Research On Monitoring And Early Warning Parameters Of Steel Structures Fatigue Crack Propagation Based On Acoustic Emission

With the rapid development of modern industry,the transmission and communication tower use the metal material as its main material.And its quatity will be increase more than 10 thousands per year.Due to long-playing working in the natural environment,the tower is often affected by natural disasters,such as snow,ice,hurricanes,etc..Many researches found that the fatigue damage of steel structures is one of the main reasons for the collapse of the tower.And the fatigue damage of steel structure is a result of damage accumulation,which is very difficult to monitor by conventional nondestructive testing with static defects as the main objects.Using the acoustic emission technique we can monitor the fatigue crack propagation process of steel and effectively determine the damage in real time.In this work,we studied on the acoustic emission law of-Q345 B steel during fatigue crack growth is studied,which is mainly about:(1)Conduct fatigue crack propagation tests of different stress ratios(0.1、0.15、0.2).Based on study fatigue crack growth rate,not only verifies the accuracy of the test results,but also provides an effective and reliable mechanical basis for the study of the acoustic emission monitoring characteristics of fatigue crack propagation.(2)Study on acoustic emission parameters of fatigue crack propagation,Results show,the three stages of acoustic emission cumulative counting have a strong correspondence with the crack initiation stage,the stable growth stage and the unstable fracture stage of fatigue crack propagation,and the cumulative counting has the characteristics of early warning fatigue failure.(3)Based on the acoustic emission count rate for the material to enter the unstable fracture stage have the shortage of inconvenience identification,according to the characteristics of the cumulative count slope change in the second and the third stage,a new method is proposed to recognition the second and the third stages of fatigue crack propagation by using the discrete coefficient of acoustic emission count rate.According to the coefficient of dispersion of the counting rate in the second and the third stage of the cumulative count data will show different characteristics,which can provide the basis for the acoustic emission monitoring and early warning mode identification,can provide the basis for acoustic emission monitoring and early warning mode identification.(4)In order to reduce the amount of acoustic emission signal and white noise interference,and make the data-dealing easier and the reduced AE parameters can still be used for determinating the fatigue damage’s level,we introduced the average ringing count for a period of timeΔC/ΔN of single channel received AE signal as an early characteristic warning parameter.the average ringing count for a period of timeΔC/ΔN also recognition characteristic of the second and the third stages of fatigue crack propagation.This paper introduces two effective parameters for the identification of Q345 B steel fatigue crack growth into the third stage: coefficient of dispersion of the counting rate and the average ringing count for a period of timeΔC/ΔN,it is of great significance to identify and develop the equipment model based on acoustic emission monitoring tower fatigue fracture fault equipment.