A generalization of the refined zigzag theory (RZT) for the analysis of partially delaminated sandwich beams

This work introduces an extension of the refined zigzag theory (RZT) for the analysis of partially delaminated beams. The primary objective is to propose an enrichment of the kinematics that enables adequate modeling of beams composed of two external rigid layers and a flexible core (sandwich) in which partial delamination has occurred between the core and one of the external rigid layers. The extension of the RZT involves an improvement in the interpolation of axial displacements in the core through the addition of three degrees of freedom. These include the displacement jump that appears in the delaminated layer, as well as two additional variables associated with the curvature of the section in the core and the concentration of displacements in the delaminated area. The original RZT has a limitation in the treatment of non-homogeneous beams, specifically when the mechanical properties of the layers change along the length of the beam (as occurs in partial delamination), leading to a non-conforming approximation. The model proposed in this article is conforming and allows for a highly efficient approximation of the overall behavior of sandwich beams, including their stiffness characteristics and the discontinuity in the delaminated layer, while also improving the prediction of transverse shear stresses. Two examples are presented and discussed to demonstrate the effectiveness of the proposed approach.