Towards fundamental understanding of interlaminar ply delamination growth under mode II and mixed-mode loading

Abstract

In a context of many studies addressing delamination growth in laminated composites, this thesis provides understanding of the underlying physics of this phenomenon. The models currently used to assess delamination growth are phenomenological in nature and rely almost solely on curve fittings and experimental data. These empirical models are used to predict delamination growth rather than aid in understanding it. This lack of knowledge on the physics of delaminations causes problems for both academia and industry. From the perspective of academia, science needs to be built upon fundamental understanding. However, this is currently not the case for delamination growth. Phenomenological trends, for which the reasons are not yet clear, are assumed as fact, and science tries to advance building on these trends. Meanwhile, from the perspective of industry, engineers compensate for the lack of fundamental understanding with conservativeness, overdesign and a great amount of tests, yielding extra costs. Therefore, the present thesis seeks to understand the fundamentals of delamination growth by physically characterising it. This characterisation is performed relating the strain energy dissipated in delamination growth with the delamination growth rate and the damage mechanisms encountered on the fracture surfaces. To this aim, carbon-epoxy unidirectional laminated specimens were manufactured and tested under mode II and mixed-mode static and fatigue loading. Fracture surfaces were analysed on a Scanning Electron Microscope, and the damage mechanisms were identified and correlated to the strain energy dissipated...