Research On Damage Location Method Based On Acoustic Emission Signal And Its Application

As a dynamic nondestructive testing technology,acoustic emission technology plays an important role in fault diagnosis and structural health monitoring.It has been widely used in practical engineering.When the stress inside the material exceeds the yield limit of the material and the material goes into the plastic deformation stage and generates damage defects,the stress wave will be released in the form of strain energy,the stress wave is the acoustic emission wave.Acoustic emission source location is an important aspect of acoustic emission technology.The position of acoustic emission source is the location of damage of material.The accurate location of acoustic emission source can help to evaluate the damage degree of material accurately.Acoustic emission signal contains a lot of information above material damage.It is a kind of non-stationary and complex transient signal.The reasonable processing and analysis of acoustic emission signal is a prerequisite for analyzing the damage degree of materials and assessing structure health.In the thesis,the basic concepts of acoustic emission technology,acoustic emission source localization method are introduced.With the rock material as the background,the de-noising and time-estimation analysis of acoustic emission signals are mainly studied.The source location method of single medium and two-layer medium,positioning result correction method and its application in rock materials are also discussed.The main research contents are:(1)In the traditional wavelet threshold de-noising,the wavelet coefficients are not continuous at the threshold after denoising by the soft threshold function and the wavelet coefficients have a constant deviation from the original wavelet coefficients after the soft threshold function denoising.The thesis studies the denoising method by using the sigmoid function as threshold function,and compares the de noising effect with soft and hart threshold function.Aiming at the non-stationary characteristic of acoustic emission signal and the problem that the acoustic emission signal contains a large amount of noise,a mathematic model of the arrival time estimation is established.From the perspective of probability and statistics,the method of arrival time estimation is studied based on probability density function.The effectiveness of the method is verified by the measured AE signals.(2)The structure of the two-layer medium is often encountered in the project.A mathematic model of source localization of the two-layer medium is established.Aiming at the problem of slow convergence and low positioning accuracy of conventional acoustic emission sources location method.The feasibility of using the PSO algorithm to locate acoustic emission sources is studied.The method of particle swarm localization can effectively avoid the problem of location inaccuracies caused by the singularity of matrix coefficients of linear equations in Geiger method.Then,the exact solution of acoustic emission source is calculated by PSO algorithm.The acoustic emission data of the uniaxial compression experiment and the lead-break experiment are used to verify the effectiveness of the method.(3)The uniaxial compression experiment and the lead-break experiment of rock materials with different materials and different specifications are carried out.The method of signal denoising,time estimation and acoustic emission source location in rock materials are validated.The sound wave velocity can't be measured accurately and the time delay estimation always has deviation.And the velocity and time delay estimation have a great influence on the location accuracy of the acoustic emission source.So the BP neural network is used to correct the source location result with velocity perturbation and the time arrival perturbation.And the correct method based on BP neural network turned out to be effective.The research of this thesis has important theoretical significance for the processing and analysis of acoustic emission signals and the accurate positioning of acoustic emission sources.It is of great practical significance to determine the position and damage degree of materials,evaluate the health of the structure and predict the service life of the structure.It is of great practical significance to promote the application of acoustic emission detection technology.