| The heavy-duty gas turbine is the key science and technology of a country,which is related to energy,national defense security and industrial competitiveness.Its thermal barrier coating is internationally recognized as the core technology of heavy-duty gas turbine manufacturing.At present,there is a lack of effective non-destructive testing and evaluation technology and related instruments to support the basic scientific research of TBC for the heavy-duty gas turbine.Based on electro-magnetic ultrasonic testing and phased array technology,the structure of electro-magnetic phased array probe is designed to detect the substrate defects of the heavy-duty gas turbine by using the principle of three-coil system of array induction logging.Combined with the theory of elasticity,the ultrasonic detection model is designed to study the acoustic reflection characteristics of coating defects.The influence of interface flaws on the measurement signal is studied by reasonably designing the transmitting and receiving structure and parameters of electromagnetic phased array ultrasonic detection.It provides theoretical support for the subsequent detection of the interface flaws of the actual hot end blade.The main research contents and achievements include the following parts.The first part studies the application of induction logging in the detection of TBC thickness.The MATLAB program is written by using the calculation formulas of electromagnetic field distribution of horizontal coil system in three-layer medium of induction logging.This program is used to calculate and analyze the influences of coating thickness and substrate defect material change on electromagnetic field distribution characteristics.The coating thickness is 0.0004 m,and the conductivity of the substrate defect is 10~6S/m.The second part is the structure and parameter design of the electromagnetic ultrasonic phased array.Based on the principle of three-coil system of array induction logging,a new structure of electromagnetic phased array probe for detecting substrate defects is proposed.Through numerical calculation,it is determined that the array element spacing meets the requirements of scale factorαof 0.8074 and excitation frequency of 10 MHz,which can achieve the best electromagnetic detection of substrate defects.The problem of model design and mesh division in the research of millimeter scale small-scale curved surface elastic acoustic wave propagation is solved to calculate the influence of frequency,source and receiver position on the measured signal.The results show that the detection accuracy reaches 99.99%when the frequency is 200 k Hz,the transmitting source is facing the defect,and the relative position between the receiving and the defect is 0.005 m,which can effectively meet the requirements of heavy-duty gas turbine blade coating defect detection.The third part is the response characteristics analysis of the electromagnetic ultrasonic detection phased array.The optimal plane surface electromagnetic detection phased array model is used to detect substrate defects.The calculation formula of substrate defect size,position and spacing are summarized.The apparent conductivity amplitude of double-coil system and three-coil system is compared.The results show that the new method of three-coil system is obviously better than that of double-coil system.The results show that the response characteristics and the calculation formula of defect geometric parameters are basically consistent with the numerical simulation results of the plane surface electromagnetic detection model,which provides a theoretical basis for the subsequent detection of the actual thermal barrier coating substrate defects.The plane/curved surface ultrasonic detection model is used to detect coating defects,and the influence of defect size and thickness on the detection accuracy is numerically calculated.The results show that the minimum detectable coating defect size is 0.001m and thickness is 0.0015m of the model. |
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