Experimental and Numerical Study of Interface Crack Propagation in Foam-cored Sandwich Beams

Abstract

This article deals with the prediction of debonding between core and face sheet in foam-cored sandwich structures. It describes the development, validation, and application of a FEM-based numerical model for the prediction of the propagation of debond damage. The structural mechanics is considered to be geometrically nonlinear while the local fracture mechanics problem is assumed to be linear. The presented numerical procedure for the local fracture mechanics is a further development of the crack surface displacement method, here denoted as the crack surface displacement extrapolation method. The considered application example is to tear off one of the face laminates from the sandwich. This configuration can be found in many applications but is considered here to be occurring in a ship structure, particularly at the hard spot where the superstructure meets the deck. Face tearing experiments are carried out for structures with three different core densities, material tests are carried out and finally the face tearing tests are simulated with the developed procedure. It is shown that for low core densities, where the crack propagates in the interface immediately below the face sheet, there is fair agreement between experiments and theory. For cores with higher density, the crack tends to propagate in the laminate itself with extensive fiber bridging leading to rather conservative numerical predictions. However, for structural configurations where LEFM can be applied, the presented procedure is sufficiently robust and accurate to be used in a number of important engineering applications, for example risk-based inspection and repair schemes.

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

“…A detailed kinking analysis, similar to what is presented in [Li and Carlsson 1999;Berggreen et al 2007], must be carried out to investigate this further. This is however out of the scope of this paper.…”

“…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])…”

“…For details, see [Berggreen et al 2007]. specimens as a result of the large bending and shear stiffnesses of the steel reinforced upper face sheet.…”

Interfacial Crack Arrest in Sandwich Panels with Embedded Crack Stoppers Subjected to Fatigue Loading

“…Several methods have been proposed based on the Finite Element Method framework and have been used to simulate interface crack propagation convincingly. Recent examples include the Virtual Crack Closing Technique (VCCT) [9], the Crack Surface Displacement Extrapolation method (CSDE) [10][11] as well as cohesive zone modelling (CZM) [12]. Moreover, the CSDE method has been applied in conjunction with the cycle jump technique (CJT) [13][14][15] to reduce the calculated loading cycles of fatigue simulations.…”

“…To capture the 3D nature of the problem, the crack propagation in the face-sheet/core and core/PU interfaces was modelled by means of a 3D crack front. By using the mesh at the crack tip, the CSDE mode-mixity method [10][11] was used to extract the energy release rate and mode-mixity along the crack tip front. Each nodal point was able to move independently in a direction perpendicular to the crack front depending on the energy release rate and mode-mixity values, respectively.…”