Numerical Finite-Element-Analysis of degradation in stiffened CFRP panels

Kurzfassung

The main focus of this degree dissertation was to improve the finite element (FE) tool ABAQUS/Standard (ABAQUS) by writing user subroutines to simulate the degradation of an adhesive between a skin and stringer in a composite panel. In this work simple stress based failure criteria were implemented to predict failure. Preliminary investigations were made on a simple shear plate model, which represented the basic solution for the adhesive modelling of the panel Design 1 (D1) of the COCOMAT project (www.cocomat.com). Based on these experiences, the D1 panel was analysed using the FE software ABAQUS. In the main part of this work three subroutines were developed, the USDFLD, UMAT explicit and UMAT implicit. These user subroutines were used to investigate the shear plate and D1 panel, where the subroutines were used to simulate the degradation of the adhesive layer. From these calculations it was determined that the axial stiffness of both models was reduced significantly and the failure propagation within the adhesive layer was successfully performed through the entire analysis. The USDFLD and UMAT explicit subroutines both gave good results with short analysis times, though both were heavily increment size dependent. The UMAT implicit subroutine gave more accurate results as it used the stresses of the current increment, and was independent of increment size as it applied user-defined criteria to control the increment size, though both of these aspects increased the analysis time considerably. The different user subroutines were then discussed across a range of aspects including accuracy, time consumption, failure stresses and usability, and recommendations were made for the setup, application and improvement of the subroutines.