Study On Fatigue Crack Detection Method Of Steel Bridge Based On Acoustic Emission

Steel structure bridges are the main form of long-span bridges.They undertake the heavy task of crossing rivers,seas and canyons.Most of them are control projects of traffic lines.It is very important to ensure the safe operation of long-span steel bridges.Among the diseases of steel bridge structures,fatigue cracks are the most prone to occur and difficult to detect,which seriously threatens the safety of bridge operation.In view of the problems existing in the current steel bridge fatigue crack detection technology,this paper studies the application of acoustic emission technology to steel bridge fatigue crack detection,and achieves the following results:An experimental study is carried out on whether fatigue cracks are "active" and their state identification.A fatigue test of typical structural details of Q690 q steel is designed,the acoustic emission signal of the whole fatigue process is collected,and the signal change law during the fatigue process is explored.Wavelet transform is used to denoise the acoustic emission signal of fatigue crack,and the time domain,frequency domain and time-frequency domain characteristics of the acoustic emission signal in different damage stages of fatigue crack are studied by waveform analysis method.Extract various characteristic parameters for state identification of fatigue cracks in different damage stages,and then establish a new method for judging the fatigue crack state of steel bridge,which can be identified in the early stage of crack development and guide the maintenance of steel bridge.Aiming at the localization of fatigue cracks,an experimental study on the localization of damage sources was carried out.According to plate wave theory and acoustic emission source localization principle,the advantages and disadvantages of traditional time difference localization method and Morlet wavelet modal analysis localization method were compared in one-dimensional experiments.The method of wavelet modal analysis has more accurate positioning results.Furthermore,an optimization algorithm of hybrid Morlet wavelet modal analysis and Geiger algorithm is proposed,and the localization effect of Morlet wavelet modal analysis and hybrid algorithm is compared in two-dimensional experiments.The results show that the hybrid algorithm proposed in this paper can effectively improve positioning accuracy,more suitable for bridge site inspection.Based on the above research results,a full-life tracking detection method for fatigue cracks in steel bridges based on acoustic emission technology is proposed.The specimens whose fatigue cracks are detected continue to be loaded until they break,and the crosssection morphology is analyzed by scanning electron microscopy,which proves the method proposed in this paper.The state and location of fatigue cracks can be accurately identified.The detection experiment is carried out on the bridge test bench,which further verifies the effectiveness and applicability of the method proposed in this paper.