Observing the evolution of fatigue damage and associated strain fields in a correlative, multiscale 3D time-lapse study of quasi-unidirectional glass fibre composites

This research is focused on studying the tension-tension fatigue behaviour of a unidirectional (UD) glass-fibre wind turbine composite. The damage features, their progression and the associated strain fields are tracked in a representative volume by employing a novel correlative approach bringing together x-ray computed tomography (XCT) and digital image correlation (DIC). The focus is on studying ex situ the evolution of damage features (fibre breaks and micro cracks) in an interrupted time-lapse manner. The major drops in stiffness are correlated to the number and location of the damage features in the bulk (XCT) and at the surface (DIC). Results from XCT highlight a localized cluster of fibre breaks and matrix cracks near backing bundles along with axial macro-cracks, while DIC shows that the backing bundles cause regions of higher strain. This highlights the relation between the damage features and strain localisation and their effect on the progressive degradation in stiffness during high cycle fatigue (HCF) cycling.