Abstract

Composite materials, especially carbon fiber reinforced polymers (CFRPs), have been broadly used due to their high specific strength and stiffness ratio compared to metallic materials in the past few decades. CFRPs are widely utilized in aerospace, civil infrastructure and marine sectors under harsh environments. As a result, there exists a strong demand to observe the mechanical behavior of composite materials in the presence of moisture in order to avoid unpredictable effects. Composite structures are often cured in an autoclave to achieve the required aerospace grade quality. However, curing large structures requires access to large autoclaves which is limited and expensive. As a result, fabrication of large structures using out-of-autoclave prepreg materials will lead to a great amount of savings in manufacturing costs. In the out-of-autoclave processing method, the presence of voids inside the laminate has been an issue due to the lack of high pressure during manufacturing. This study aims primarily to observe the moisture absorption response of composite samples containing different levels of void. By changing the vacuum level inside the bag during the manufacturing process, three different unidirectional laminates at three levels of void have been manufactured. After immersing the samples in warm water at 60˚C for about one year, the maximum moisture absorption level and rate of absorption were monitored through experiments and diffusion coefficients were calculated for all the samples using Fick’s law. Results show that the moisture absorption coefficient, its rate and the maximum level of moisture can be correlated to the void volume fraction. Moreover, the sensibility of the CFRPs under moisturized environment has been investigated. The mechanical behavior of these laminates has been studied at four different moisture levels by performing dynamic mechanical analysis (DMA) and interlaminar shear strength (ILSS) tests. Empirical results indicate that in most of the cases, interlaminar shear strength, glass transition temperature, and storage modulus decrease during the exposure of the samples with different void contents to the moisture environment. Finally, a finite element analysis has been done to study the change of moisture concentration through the thickness of the material.