Non-uniform Compressive Strength of Debonded Sandwich Panels – II. Fracture Mechanics Investigation

Abstract

This article describes the development, validation and application of a FEM based numerical model for prediction of residual strength of damaged sandwich panels. The core of the theoretical method is a newly developed procedure for prediction of the propagation of a face-core debond. As demonstrated, the method can predict the maximum load carrying capacity of real-life panels with debond damages, where the failure is governed by face-sheet buckling followed by debond growth. The developed theoretical procedure is an extension of the as Crack Surface Displacement method, here denoted as the Crack Surface Displacement Extrapolation method. The method is first developed in 2D and then extended to 3D by use of a number of realistic assumptions for the considered configurations. Comparison of the theoretical predictions to a series of large-scale experiments, described in [17], shows that the model is indeed able to predict the failure modes and the residual strength of damaged panels with accuracy sufficient for practical applications. This opens up for a number of important engineering applications, for example risk-based inspection and repair schemes.

Damage Tolerance of Naval Sandwich Panels

“…The kinematics of the problem is geometrically nonlinear so that the stress intensity varies non-linearly with the applied load. This problem has been thoroughly investigated by Berggreen [30][31][32]. He studied sandwich panels with circular interface debonds subjected to various types of in-plane compression loading.…”

Failure investigation of debonded sandwich columns: An experimental and numerical study

“…Energy release rate (G) and phase angle (ψ) were determined from relative nodal pair displacements along the crack flanks obtained from the finite element analysis using the CSDE method outlined in [Berggreen and Simonsen 2005;Berggreen et al 2007]. The energy release rate and the phase angle are given by (see [Hutchinson and Suo 1992])…”

“…Energy release rate (given by the expression for G on page 1475) and mode-mixity are determined based on relative nodal pair displacements along the crack flanks obtained from the finite element analysis. The CSDE method [Berggreen and Simonsen 2005] and the mode-mixity formulation (expression for ψ K on on page 1475) were used.…”

“…The study showed that the compression strength reduction caused by a debond can be explained by two mechanisms: First from the interaction of local debond and global column buckling and secondly from the development of a damage zone at the debond crack tip. Only a few works have in detail assessed determination of fracture parameters like energy release rate, phase angle and debond propagation in composite and sandwich structures subjected to in-plane loading [Sallam and Simitses 1985;Avilés and Carlsson 2007;Nøkkentved et al 2005;Berggreen and Simonsen 2005]. The first of these papers presented a one dimensional model to estimate the delamination buckling load and ultimate load-carrying capacity of axially loaded composite plates, while the other three focused on sandwich panels containing two-dimensional embedded debonds.…”

Fracture Mechanics Analyses for Interface Crack Problems - A Review

“…Wang and Zhang [97] presented a new analytical solution for the energy release rate and the phase angle at an interface crack in a sandwich based on interface fracture mechanics solutions and composite beam theory. A promising method for the prediction of disbond propagation at the sandwich face sheet/core interface was suggested by Berggreen et al [98,99]. The CSDE method is based on the complex stress intensity factor K defined in equation (5) and the so-called Crack Surface Displacement technique proposed by Matos et al [100].…”