Experimental Investigation On The Hygrothermal Ageing Of Carbon Fiber Reinforced Vinylester Resin Composites

Carbon fiber reinforced polymers(CFRP)are widely used in the manufacture of marine equipment because of their excellent corrosion resistance and outstanding mechanical properties.In the complex marine environment,CFRP are exposed to humid and thermal environment for a long time.The diffusion of moisture seriously affects the mechanical properties of CFRP,which brings great hidden danger to the safety of the structure.In order to guarantee the structural safety while taking into account environmental protection and economic benefits,the durability and aging mechanism of CFRP under hygrothermal environment need to be studied.In this paper,the hygroscopic behavior and mechanical properties of carbon fiber reinforced vinyl resins in two hygrothermal environments,deionized water at 70°C and artificial seawater at 70°C,were investigated by artificial accelerated aging experiments,while pure vinyl resins were prepared as a control group for simultaneous study to explore the different roles of carbon fiber and resin matrix in the hygrothermal aging process.The diffusion behavior of water molecules in the composites directly affects the durability of the materials in the environments.The surface morphological changes caused by the erosive effects of water on the specimens were observed by scanning electron microscopy(SEM),while Fourier infrared spectroscopy(FTIR)was used to analyze the chemical changes occurring in the polymer molecular chains on the surface of the specimens in the hygrothermal environment.The results showed that the hydrolysis of the resin molecular chains and the loss of hydrolysates in the medium led to the formation of a large number of pores on the surface and the appearance of the channels inside the specimens after the pure resin specimens immersed in deionized water for 90 days.The results of high performance liquid chromatography-mass spectrometry(HPLC-MS)confirmed the presence of a significant amount of hydrolysates in the medium.The pores on the surface of the pure resin specimens immersed in artificial seawater were much less than those in deionized water.Because the carbon fibers which are hydrophobic inhibited the diffusion of water molecules,no cracks and pores were found in CFRP specimens soaked in both environments.The water uptake of the specimens for different exposure time intervals was obtained by weighing the specimens exposed to hygrothermal environments,and the water uptake was established as a function of exposure time.The results showed that the pure resin conformed to Fickian diffusion in artificial seawater,while it exhibited significant nonFickian diffusion behavior in deionized water,which was the result of the coupling effect of diffusion-controlled moisture absorption and hydrolysis-controlled moisture absorption.CFRP conformed to Fickian diffusion in both hygrothermal environments.Carbon fibers inhibited the absorption and diffusion of water in CFRP,resulting in a lower saturated water uptake in CFRP specimens than in pure resin specimens.To evaluate the effects of the two hygrothermal environments on the mechanical properties of CFRP and pure resin,the tensile strength/modulus and compressive strength/modulus of CFRP and pure resin,the in-plane shear strength/modulus and interlaminar shear strength of CFRP were tested,and the mechanical properties of CFRP at two extreme temperatures,elevated temperature(70°C)and cryogenic temperature(-30°C),were also characterized.The test results indicated that the mechanical properties of CFRP and pure resin showed different degrees of degradation after aging,and there was no significant difference in the degradation effect on the mechanical properties of the specimens caused by the two hygrothermal environments.The effects of high temperature on the mechanical properties of CFRP was greater than that of the hygrothermal environment.