The Effects Of Air Thermal Cycling On Mechanical Properties Of T700/HT280 Composites

T700/HT280 composites and HT280 bismaleimide resins used in this research were subjected to the air thermal cycling treatment.The aging mechanism of the mentioned above materials before and after air thermal cycling was analyzed by using infrared spectroscopy?IR?,dynamic mechanical analysis?DMA?,ultrasonic C scan testing methods.The tensile and tensile-tensile fatigue properties of T700/HT280 composites as well as the creep behaviors of HT280 resins were tested,respectively.It was shown in the experimental results that the laminate configuration had little effect on the mass loss rate of composites,and the mass loss rate of HT280 resins was greater than that of T700/HT280 composites.The mass loss was mainly attributed to the volatilization of low molecular weight substances in HT280 resin.Air thermal cycling treatment gave rise to the obvious oxidation and thermal aging of HT280 bismaleimide resins.The glass transition temperature?T_g?of T700/HT280unidirectional composites was greatly affected by the interfacial damage.The T_g of multi-ply composites were significantly influenced by the post curing and thermal aging of the resin matrix.The effect of thermal aging on T_g of resin matrix was more remarkable than that of post curing.The tensile strength curves of T700/HT280 unidirectional composites and T700/HT280multi-ply composites showed a tendency to increase first and then decrease,which was attributed to the comprehensive effects of post curing,interfacial debonding and thermal aging in the process of air thermal cycling.As the number of air thermal cycling increases,the tensile strength of HT280 resin presents a decrease-increase-decrease trend.After the air thermal cycling treatment,the tensile-tensile fatigue curves of T700/HT280multi-ply composites basically conformed to the"fast-slow-fast"rule manifested in the shorter fatigue life and the decreased fatigue resistance.The air thermal cycling treatment was responsible for the slowly decreased stiffness and the decreased fatigue resistance of the T700/HT280 unidirectional composites.The creep speed of HT280 resins showed a decay trend after air thermal cycling treatment,which was ascribed to the combined interactions of evaporation of low molecular weight substances,post curing and thermal aging of resin matrix.The time hardening model was more suitable than the Kelvin model to accurately describe the creep behavior of the samples before and after the air thermal cycling treatment.