Development of a Finite Element Methodology for the Collapse Analysis of Composite Aerospace Structures

Abstract

In this work, an analysis methodology for capturing the critical damage mechanisms leading to collapse in composite stiffened structures is proposed. One aspect of the methodology is a global-local analysis technique that monitors a strength criterion in three-dimensional local models to predict the initiation of interlaminar damage in intact structures. Another aspect of the approach was developed for representing the growth of a pre-existing interlaminar damage region such as a delamination or skin-stiffener debond. This approach is based on applying user-defined multi-point constraints in the skin-stiffener interface that are controlled based on the strain energy release rate as calculated using the Virtual Crack Closure Technique. A separate degradation model was also included to model the in-plane ply damage mechanisms of fibre fracture, matrix cracking and fibre-matrix shear. The complete analysis methodology was compared to experimental results for two fuselage representative composite panels tested to collapse. The two panels had different geometry and material lay-ups, where one panel was tested in an undamaged state and the other had predamage introduced as a result of cyclic loading in the postbuckling region. For both panels, the analysis methodology was shown to be capable of accurately capturing the specimen behaviour and the way in which the various damage mechanisms contributed to the final structural collapse.