基于激光超声C扫描测量加强筋宽度的方法

Method of Measuring the Width of Stiffeners by Using Laser Ultrasonic C-Scan

为了对加强筋宽度进行在役、快速、非接触、无损测量,提出了一种激光超声C扫描测量方法。首先,通过建模和理论计算,分析了脉冲激光在2 mm厚304不锈钢板上激励的超声场分布情况;然后,通过激光超声实验得到304不锈钢板中的超声场分布,并与理论计算结果进行对比;最后,采用激光超声C扫描测量加强筋的宽度,并用小波降噪和图像均值滤波方法对图像进行处理。实验结果表明,当激励点与接收点的距离为4 mm时,脉冲激光在304不锈钢板上激励的反射横波幅值高于纵波幅值。将反射横波幅值作为特征信号对304不锈钢板上的加强筋进行激光超声C扫描测量,结果表明,从图像中获取的加强筋宽度和实际宽度的绝对误差小于0.05 mm,满足工程检测的误差要求。

In order to measure the width of stiffener in service,fast,contactless and non-destructive,a laser ultrasonic C-scan measurement method is proposed in this work.First,the ultrasonic wave field induced by a pulsed laser excited at a 2 mm-thick 304 stainless steel plate is studied by modelling and theoretical calculation.Then,the ultrasonic field distribution in the 304 stainless steel plate is obtained by laser ultrasonic experiments,and the results are compared with theoretical calculation.Finally,the laser ultrasonic C-scan is used to measure the width of the stiffeners,and the images are processed by the wavelet denoising and image averaging filtering methods.Experimental results show that the amplitude of the reflected transverse wave excited by the pulsed laser on the 304 stainless steel plate is higher than that of the longitudinal wave when the receiving point is 4 mm away from the exciting point.Using the reflected transverse wave amplitude as the characteristic signal,the laser ultrasonic C-scan measurement is performed on the stiffeners on the 304 stainless steel plate,and the absolute error between the width of stiffener obtained from the image and the actual width is less than 0.05 mm,which meets the error requirements of engineering inspection.