The Study Of Measurement Of Deformation And Damage Of Fiber-Reinforced Composites After Seawater Aging

Composites are widely used in aviation,automobile,maritime affairs and other fields because of their excellent properties such as high specific strength,high specific stiffness and light texture.Some properties of composites will deteriorate in seawater,damp heat,high temperature or other environmental conditions for a long time,thus affecting their service life.In this paper,carbon fiber plain woven composites,glass fiber plain woven composites and carbon/glass hybrid composites specimens with different laying methods were soaked and aged in artificial seawater.Acoustic Emission(AE)technology and Digital Image Correlation(DIC)method are used to monitor the bending loading failure process of composites aged in seawater in real time.The AE response behaviors and deformation field information of different types of composites specimens after aging in seawater under bending load are obtained,and the bending deformation damage behaviors of fiber reinforced composites after aging are analyzed.The main conclusions are as follows:(1)The flexural strength of carbon fiber woven composites aged for 1344 hours is the lowest.According to the characteristic parameter information of AE signals such as amplitude,cumulative number,duration time and the information of deformation field,it can be found that the longer the aging time is,the higer the amplitude will be.And the AE signals with high duration time will be generated earlier.In addition,the moment when the cumulative hits of AE signals rising sharply is earlier under bending loading.The AE signals with the amplitude of 40-60 dB are almost the densest,and the number of AE signals above 60 dB is the largest.With the increase of aging time,the value of maximum strain of the specimens in the horizontal direction is increasing in the low load.The value of surface strain of the specimens aged for 1344 h along the loading direction is up to 26.698%,and the range of the high strain area of the specimens increases.(2)The flexural strength of glass fiber plain woven composites decrease gradually with the increase of aging time,and the retention rate of flexural strength of specimens aged for1344 hours is 80.53%.According to the number and amplitude of AE signals,the damage process of specimens with different aging time can be divided into damage accumulation stage and damage failure stage.Compared with the specimens aged for 0,168 and 336 hours,the specimens aged for 672,1008 and 1344 hours generate AE signals with fewer number,lower energy and shorter duration time in the damage accumulation stage,and the AE signals of 80-100 dB collected in the damage failure stage gradually decrease.Based on the strain field information,the differential value between tensile and compressive strain is the largest,the range and degree of delamination are more obvious,and the delamination damage on the surface of specimens is more serious.(3)The bearing capacity of carbon/glass hybrid composites specimens decreases after aging for 1344 hours.After aging for 1344 h,the bending strengths of carbon-glass hybrid composites specimens with the laying methods of[CCGG]_S,[GGCC]_S,[GCGC]_S and[CGCG]_S decrease by 14.9%,9.43%,6.83%and 8.90%,respectively.In the initial stage of bending damage,the AE signals with amplitude higher than 80 dB are generated by the aged specimen with laying methods of[CCGG]_S and[CGCG]_S,while the AE signals with amplitude lower than 60 dB are generated by the aged specimen with the laying methods of[GGCC]_S and[GCGC]_S.For aged and unaged specimens with double-layered carbon/glass hybrid,the number of AE signals generated during bending loading is approximately the same.For aged specimens with single-layered carbon-glass hybrid,the number of AE signals under bending loading is much lower than that of unaged specimens.(4)AE technology and DIC method are effective ways to study the bending deformation damage behaviors of composites after aging,and have guiding significance to ensure the long-term service and structural health monitoring of fiber reinforced composite structures in seawater environment.