碳纤维复合材料表面雷达吸波涂层超声测厚方法研究

Thickness Measurement of Radar Absorbing Coating on Carbon Fiber by Ultrasonic Method

针对碳纤维复合材料基底表面涂覆的雷达吸波涂层在超声测厚过程中由于涂层与基底间声阻抗接近导致界面回波信号弱,手动读取脉冲回波声程差时主观性强、效率低的问题,提出一种基于理论分析结合Matlab批量信号处理技术的涂层厚度测量方法。理论分析确定涂层上下表面回波信号的相位变化关系;采用Matlab脚本批量读取超声脉冲回波信号,并手动选取涂层上下表面回波信号的波峰(谷)所处时域范围,脚本寻找波峰(谷)位置并计算回波声程差;结合超声波在涂层中传播速度计算涂层厚度。利用该方法对碳纤维复合材料基底表面的2种雷达吸波涂层进行厚度测量,结果表明:该方法在满足测厚精度要求的同时,能有效解决手动读取脉冲回波声程差时主观性强、效率低的问题,具有较好的工程化应用前景。

Due to the close acoustic impedance of radar absorbing coating(RAC)and carbon fiber substrate,the ultrasonic echo signal is too weak to be recognized accurately by the ultrasonic thickness measurement software,and recognizing pulse echo acoustic path difference manually is subjective and inefficient.To solve this problem,a coating thickness measurement method based on theoretical analysis combined with Matlab batch signal processing technology was proposed.Firstly,the phase change relationship of the echo signals on the upper and lower surfaces of the coating was determined by theoretical analysis.Then,the ultrasonic pulse echo signals were read in batch by Matlab script,and the time domain range of the peak(valley)of the echo signals on the upper and lower surfaces of the coating was manually selected.The position of the peak(valley)was confirmed by the script,and the echo acoustic path difference was calculated.Finally,the thickness of the coating was calculated based on the propagation rate of the ultrasonic wave in the coating.The thicknesses of two kinds of radar absorbing coatings on carbon fiber substrate were measured by this method.The results show that this method can not only meet the requirement of thickness measurement accuracy,but effectively solve the problems of subjectivity and low efficiency when recognizing the pulse echo path difference manually,so it has a good prospect of engineering application.