Discrimination between weak adhesion, delamination and kissing bond at the interfaces of composite bonded assemblies

Abstract

In this work, the impact of delamination, weak adhesion and kissing bond defects at the interfaces of trilayer composites structures, are numerically investigated in order to differentiate these three phenomena that are usually encountered in composite bonded assemblies. The structure is composed by two carbon-epoxy composites with 1.8 mm bonded by an adhesive epoxy of 0.5 mm. The Stiffness Matrix Method (SMM) is used to calculate the transmission and reflection coefficients of bulk waves likely to propagate in a trilayer structure immersed in water. Then, the behaviors of the symmetric and antisymmetric Lamb modes are analyzed. Four different states of interfaces are considered: (a) nominal interfaces with good adhesion, (b) interfaces with weak adhesion, (c) interfaces with delamination and (d) interfaces containing kissing bond defects. The carbon-epoxy composite is considered as an orthotropic layer and the epoxy adhesive interface as an isotropic layer. Results show that, only the antisymmetric Lamb modes are affected by the presence of kissing bond defects while the symmetric and antisymmetric Lamb modes are affected by the presence of delamination at the interfaces. In addition, weak adhesion only partially preserves the symmetric modes (with a shift in their frequencies) and introduces a reduction in amplitude compared to kissing bond like defect. The potential of the proposed method for the qualification of bonded composite structures is clearly demonstrated, with the ability to discriminate among three categories: weak adhesion, delamination and kissing-bond-like defect.