Novel methodology for predicting delamination in 3D composite structures under multiple loading conditions and large process zones

ENG- The overall objective of this thesis is to provide a tool for predicting delamination in composite materials under different static and fatigue loading conditions in 3D structures. The methodology is intended to be a practical guide for industry, providing a flexible tool capable of predicting the delamination behaviour of new polymeric materials in an agile manner. A review of the state of the art has shown that there is still some missing link between the physics responsible for delamination and the state of the art models, especially for materials with large delamination process zones. There is also a lack of validation tests that challenge the delamination predictions under different loading conditions in 3D structures. This work contributes to the field of delamination characterisation in composites with large process zones and builds a modelling and simulation strategy capable of predicting delamination in composites with large process zones. A comprehensive validation of the delamination prediction is also presented. For delamination characterization, test procedures and data reduction methods that are suitable for characterizing the delamination properties are summarized and the most suitable techniques for characterizing large process zones are discussed and selected. For the modelling and simulation strategy, the Cohesive Zone Modeling (CZM) approach is selected to predict the delamination behavior. State-of-the-art static and fatigue CZM models are used as the core of the simulation strategy, while novel developments are integrated, aimed at linking the simulation approach with the physics of the delamination observed experimentally. To validate the modelling and simulation strategy, a novel delamination benchmark test concept for composite materials that allows non-straight crack fronts and non-self-similar delamination in characterization specimens under complex loading conditions is presented. As validation of the modelling and simulation strategy, a blind simulation of the benchmark test is proposed to evaluate the predictive capabilities of the methodology. Finally, the proposed methodology is exemplified by a case study illustrating the application of the methodology to a real composite material with a large process zone. The material used in the case study is the AS4D/PEKK-FC thermoplastic composite, exhibiting large delamination process zones