Effect of hygrothermal aging on the interlaminar shear strength of a carbon fibre composite

Carbon Fibre Reinforced Plastic (CFRP) composites are used many applications in aerospace structures due to their high specif ic strength and stiffness. Composite aircraft structures are usually exposed to a range of environmental conditions such as hygroth ermal, UVradiation, chemical environments, biological condition etc., in their service life and may degrade. Moisture absorption at different hygrotherma l conditions and its effects on properties of CFRP composites is a useful parameter to designers and application engineers. In this study, UD carbon fiber/epoxy composite laminates were fabricated (HexPly® M21E/34%/UD/194/IMA) from prepreg using standard autoclave process. Inter Laminar Shear Strength (ILSS) test specimens were cut and prepared from theses laminates. Hot-wet specimens were aged at two different conditions; 75 0C/ 85% RH, 55 0C/ 100% RH until attaining moisture absorption saturation. Three-point bend tests were conducted as per ASTM test standard specifications using a 25 KN servo-hydraulic test machine to determine ILSS properties for aged and unaged material. Respective hot -wet conditions were maintained even during the mechanical tests. Tests results show that moisture absorption rate increases gradually and attains saturation at about 1 wt. % under both conditions. Inter laminar shear strength reduced significantly by about 33% due to presence of moisture. Microscopic observation of failed samples also investigated to study the fracture behavior and reported in this paper