Influence of humid environment on the performance of high strength structural carbon fiber composites

This paper reports moisture absorption behavior and its effect on mechanical performance of carbon fiber reinforced epoxy composite laminates made from 913C-HTA 12K 5–34%. Longitudinal tensile, transverse tensile and in-plane shear properties were measured using [0]8, [90]10 and [±45]10 laminates as a function of moisture absorption. The results revealed that the rate and amount of swelling in through thickness was more as compared to longitudinal and transverse directions. The longitudinal tensile strength dropped by 25–30% during first month of the exposure period and remained constant within the experimental scatter during rest of the exposure time. The transverse tensile strength showed decreasing trend during exposure period. Longitudinal tensile modulus decreased during first 2 months of exposure time and remained constant during rest of the exposure time. In-plane shear strength showed increasing–decreasing trend during the exposure period. Transverse tensile modulus, in-plane shear modulus and Poisson's ratio remained constant during the exposure period. Finally, the possible mechanisms for the failure are discussed.