Effects Of Hydrothermal Aging On The Mechanical Properties Of T-700 Carbon Fiber / Epoxy Resin Composites

Paper number

IAC-07-C2.I.11

Author

Mr. Chen XiaoPeng, The 41st Institute of the Sixth Academy of Aerospace Science & Industry Corp, China

Year

2007

Abstract

Carbon fiber/epoxy resin composites used for solid rocket motor case were aged at different temperatures and humidity for various amounts of high-low temperatures circles times. Water sorption follows a Fickian law (activation energy of 11.5kcal/mol) and seemed to be controlled by the epoxy matrix. This paper was focused on investigating the effects of hydrothermal aging on the mechanical properties of T-700 carbon fiber reinforced epoxy resin composites molding by different process.

    In this study, the reinforcing materials are unidirectional cloth and tabby cloth, and both of them are weaved by T-700 carbon fiber. The epoxy matrix is TDE-85/MTHPA acid anhydride system. The samples were prepared by filament winding, lay-up/RTM, compression molding respectively. Tensile strength, compressive strength, bending strength and interlaminar shear strength were employed to characterize the mechanical properties of the composites. Aging was carried out by placing the samples into thermal and wetting aging box, in where the relative humidity was 95 percent, and the temperature was 30 degree Celsius, up to 60 degree Celsius,then back to 30 degree Celsius, calefactive ratio was 0.5 degree Celsius/min during each calefactive phase, each constant temperature phase lasts for eight hours. So each whole circle was 24 hours and the test circulated for 10 times. At last, the SEM pictures of the samples with aging and without aging were taken to observe the variation of the interfacial bond quality even after hydrothermal ageing, the employed strength were compared and analyzed to shown the influence of the aging.

    After ten hydrothermal aging circulating, the variation of strength resistivity with moisture and temperature aging shows two different regimes. Composite tensile strength changes little, yet the interlaminar shear strength, bend strength, compressive strength decrease obviously. The SEM images of the samples’ profiles indicate there have the great difference between the samples that through hydrothermal aging cycles and the others without aging. After aging, the matrix was loosened, and bonding interface between fiber and resin became clear, matrix desquamated from fiber evidently. 

    The effect of moist heat on interfacial bond performance is further analyzed based on the basic theoretical. The SEM pictures show the interfacial bond state of humidity aged samples. It can be seen that the moisture absorption ability of the resin is high, that is because of lots of hydrophilic hydroxyl groups existing in the molecular structures of the cured epoxy resin matrix. These hydrophilic groups led to swelling and plastication inside the matrix, as well as softening the matrix, by which the matrix degenerated and weakened the interfacial bond adhesion capability of the matrix. So after hydrothermal aging cycles, the part of employed mechanical property of composites decreased obviously. Yet the moisture absorption ability of carbon fiber is low, little degeneration happened after aging cycles. Thus different hygroscopic ratios lead to desquamating between fiber and matrix. Longitudinal tensile strength and modulus that conducted by fiber degenerated little, on the contrary, the longitudinal compressive strength, interlaminar shear strength and flexural strength that was influenced mainly by matrix degenerated obviously.

Abstract document

IAC-07-C2.I.11.pdf

Manuscript document

IAC-07-C2.I.11.pdf (🔒 authorized access only).

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