Simulation of stringer stiffened CFRP panels in consideration of skin-stringer separation

Abstract

The first main focus of this work was to improve and investigate the sensitivity to various parameters of previously developed user subroutines for the finite element (FE) tool ABAQUS/Standard (ABAQUS). These subroutines are aimed at the realistic simulation of degradation of an adhesive layer between a skin and stringer in a composite panel. In this work, simple stress based failure criteria were implemented to predict failure. The influence of numerous parameters on the numerical stability, the accuracy and the time consumption of the nonlinear FE analysis was tested for several versions of different subroutines. These parameters included changes in geometry of the model and the number and location of elements and changes in the subroutine code itself. Different stress based failure criteria were applied and investigated. Also the code for the subroutine USDFLD was improved and extended in order to give a more realistic prediction of element failure in the adhesive layer. Analyses were performed for the Design 1 panel (D1) of the COCOMAT project [5]. The results were compared across a range of aspects including accuracy, time consumption, failure stress and usability. The other main focus of this work was the investigation of numerous possible influences on the buckling behavior of the D1 panel. Numerical simulation were performed including different geometric imperfections to evaluate the influence of these imperfections on the axial stiffness, the load-carrying capacity, the buckling mode shapes and the collapse point of the panel. These results were compared to the data previously collected during the experimental testing of a panel similar to the COCOMAT panels. The different influences were described and discussed and recommendations were made for the setup, performance and validation of the COCOMAT panels, which will be tested at the DLR in the spring of 2006.