Hygrothermal effect on the fracture/fatigue behaviour of adhesively bonded repairs

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Structural applications of composite materials have been increasing in the transportation industry because they present good mechanical properties (high stiffness and strength) associated with low weight. They enable fuel saving and performance improvement. However, composite components are prone to delamination damage, mainly under bending loads. Because of this issue, locally damaged regions can compromise the complete structure, which leads to premature replacement of large structural components with obvious economic and ecological costs due to waste of material. Therefore, a viable alternative is to repair damaged components. Adhesive bonding is becoming one of the most suitable and attractive techniques for joining and repairing composite parts and it has proven to be very effective (uniform stress distribution over the bonded area, less weight penalty and higher fatigue and corrosion resistance). Nevertheless, before its complete implementation, it is necessary to fully understand its behavior under fatigue, which is a predominant type of loading in the transportation industry. In these applications, structures are also frequently under severe environments, making it essential to evaluate the influence of hygrothermal conditions (moisture and temperature) on their mechanical behavior. Thus, it is important to develop numerical predictive tools that take into account the combined effect of the environment and fatigue. However, such numerical works are rather scarce and the majority of tools are semi-empirical; which means that they require extensive experimental testing to fine-tune the models. The current proposal aims to develop a progressive damage model incorporating the effects of fracture, fatigue and environmental degradation. Such model will be based on suitable “ageing factors” derived from appropriate relations as Fickian diffusion models and the experimental Paris curves.