Effects of moisture absorption on mechanical and viscoelastic properties in liquid thermoplastic resin/carbon fiber composites

Abstract

This article investigated the effect of moisture on the tensile strength and in‐plane shear of laminated composites. For this, the results of a composite system based on a new thermoplastic Elium® 150 resin were compared to a traditional epoxy resin result. Both composites were fabricated via VARTM using a 0/90° plain weave carbon fiber fabric. For the non‐conditioned specimens, the thermoplastic composites presented 30% more tensile resistance in comparison to epoxy composites. For conditioned specimens, this difference was 14%. These results were related to plasticization, which tends to favor the polymer softening providing a greater matrix plastic deformation, promoting a ductile fracture of the composite. On the other hand, the in‐plane shear properties were 30% higher for the thermosetting laminates for both conditions. In this case, moisture may have favored the formation of surface cracks and weakened the fiber/matrix interfacial adhesion. Additional analysis based on design of experiments has shown that the Elium® 150 resin significantly affects all responses and presented in fact a better behavior in comparison to Epoxy resin. While the conditioning effects have featured a statistically noticeable contribution to the tensile strength, the presence of the moisture did not provide a significant enhancement to the in‐plane shear strength. Besides that, the unknown fractographic aspects of the fracture surfaces of both composites were used as a complementary tool for the mechanical characterization. POLYM. ENG. SCI., 59:2185–2194, 2019. © 2019 Society of Plastics Engineers