Analysis of debonding fracture in a sandwich plate with hexagonal core

In lightweight applications (as, e.g., aerospace structures) sandwich constructions are very useful and common due to their superior specific bending stiffness and bending strength. In many cases the sandwich consists of an upper and lower laminate facesheet and an intermediate hexagonal cellular aluminum core. Along their interfaces the facesheets and the core are glued together. In order to ensure structural integrity, the facesheet/core bonding is of particular interest. Finite element method has been used to study the cause and the effects of debonding phenomena in between the facesheet and the core of a sandwich plate under inplane loading. A "unit cell" approach has been followed throughout the study. It has been observed that under an applied in-plane loading, there is a significant stress concentration at the junction of three cell walls and facesheet which easily leads to the generation of cracks and their growth. In order to judge about the tendency of crack initiation and growth, hypothetical interface cracks have been considered and analyzed by fracture mechanics technique. In doing so for various crack length, the energy release rate has been calculated and assessed by means of Irwin's crack closure integral for a number of different situations. It has been observed that there is a significant amount of energy release rate even in the case of a very small or virtually no crack. This phenomenon indicates that the glue used to attach the facesheet and the cell must withstand a non-zero energy release rate even in the intact situation without any debonding. (C) 2000 Elsevier Science Ltd. All rights reserved.