Simulation of Delamination Migration in Laminated Composite Structures - An Approach Combining Extended Finite Elements and a Cohesive Zone Model

Fiber-reinforced polymer matrix composites are being used increasingly in lightweight applications where high strength and stiffness is required. One of the main challenges with designing components from such materials is to predict the ultimate strength and behaviour of the structure. Furthermore, due to anisotropic material response and a complex micro structure, various interacting failure modes exist. In the present work, the interaction between inter- and intralaminar cracks that causes delamination to migrate from one ply interface to another is simulated for cross-ply laminates. A modeling approach that combines the extended finite element method and a surface-based contact formulation with a cohesive zone model is employed. This enables the propagation of arbitrary intralaminar cracks and delamination to be predicted, and non-linear material effects in the process zone ahead of the crack tip can be accounted for. Two experiments from the literature are simulated in order to evaluate the performance and the predictive capabilities of the modeling approach. Differences between experiments and simulations are found regarding the intralaminar crack path and the force-displacement response of the structure. However, the series of unstable fracture events, including delamination migration is successfully simulated. The predicted delamination length, crack direction and migration location is in good agreement with the experimental results. The presented approach is computationally demanding and lacks flexibility but shows that with further improvements, more efficient and accurate modeling techniques can be developed based on the same concepts.How can the failure of a fiber reinforced composite structure be predicted? This is one of the key issues that any engineer must deal with when designing lightweight components in such materials. Yet, it is not fully understood how the different failure mechanisms interact with each other, and the complex material modeling offers several challenges. In this master thesis, a modeling approach is developed that is able to predict the interaction between interface cracks and ply cracks, which causes delamination to migrate