| Carbon fiber reinforced plastics(CFRP)was widely used in aero-engine cold-end parts(outer casing)as well as the aircraft skin and the wing due to its high specific strength,corrosion resistance,fatigue resistance,material design and excellent impact resistance.The aircraft will be interfered with environmental load during service.The lower bonding strength of the interface between the laminated composite materials is sensitive to the hygrothermal factors for a long time,which may lead to the change of interface properties and the impact resistance of the composite materials.To this end,experimental study was carried out in this paper,including the following three aspects:(1)The hygrothermal aging test of T700/TDE-86 composites was carried out with reference to the hygrothermal aging spectrum of the aircraft materials.The hygroscopic curves of the composites were obtained and analyzed.Composite surface was observed by the scanning electron microscope,and the influence of different hygrothermal aging time on the composite material surface,the fiber/matrix interface and the interface between the layers were discussed.The results show that the hygroscopic process of T700/TDE-86 composites is divided into three stages.In the first stage,the hygroscopic changes accord with fickle’s second diffusion law,reaching the saturated hygroscopicity rate at 140 days,and the saturated hygroscopicity is 1.256%.As the aging time increases,the surface of the resin matrix forms a crack,the fiber/matrix interface debond is generated between the resin matrix and the fiber due to shear stress,and the resin matrix swells to debond the interlayer interface.(2)The interlaminar shear strength specimens,type I and type II interlaminar fracture toughness specimens of different aging ages were tested to obtain interlaminar shear strength,type I and type II interlaminar fracture toughness.With the change of aging time,composite material failure mode changes.The results show that the pre-crack at the tip of type I and type II interlaminar fracture toughness specimens begin to buckle outward under the action of the swelling stress.The interlaminar shear strength of T700 / TDE-86 composite firstly increased and then decreased,the interlaminar shear strength retention rate was 112.36% after aging for 14 days,and the retention rate was 82.16% after aging for 280 days.Because of fiber bridging,type I interlaminar fracture toughness energy release rate were much higher than the non-aging,the retention rate of the first increase and then decline,after 280 days of aging,type I interlaminar fracture toughness energy release rate retention rate of 145.9 %;The type II fracture toughness decline with aging time,retention is 61.34% after 280 days of aging.(3)The ballistic impact experiments with different aging time were carried out,obtaining a rebound condition and breakdown state at three different speeds.The ballistic limit speed of composite was affected by hygrothermal aging.The damage of specimen after impact was observed,and the effect of different states,different impact velocities and different hygrothermal aging time on the failure modes of the composites was analyzed.Ultrasonic C-scan of the impacted composite was performed to analyze the change trend of the damage area.The results show that the ballistic limit of composites increases by 11.5% after 280 days of aging,and the failure mode and the damage area of the composite also change with the aging time and speed of the blade.Therefore,it is of great importance to study the impact resistance of composite structures under hygrothermal aging conditions on the structural integrity of aircraft. |
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