| With the rapid development of aerospace technology in China,the performance requirements for aircraft engines are increasingly increasing.In order to improve engine performance,it is necessary to increase the combustion chamber temperature to improve the thermal efficiency and thrust weight ratio of the engine.Engine blades face a very severe high-temperature test.As an advanced thermal protection technology,thermal barrier coating technology plays an important role in protecting engine blades.The thermal barrier coating structure is a double layer,with the surface layer being a ceramic topcoat and the bottom layer being a bond coat.The thermal insulation performance of the ceramic topcoat is closely related to the service life and reliability of the blade,and it is necessary to measure its thickness to ensure thermal insulation performance.Eddy current method is commonly used for coating thickness measurement due to its non-destructive and high detection efficiency.There is a coupling relationship between the thickness of the bond coat and the thickness of the ceramic topcoat which affects the thickness measurement accuracy of the ceramic topcoat.Currently,most commercial eddy current coating thickness testers are only suitable for measuring the thickness of single layer non-conductive coatings and cannot be used for measuring the thickness of ceramic topcoats of thermal barrier coatings.Based on the basic theory of eddy current thickness measurement,finite element modeling and simulation,thickness measurement system development and experimental demonstration,this thesis conducts in-depth research on the ceramic topcoat thickness measurement system.The main work is as follows:1.Construction of finite element model for ceramic topcoat thickness measurement.Based on the transformer model,eddy current thickness measurement principle and finite element model construction theory,establishing a finite element model for eddy current thickness measurement of ceramic topcoats using COMSOL.The correctness of the constructed model is verified using the harmonic eddy current field integral analytical model of double-layer conductors,further,optimize the structural parameters of the thickness measuring coil based on the finite element model.2.Research on thickness measurement method of ceramic topcoat.The relationship between the coil quality factor and the thickness of the ceramic topcoat is derived based on the transformer model and the mapping relationship between the two was established using the S-curve.The effects of excitation frequency,bond coat thickness of calibration specimen,substrate thickness on thickness measurement of ceramic topcoat were analyzed.Based on the above analysis,a compensation method is proposed to suppress the impact of changes in the thickness of the bond coat on the thickness measurement of the ceramic topcoat.3.Development of ceramic topcoat thickness measurement system.According to the coil quality factor extraction requirements and post processing methods,the thickness measurement system is developed from both embedded hardware and software.In terms of hardware,with the Wheatstone bridge and AD8302 as the core,a hardware system framework is constructed and chips in various parts of the framework are selected to design reasonable chip peripheral circuits.In terms of software,using GD32,we wrote chip control programs and thickness measurement programs,and designed a thickness measurement APP that cooperates with GD32 to achieve complete thickness measurement functions.4.System experiments and performance evaluation.Nine thermal barrier coating specimens were prepared and the thickness of the ceramic topcoats were measured using the established thickness measurement system.The thickness measurement errors using different methods,frequencies and coils were analyzed,as well as the thickness measurement errors before and after compensation using the S-curve method.Evaluate the signal to noise ratio,stability,signal quality,resolution,and other indicators of the thickness measurement system.The results show that the system has high signal-tonoise ratio and stability and the relative error of thickness measurement before compensation is less than 4.75%,while the relative error of thickness measurement after compensation is less than 2.78%.The research conducted in this thesis is dedicated to achieving efficient and highprecision measurement of ceramic topcoat thickness.The proposed ceramic topcoat thickness compensation algorithm reduces thickness measurement errors as a whole,providing an effective solution for eddy current thickness measurement of ceramic topcoat.This thesis contains 93 figures,21 tables and 118 references. |
