Abstract: The T300/E51 composites are treated by electrothermal treatment, hygrothermal ageing and electrothermal moisture treatment. The effect of electrothermal treatment on the hygrothermal ageing is revealed from bending properties, moisture absorption rate, chemical structure of the matrix, glass transition temperature, bending fracture and etc. The results show that the original sample is hydrolyzed partially after the hydrothermal treatment, and the samples processed with 4 A electro-thermal and hydrothermal treatment have an obvious postcure effect, while there is no significant change in the samples after 6 A electro-thermal and hydrothermal treatment. The moisture absorption rate of 4 A heated sample is decreased due to the decrease of the size of interface cracks caused by postcure effect. The variation of glass transition temperature is similar to that of bending behavior. The detailed analysis reveals that, the damage mechanism of T300/E51 composites after electrothermal treatment is different from that of traditional moisture. The glass transition temperature becomes a primary factor to measure the performance of composite materials, instead of moisture absorption. Microstructure observations show that the micro-cracks are increased owing to the temperature gradient and compressive stress generated by the effect of electrothermal treatment. Additionally, the swelling occurs throughout the matrix after the subsequent hydrothermal treatment, which eventually leads to the decrease of the bending property.

Key words: carbon fiber/epoxy composite, electro-thermal treatment, hydrothermal aging, microstructure