Degradation investigation in a postbuckling composite stiffened fuselage panel

Abstract

The European Commission Project COCOMAT (Improved MATerial Exploitation at Safe Design of COmposite Airframe Structures by Accurate Simulation of COllapse) is a currently running four-year project that aims to exploit the large strength reserves of composite structures through a more accurate prediction of collapse. Accordingly, one of the COCOMAT work packages involves the design of test panels with a focus on investigating the progression of composite damage mechanisms. This paper presents the collaborative results of some of the partners for this task. Different design alternatives were investigated for fuselage-representative test panels. Non-linear structural analyses were performed using MSC.Nastran (Nastran) and ABAQUS/Standard (Abaqus). Numerical predictions were also made applying a stress-based adhesive degradation model, previously implemented into a material user subroutine for Abaqus. Following this, a fracture mechanics analysis using Nastran was performed along all interfaces between the skin and stiffeners, to examine the stiffener disbonding behaviour of each design. On the basis of the structural and fracture mechanics analyses, a design was selected as being the most suitable for the experimental investigation within COCOMAT. Though the COCOMAT panels have yet to be manufactured and tested, experimental data on the structural performance and damage mechanisms were available from a separate project for a panel identical to the selected design. This data was compared to the structural, degradation and fracture mechanics predictions made using non-linear finite element solutions, and the application of the design within the COCOMAT project was discussed.

Global behaviour of a composite stiffened panel in buckling. Part 1: Numerical modelling

“…However for a panel in compression it has been noticed that debonding of the stringer is not the source of the post-buckling failure for a prepreg co-cured stiffened panel [12], whereas it has been observed on a co-bonded stiffened panel at the element level [5] and it is combined with delaminations and fractures in the skin and the stringer flanges at the panel level [4,17]. As a distinct bonded interface is missing, panels manufactured by LRI from dry fabrics are intended to be a little different from those manufactured from co-bonded and co-cured structures made of prepregs.…”

“…Comparison between several composite panel finite element models made of prepregs exist [4] using Nastran and Abaqus solvers and take into account geometrical imperfections and a stressbased degradation methodology applied to the adhesive layer at the skin-stiffener interface. These authors also explain how delamination occurs [5] and implement a global-local approach where the deformation field of a global shell model is incorporated at the boundary conditions of a three-dimensional model of a skinstiffener interface.…”

Experimental and Numerical Analysis of the Compression of a Thin-Walled Composite Plate

“…These are the decisive features for the use of thin-walled composite elements as support elements in the automotive [2], the aerospace [16,18,22] or the space industry where there are quite rigorous performance requirements regarding the structure work in the complex load conditions. The specificity of thinwalled supporting structures causes that in case of a specific state of the load its elements can be exposed to the possibility of loss of stability within the exploitation load conditions.…”

Global behaviour of a composite stiffened panel in buckling. Part 2: Experimental investigation

“…The load at collapse will be used to set-up the test. Geometric imperfections of the skins are not considered since they have an almost negligible effect on the load at collapse [9]. The side stiffeners provide enough rigidity so that the panel borders do not buckle [7].…”