Hygrothermal aging on pultruded carbon fiber/vinyl ester resin composite for sucker rod application

The effects of hygrothermal aging on thermal and mechanical properties, and on the microstructure of pultruded unidirectional carbon fiber/vinyl ester resin (CF/VE) composites were investigated. The composite specimens were immersed in distilled water and salt solution at 95 and 65 degrees C for more than 1000 h and the moisture absorption was recorded. The diffusion rate of moisture into the composite was found to fit Fickian's diffusion model. SEM observation revealed that the fiber-matrix interface was weakened due to the invasion of moisture leading to debonding. Three-point flexural and interlaminar shear tests showed that both flexural strength and interlaminar shear strength (ILSS) of the composite specimens deteriorated to some extent after hygrothermal aging, while stiffness was less affected. Dynamic mechanical thermal analysis (DMTA) results indicated that the glass transition temperature of the matrix underwent complicated changes, which was attributed to the combinational effects of plasticization and the formation of hydrogen bonds in the systems.