A Nondestructive Testing Method Research Based On Electro-thermo-acoustic Effect

The material properties of metallic and nonmetallic components may change after longtime service.In the worst cases,the failure of the components could lead to equipment accidents.It is great significance to evaluate the material state of each component to ensure the normal operation.Nondestructive testing(NDT)plays an important role in ensuring the smooth operation of equipment and improving the performance of products.The paper proposes a new NDT methods based on thermos-acoustic effect by studying thermos-acoustic properties of metallic materials,and designs an on-line / off-line detection system.Compared with regular NDT methods,Detection method based on electro-thermal-acoustic effect has advantages such as noncontact,fast,well operation,easy to setup and befitting for real-time detection.In this thesis,an new NDT method is demonstrated based on electro-thermal-acoustic effect.Firstly,this paper analyzes the conversion mechanism of electro-thermo-acoustic effect and calculates the plate thermoacoustic model.Sound pressure expression caused by Joule heating in general condition is generated.In addition,theoretical deduce on a thermoacoustic coupling model with multilayer structure is conducted.A numerial simulation considering material properties is carried out,and the relationship between thermoacoustic pressure and material properties is obtained.Secondly,electro-thermal-acoustic coupling simulation for metal materials is studied by using the finite element method.The distribution of temperature field and the sound field around the metal specimen are obtained respectively,which verified the feasibility for electro-thermo-acoustic conversion of multilayer structures.Meanwhile,the influence on thermoacoustic characteristics owing to changes of electromagnetic parameters and specimen's structural state is studied by simulation software,which provides a theoretical basis for the subsequent experimental research.Thirdly,the paper designs electro-thermal-acoustic detection system based on theoretical research and simulation analysis,including hardware design or selection and software development.The hardware structure are configured to satisfy NDT requirements,including signal generator,amplifier,microphone and signal acquisition card,while focus on designing the power amplifier and arranging sensors.Moreover,a detection control software is developed based on LabVIEW.The software consist of parameters input unit,waveform analysis,acquisition control unit and data graphic display unit.It has the basic functions of data acquisition,control,data storage and playback,signal feature extraction,filtering and frequency spectrum analysis.Finally,two actual specimens,including metal with surface tension deformation and metal with heat treatment,were tested on software system based on the proposed method.The relationship between thermoacoustic signal and metal material is studied,the result has good agreement with the simulation analysis,which verifies the feasibility of electro-thermal-acoustic detection method.The detection method presented in this paper can meet the needs of NDT of material status.The proposed method based on electro-thermal-acoustic effect can detect the changes of material properties effectively,which provides a feasible idea for the research on portable online NDT equipment with a wide application prospect.