Progressive Damage Analysis of Tapered Composite Laminates

Abstract

Fibre-reinforced composites are increasingly used in aircraft structures as an alternative to traditional metallic components due to their lighter weight and tailorable mechanical properties. However, certifying these materials for critical aircraft components still relies heavily on extensive mechanical testing, which is both resource-intensive and expensive. This reliance highlights the need for virtual testing frameworks that can accurately predict trans-laminar failure behaviour in composite laminates and assess large damage capabilities to create damage-tolerant designs critical for the certification process. Addressing this need, this thesis introduces a novel global-local modelling approach for analyzing trans-laminar damage growth in notched composite laminates. This approach aims to facilitate large-scale structural analysis with reduced computational demands, making it suitable for comprehensive damage assessment in composite aircraft structures.

This research investigates progressive failure analysis in notched composite laminates, with a particular focus on simulating stable damage growth and arrest within the transition region of tapered laminates. A multi-fidelity modelling approach was adopted using flat laminates as a baseline for evaluating damage growth behaviour in the transition regions. Consistent ply stack orientations in both tapered and flat laminates allow for direct comparisons of their distinct failure behaviours. The methodology includes a low-fidelity model that utilizes cohesive elements to simulate self-similar crack growth initiating from notch tips. For more detailed predictions, a high-fidelity model incorporating a discrete ply-by-ply approach with cohesive interactions was used to capture both intra-laminar and inter-laminar damage mechanisms. In this high-fidelity approach, two intralaminar damage models are compared: a user-defined continuum damage model (VUMAT) and a built-in Hashin damage model available in ABAQUS. The VUMAT model applies specific softening laws and element sizes for each failure mode to ensure accurate energy dissipation, while the Hashin model serves as a simpler built-in alternative.

The results show that, despite simplifications, low-fidelity models provide reasonable estimates of failure loads and stiffness in the elastic region, aligning closely with high-fidelity models and existing experimental data. The high-fidelity model effectively captures complex damage modes, with the VUMAT model outperforming the Hashin model in accuracy. The global-local approach proves reliable, offering results comparable to a globally refined meshing approach. It shows potential for use in analyzing larger, computationally demanding structures. Overall, the findings also highlight the importance of fibre-aligned meshing and precise cohesive zone modelling in predicting damage initiation and progression in notched composite laminates, providing insights for designing damage-tolerant composite structures.