Research On Ultrasonic Nondestructive Testing And Characterization Of Coating Properties

With the development of various types of coatings technology and its applications, in order to avoid or reduce the damage and loss of substrate caused by coating failure,researchers has paid more and more attention to testing and evaluation methods of coating properties. Ultrasonic nondestructive testing technology can achieve non-destructive, automated, simple and high efficiency detection,so that it can become an effective means of coating properties testing.On the basis of mastering the acoustic properties of coating and ultrasonic wave propagation law in coating,this paper studies the use of ultrasonic methods to nondestructive testing and characterization of coating thickness and its homogeneity,coating bond quality.For the detection problem of coating thickness and its homogeneity, we proposed the method for ultrasonic thickness measurement of coatings by Welch spectral estimation on the the basis of ultrasonic wave propagation law in coating. The relative errors between the evaluated and actual thickness are estimated less than 6%. On this basis, C # and Matlab mixed programming is used to integrate the thickness algorithm into C scan of scanning acoustic microscopy. Discrete color values is used to represent the coating thickness, the C scanning image of coating thickness distribution can be acquired.Then, we can achieve the purpose of the non-destructive evaluation of thickness homogeneity through image analysis.The detection and characterization problem of coating bond quality mainly includes coating bond defect detection and coating bond strength characterization. For coating bond defect, the bottom echo reflection method is used to detect artificial defect of coating bonding interface. For coating bond strength, we first use the bottom echo reflection and nonlinear ultrasonic techniques to measure the feature parameters sensitive to bond strength. Then, the ultrasonic nondestructive characterization of coating bond strength can achieve through establishing and analyzing the relationship between the characteristic parameters and bond strength measured by mechanical method.