| Fatigue is the main reason for the sudden failure of metal mechanical structure,which often leads to serious accidents and losses.Therefore,metal fatigue has long been the focus of engineering application and mechanical principle research.In the study of metal fatigue,because the fatigue micro damage stage has the characteristics of nonlinearity and small damage scale,it is difficult to measure the damage directly,so the indirect measurement method of nondestructive testing is often used.Nondestructive testing detects damage and defects by measuring the changes of physical quantities caused by material damage.It is widely used in the detection of fatigue damage.However,affected by the detection principle and low detectability of fatigue micro damage,most methods still have limitations in the detection of fatigue damage evolution.As a non-destructive testing method with high sensitivity and good real-time performance,acoustic emission testing can carry out the whole process and multi-scale dynamic detection of metal fatigue damage.How to characterize the fatigue evolution by using its dynamic monitoring characteristics in acoustic emission detection of metal fatigue? How to overcome the influence of noise on signal acquisition and analysis results? How to effectively deal with a large number of signals in detection? This is the focus of scholars’ research.For the above research problems,this paper puts forward three experimental schemes of metal fatigue detection,and studies the metal fatigue detection methods of acoustic emission from the aspects of signal noise reduction and data statistical processing.The main work includes:(1)In order to use the real-time performance of acoustic emission detection to evaluate the fatigue damage state on-line,the real-time and on-line acoustic emission detection of aluminum alloy 7075 fatigue damage is carried out in this paper.The experimental results show that the use of damper in on-line acoustic emission detection of metal fatigue will significantly reduce the noise amplitude,which provides a new idea for acoustic emission detection to avoid the influence of noise;Acoustic emission signal has no obvious evolution trend in the process of metal fatigue,but it increases significantly before fatigue failure,which can be used as an index to predict metal fatigue failure.(2)In order to explore whether the deterioration of the properties of metal materials caused by fatigue damage will be reflected in static tension,the experiments of static tension and acoustic emission of low carbon steel Q235 after fatigue were carried out.The experimental results show that the Kaiser effect is still obvious in static tension after metal fatigue,and it is also verified that the cumulative damage of metal fatigue will not be obviously reflected in a single load.(3)In order to characterize the fatigue damage degree and evolution of metal materials by acoustic emission,the data after passing the Kaiser effect point in the static tension of low carbon steel after fatigue were analyzed.The experimental results show that the acoustic emission signal parameters and statistical laws collected from static tension to failure show the regularity of changing with fatigue.This shows that the static tensile acoustic emission signal of metal materials after fatigue can evaluate the fatigue damage degree of materials.The research work of this paper defines the noise source of on-line acoustic emission detection of metal fatigue and puts forward the solution;The effectiveness of Kaiser effect after fatigue of metal materials is verified;The general law of tensile acoustic emission signal with fatigue evolution of low carbon steel after fatigue is obtained.The work of this paper provides a comprehensive reference for the experimental research of acoustic emission detection of metal fatigue. |
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