributed load, is considered and compared with the behavior of a fully bonded sandwich panel. From the numerical studies it is found that the membrane action of the face sheets plays a major role in the overall structural resistance of the sandwich panel compared to that of flat panels. However, in the near vicinity of the edges of the debonded zone, the membrane action does not prevent the interfacial stresses to reach very large values in the case of delamination without contact. For all of the delamination types, contact exerts a favorable effect, in the sense that the induced interfacial stresses are much smaller when compared to cases of delamination without contact.