Development Of Acoustic Emission System And Research On Damage Monitoring Of Concrete

The damage of concrete structures will cause serious safety accidents,so long-term and real-time monitoring of concrete structures is of great significance.Among many monitoring technologies,acoustic emission technology,as a dynamic and real-time monitoring technology,is often used for damage monitoring of concrete structures because of its advantages of realtime,flexibility and high sensitivity.In the current research and application,most of the effective acoustic emission signals are extracted by commercial acoustic emission systems,and damage monitoring is realized by analyzing the characteristic parameters of the acoustic emission signals.However,commercial acoustic emission software has the problems of inability to expand relevant analysis algorithms and expensive.In addition,in experiments and engineering,commercial acoustic emission sensors are usually attached to the surface of the specimen or structure to ensure that the sensor can be reused.However,the high attenuation characteristics of the acoustic emission signal as it propagates in concrete results in distortion of the acoustic emission signal collected by the sensors attached to the surface.Finally,most of the existing studies use acoustic emission signals to qualitatively divide the evolution stages of concrete damage,and lack quantitative indicators for judging concrete damage.In view of the above problems,this paper firstly developed an acoustic emission acquisition and analysis system independently,and verified the accuracy of the system through experiments.Subsequently,qualitative and quantitative indicators reflecting concrete failure are proposed.The main research contents of the paper are as follows:(1)The acoustic emission acquisition and analysis system has been independently developed,which reduces the cost of using acoustic emission technology,and users can expand the programming by themselves.The acquisition,storage and analysis of acoustic emission signals are realized in the system,and the feasibility of the acquisition and analysis system is verified through the lead-breaking test.Through two-dimensional positioning experiments,the accuracy of the developed acoustic emission analysis system is proved.(2)The signals were collected by the developed acoustic emission system,and the characteristic parameters of acoustic emission were used to qualitatively divide the damage stage and identify the structural damage mechanism.Uniaxial loading tests of concrete standard cube specimens and four-point bending tests of reinforced concrete beam specimens were carried out.It is found that the damage stage can be qualitatively divided by the slope change of the cumulative ringing count curve,and the RA-AF value can effectively identify the shear failure of concrete beams.(3)The collected acoustic emission signals are further analyzed,and qualitative and quantitative indexes that can reflect the structural damage are proposed.Through the wavelet packet decomposition of the acoustic emission signal,the energy ratio of each frequency band when the concrete is loaded is extracted,and the qualitative index is proposed to reflect the damage law of the concrete structure.Based on the fractal dimension of acoustic emission intensity and the theory of acoustic emission b value,a quantitative index is proposed to effectively identify the damage degree of concrete structures.By comparing the indicators,it is found that the embedded sensor can more accurately reflect the damage and damage of the concrete structure because it avoids the attenuation of the signal when it propagates in the concrete,compared with the sticky sensor.