| Περίληψη: | In aeronautical applications, structures are exposed to severe cycles of environmental conditions that involve changes in temperature, humidity, oxidation, etc., as well as a combination of environmental conditions in the presence of mechanical stress over long periods of time, causing degradation, and damage to materials. The combination of extreme environmental conditions and mechanical loading during the operation of the structure, affects the strength and hence the lifetime of the construction and is directly related to its operational safety and maintenance costs. The main purpose of the present thesis was to study the effect of hydrothermal ageing on the mechanical properties of different types of composite materials. In the framework of this study, the behavior of epoxy resins (nano-reinforced and non-reinforced), epoxy and cyanate ester resin fiber reinforced composite materials (nano-reinforced and non-reinforced), as well as the behavior of flax fiber reinforced composites using different types of bio-based resins was examined. A basic concept on which this PhD thesis was based was the study and investigation of the behavior of composite materials of different types under hydrothermal ageing conditions. The kinetics of water sorption in different types of composite materials, is widely studied using Fickian, Langmuir and Dual Stage diffusion models. In all types of composite materials examined, the degradation of the mechanical properties due to hydrothermal ageing is investigated, and the process of potential recovery of the properties is considered when the absorbed water is lost for some reason. In all chapters of the present thesis, there is an analytical effort to explain the findings and documentation of ageing mechanisms.
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