The Effects Of Hygrothermal Aging On Mechanical Properties Of C/HT280 Composites

With the rapid development of aerospace,the application of resin-based composites in aircraft is becoming more and more widely used.Long-term in a hygrothermal environment,the composite will undergo different degrees of aging,damage or even damage,which in turn affects the safety and stability of the aircraft.In this paper,T700/HT280 composites and HT280 resin were used as research objects to simulate the hygrothermal environment.The aging mechanism of materials before and after hygrothermal treatment was analyzed by means of infrared spectroscopy,dynamic mechanical thermal analysis,scanning electron microscopy and ultrasonic C-scan.The effects of hygrothermal aging on tensile properties,creep properties and tensile-tensile fatigue properties of T700/HT280 composites and their matrix resins were investigated.The research results are as follows:As the hygrothermal aging time increases,the moisture absorption rates of the resin and composite increase rapidly and then level off,which are in accordance with the Fick's second law.The maximum moisture absorption rate of resin is stable at about 3%.the maximum moisture absorption rate of composite is stable at about 1%.The long-term hygrothermal environment treatment causes the hygrothermal physical aging of the resin.Under the action of moisture absorption and hygrothermal stress,the composites show different degrees of interface debonding.With the increase of hygrothermal time,the tensile strength of the resin and the tensile strength curve of resin after creep change consistently,and both increased first and then decreased.The creep curves of the resin before and after the hygrothermal aging show a trend of rate decay.Through model fitting and experiment comparison found that the three-parameter time hardening model has the best creep fitting effect and the Poynting-Thomson model is the second.The Kevin model has poor fitting accuracy.The three-parameter time hardening model can predict the creep curve better,which is helpful for the investigation of long-term resin creep.With the increase of hygrothermal aging time,the tensile strength of T700/HT280 composites increases and then decreases,and the interlaminar shear strength showed a monotonous downward trend.The tensile strength of the materials before and after hygrothermal aging is higher than 800 MPa,indicating that the material has good hygrothermal resistance.The variation of interlaminar shear strength indicates that the interface debonding degree increase gradually under the action of moisture absorption and hygrothermal stress.The stiffness degradation curves of the original specimens at 60% and 65% stress levels follow the "fast-slow-fast" trend which presents a complete three stages of stiffness degradation.The stage III of the stiffness degradation curve and the area of the hysteresis energy curve can effectively characterize the environmental damage effects induced by the hygrothermal environment factors.