Study On Acoustic Emission Characteristics Damage And Aging Of FRP Sheets

The glass fiber reinforced plastics(FRP)has many advantages,such as high specific strength,large specific modulus,good electrical and thermal properties.It has been widely applied in petrochemical industry,construction industry,transportation industry,electronic communication industry and military industry.However,with the lengthening of the service life,the FRP is easy to aging,resulting in the deterioration of mechanical properties,cracks and fracture damage frequently.For the detection of the aging degree of composite materials,the common detection technology has some limitations.In this paper,the law of the propagation velocity of sound signal after aging of FRP is studied by acoustic emission(AE)technology.In combination with mechanical damage test,the relationship between the acoustic properties and mechanical properties of FRP is established.In this paper,the change law of the propagation velocity of sound signal after aging of FRP is studied by acoustic emission technology.In combination with mechanical damage test,the relationship between the acoustic properties of FRP and mechanical properties is established.This study is of great significance to the detection of aging and safety assessment of FRP equipment.In this paper,the research plan of acoustic emission characteristics damage and aging of FRP sheets was made from several aspects,such as test plate design,test plan design and test data analysis method.Then,the AE simulation experiments of 6 pieces of FRP plates with different structures were carried out for 234 times,and the propagation and amplitude attenuation rules of AE signals in different directions were obtained.The typical lead breaking signals were analyzed by wavelet and spectrum.The frequency range of the lead breaking signal was 31.25kHz~250kHz,and the signal was attenuated seriously during the propagation process.The greater the angle of the signal transmission and the angle of the fiber,the faster the amplitude of the signal voltage was attenuated.The attenuation speed was faster within 300mm,and then the decay rate gradually tends to be slow.On this basis,the tensile and flexural AE characteristics of 36 test samples were studied.Through analyzing the characteristic signals generated during the damage process of FRP sheets,the relationship between the mechanical model of the FRP with different structural types and the characteristic model of AE signals was established.The study found that there was a high degree of correlation between tensile load and AE amplitude of FRP with different fiber layers.The correlation degree was over 0.735,and the correlation degree between bending load and AE amplitude was more than 0.7.Therefore,the force condition of FRP and the fracture of the internal fiber can be judged by the amplitude of the signal.Based on the above research,4 periodic humid heat,irradiation accelerated aging and cross accelerating aging of 6 kinds of FRP specimens with 262 pieces were studied.Research suggested that after aging,the hardness of glass steel decreases,the tensile strength rises first and then decreases,the bending strength decreases as a whole,and the propagation speed of sound signal decreases.The propagation model of AE signals in the direction of[0~o],[45~o]and[90~o]along with the angle of fiber was established after the accelerated aging of humid heat and irradiation.Based on the grey correlation analysis,the correlation between the hardness of the plate and the bending strength,the sound velocity and the bending strength of all types of plates reached more than 0.7.The relationship between the sound velocity and mechanical properties of FRP sheets after aging was established.The aging degree of FRP materials and the decline of mechanical properties can be evaluated by the sound velocity measurement.