Elastic Foundation and Timoshenko Beam Theory Solution for Face/Core Sandwich Debonds

Abstract

This paper presents closed-form expressions for the energy release rate and mode partitioning of face/core debonds in sandwich composites with orthotropic faces and core, by use of an elastic foundation analysis. The elastic foundation analysis used here is comprehensive and includes the deformation of the substrate part (core and the bottom face) and is done for generally asymmetric sandwich construction. To capture the transverse shear effects, the Timoshenko beam theory is used, which introduces an additional degree of freedom. A finite length sandwich is treated as having a debonded section, where the debonded top face and the substrate are free, and a bonded section, where an elastic foundation is used between the face and the substrate. The interaction between the face and the substrate in the bonded section is modeled using both normal and shear spring distributions. A double-cantilever beam specimen with applied external moments and shearing forces is chosen to demonstrate the procedure. The energy release rate is obtained by use of the J-integral. A mode partitioning measure in terms of the crack flank opening and shearing displacements is used. The results are compared with finite element results and show very good agreement.