Research On Non-Destructive Testing(Monitoring)and Intelligent Evaluation Technology Of Bolt Corrosion In Coal Mine

As a support method widely used in coal mines,bolt support has been paid more and more attention when coal mining in our country is developing to depth day by day.However,metal bolts in coal mines face the effects of high temperature,high humidity and high stress for a long time in the process of underground service.extremely prone to corrosion.By using the methods of theoretical analysis and consulting literature,this thesis makes an in-depth analysis of the corrosion type and mechanism of coal mine anchor,as well as the principles and characteristics of semi-cell potential method,linear polarization method and ultrasonic guided wave testing.Copper accelerated acetate salt spray test was used to accelerate the corrosion of anchor,the change of corrosion potential was recorded,and the change of corrosion rate of anchor was measured by potentiostat.The anchor after accelerated corrosion is dried to remove rust,the actual corrosion quality loss is calculated and compared with the theoretical corrosion quality loss measured by linear polarization method,and the tensile test is carried out on the corroded anchor.the effects of corrosion time and mass loss rate on the mechanical properties of anchor were studied.Using MATLAB software,the propagation characteristics of guided wave in bolt are calculated,and the dispersion curve is drawn;using ANSYS finite element software,the ultrasonic guided wave detection of anchor length and corrosion defect location is simulated;finally,the bolt corrosion monitoring(inspection)technology and corrosion evaluation method are designed.The main research results are as follows:(1)In the process of anchor corrosion,there are four stages of potential in the corrosion process,the first stage is in the first day,the second stage is in the 2 ～ 7 days,the third stage is in the 7 ～ 21 days,and the fourth stage is after 21 days.The corrosion rate of anchor also follows this law.In the second stage,the corrosion rate is the highest,the corrosion rate decreases in the third stage,and tends to be stable in the fourth stage.(2)The linear polarization method can accurately measure the corrosion rate of the bolt,and the mechanical properties of the bolt decrease linearly with the increase of the mass loss of the bolt,so the corrosion of the bolt can be detected and monitored by electrochemical method.(3)The Pochhammer equation of longitudinal guided wave propagation in the rod is derived,and the dispersion characteristic curve of guided wave propagation in bolt and anchor solid is drawn.The appropriate excitation signal frequency is selected according to the dispersion curve,and the numerical simulation is carried out in ANSYS.The results show that ultrasonic guided wave is reliable in monitoring anchor length and corrosion defect location.(4)The corrosion potential-corrosion current density regression model is established,the anchor corrosion monitoring and detection process is designed,and the calculation method of corrosion potential-corrosion current density regression model based on gradient descent method is determined.the workload of solving the regression equation is reduced,the corrosion evaluation standard based on corrosion rate is designed,and different treatment suggestions are put forward according to different corrosion levels.The thesis has 41 pictures,9 tables,and 71 references.