Comparative study of different modeling approaches for skin stringer delamination growth under postbuckling deformations

Abstract: To improve design methods for damage tolerant composite structures, it is required to successfully develop modeling methods to predict mechanical behavior and failure of complex composite structures such as composite... [ view full abstract ]

Abstract:
To improve design methods for damage tolerant composite structures, it is required to successfully develop modeling methods to predict mechanical behavior and failure of complex composite structures such as composite stiffened panels. The aim of this paper is to assess the energy release rate along the end of the stiffener flange in a stiffened composite panel, and by applying fracture mechanics approach to characterize the growth of the delamination between the skin and the stiffener under compression and shear loading. An analytical approach to evaluate the buckling load of the structure was used as a first evaluation for design, followed by a finite element analysis of two different loading case models in order to compare onset buckling load to experimental results.
Three modeling approaches were provided in order to monitor the energy release rate at the end of the stiffener flange The G-values at the end of the stiffener flange were calculated either by combining the elements forces and the G-values per unit load or by inserting an initial artificial delamination at the end of the stiffener flange. From these results, the Virtual Crack Closure Technique (VCCT) approach was implemented in the critical location of the structure in order to model the delamination growth phenomenon. The modeling approaches were applied to different skin stringer layup in order to assess the effect of stacking sequence on delamination growth. Numerical results are compared with other results from literature and show that are in good agreement in compression case; however, in shear case the correlation with literature approach does not show a good agreement. Comparison between different modeling approaches is explained and selection of method to assess skin stringer debonding is provided. Embedded delamination between skin and stiffener was also investigated; the position and the size of initial disbond were varied to evaluate the effect of postbuckling deformations on inserted delamination growth. Figure 1 and Figure 2 show examples of results related to the behavior of the panel under compression loading and the trends of normalized G values in compression obtained by using different modeling approaches.

Keywords: Stiffened structure, postbuckling deformation, energy release rate, delamination, VCCT.

Corresponding authors: Ahmed.Maslouhi@USherbrooke.ca
Said.Jazouli@aero.bombardier.com