Mode-I fracture toughness of hygrothermally aged curved filament-wound carbon and glass fibre composites

This work aims to assess the effect of hygrothermal ageing on the Mode-I fracture toughness behaviour of glass/epoxy and carbon/epoxy composite structures manufactured by filament winding. Cylinders (136 mm in diameter) are manufactured using various winding angles (±0°, ±15°, ±30° and ± 45°), and the specimens are aged in water at room temperature and 70 °C. Water uptake was monitored until equilibrium, which varies with the material, temperature, and winding angle, being the highest for the ± 45° sample, reaching 1.10 % for glass/epoxy and 1.74 % for carbon/epoxy at room temperature, and 1.30 % and 2.95 % at 70 °C. These results are related to the void content, which is 3.20 % and 3.41 %, respectively. Glass/epoxy composites show superior performance in terms of peak load and strain energy release rate, but carbon/epoxy shows higher fracture toughness for the same winding angle and ageing. Specimens aged at room temperature are less prone to delamination than those at 70 °C. In addition, aged samples at room temperature show higher peak force and strain energy release rates compared to non-aged composites, which is attributed to matrix plasticisation. Samples aged in hot water have poorer behaviour compared to those non-aged or aged at room temperature. The curved double cantilever beam (CDCB) samples have more complex fracture mechanisms compared to flat samples, attributed to their curvature and difficulty in keeping symmetry throughout the test.