On the durability of FRP composites for aircraft structures in hygrothermal conditioning

The main focus of this work is to built an experimental database which may be helpful to the research and development on the design and qualification of composite repairs for aircraft structures. Glass-epoxy (G-E), carbon-epoxy (C-E) and hybrid laminated bidirectional composites were manufactured, characterized and then compared. The influence of hygrothermal conditions on p erformance of such fiber-reinforced polymer (FRP) composites was also investigated. Several durations of conditioning at 24 ± 3, 70 and 90 °C in distilled water were retained. Both time and aging temperature were combined in order to better highlight the impact of aging on the performance of the studied composites. When exposed to water, all composites displayed a Fickian sorption behavior. Due to its hydrophilicity and its polarity, G-E composites showed the greater diffusion coefficient and the maximum moisture content. Whereas, the C-E composites exhibited the best mechanical behavior when they are subjected to tensile, flexure and wear.On the other hand, over prolonged periods of immersion, water induced a noticeable degradation and resulting structural changes were recorded indicating that the durability of these composites was affected. In particular, G-E composites showed higher sensitivity to aging in comparison with C-E and hybrid composites. In all cases, the reduction in mechanical properties is caused by matrix plasticization due to moisture and temperature. Finally, the study of time temperature superposition (TTS) allows establishing a correlation between exposure to moisture and temperature and the mechanical behavior for the studied laminated.