Design and Analysis of Composite Panels

Abstract

European aircraft industry demands for reduced development and operating costs, by 20% and 50% in the short and long term, respectively. The European Commission project POSICOSS, which lasted from January 2000 to September 2004 and the 4-year follow-up project COCOMAT, which started in January 2004, contribute to this aim [1]. Both projects are under the co-ordination of DLR, Institute of Composite Structures and Adaptive Systems. They reduce structural weight by exploiting considerable reserves in primary fibre composite fuselage structures through an accurate and reliable simulation of postbuckling and collapse. The POSICOSS team developed fast and reliable procedures for postbuckling analysis of fibre composite stiffened panels, created experimental data bases and derived design guidelines. The COCOMAT project builds up on the POSICOSS results and goes beyond by simulation of collapse. The project improves existing tools as well as design guidelines for stiffened panels taking skin stringer separation and material degradation into account and it creates a comprehensive experimental data base.The improved tools, developed within the POSICOSS and COCOMAT project, have to be validated by test results. Since appropriate test data bases were not available, both projects were constrained to create new experimental data bases for curved stringer stiffend CFRP panels. To that end suitable panels are designed, manufactured, inspected and tested under own project objectives. Each project differentiates between verification panels and industrial panels. The verification panels are designed as to specific limiting aspects of application of the software to be verified, e.g. small or large stiffness reduction in the postbuckling regime. These panels should have a significant postbuckling range up to collapse and have an early onset of degradation. The industrial panels were designed in regard to industrial applications, mainly by existing procedures used in day-to-day industrial design practice.For the analysis of the panels the partners utilized different finite element software tools. This paper focuses on the experience of DLR on the design and analysis of stringer stiffened CFRP panels gained in the frame of the POSICOSS and COCOMAT projects. Geometrical nonlinear computations up to collapse were performed applying the software ABAQUS/Standard. The material was assumed linear elastic. The onset of degradation of the structure and the skin-stringer connection was determined using different failure criteria. Results achieved so far will be presented and an outlook towards future activities will be given.