Study On Polymer Degradation Behaviors Of T700/6421Composite In Various Environment Conditions

According to the service environment of composite materials in the aerospace field，T700/6421composites was processed under vacuum thermal cycling at the continuouslychanging interval of-120~100℃and hydrothermal aging under100℃/RH100%and80℃/RH90%. Evolution rules of mass loss rate, moisture absorption rate and mechanicalproperties of the materials under different environments were investigated. SEM，FTIR-ATR， DMA and Hopkinson impact bar were used to characterize the fracture surfacemorphology, the microscopic structure and dynamic mechanical properties of composites.The experimental results show that the mass loss rate of the composites firstly increases withincreasing vacuum thermal cycles and begins to increase gradually after48cycles. Under thecombined influence of physical aging， post curing and thermal stress， the transverse tensilestrength and interlaminar shear strength (ILSS) of the composites was observed to reduce,which undulated at the beginning of the vacuum thermal cycles and tended to level off afterabout100cycles. Transverse tensile strength decreased by21.14%and ILSS decreased by6.57%in the final. The bend strength was seen to increase at the initial stage of thermalcycling and decrease after50cycles，which tends to be smooth after approximate100cycles.The bend strength increased by16.3%in the final. Obvious physical aging and some degreeof post curing occurs due to vacuum thermal cycles, as evidenced by the interfacial debonding,microcrack expansion and increases in the high temperature storage modulus and Tgof thecomposites.Under different conditions of hydrothermal aging， the moisture absorption behaviors ofT700/6421composites basically conform to Fick’s second law. Moisture absorption causeddamage to interlaminar interface， which lead to a large number of voids and cracks. Thesaturated moisture content increased slightly and weight gain of the T700/6421composite is1percent after desorption. The transverse tensile strength and ILSS continuously decreasedwith the growing absorption rate， which still reduced after desorption in the case of100℃/RH100%and slightly recovered for a80℃/RH90%specimen. The bend strength increased with the growing absorption rate and still increased after desorption. The results of thehopkinson bar test indicated that the T700/6421composite was strain rate-dependent material.The Young’s modulus increased with increasing the strain rate. It is found after hydrothermalaging that the Young’s modulus and plastic deformation of the composite increase and thestrength is almost invariant.