管道结构中的类兰姆波层析成像

理论和实验上研究了层析成像在管道结构导波检测中的适用性。在管的两个圆周带上分别布置发射和接收换能器,形成多点发射-多点接收的几何结构。将管中绕管道沿最短路径的螺旋方向到达接收换能器的模式作为感兴趣的模式,它们看起来像在弯曲的板中传播,称之为类兰姆波模式。给出了类兰姆波各射线路径走时的理论计算方法,并采用联合迭代重建技术(SIRT)对走时数据进行慢度图像重建。数值模拟和实验研究了管中横穿孔缺陷层析成像的输出并对健康管和缺陷管中类兰姆波的走时数据进行比较,发现穿过缺陷区域的类兰姆波因为绕过缺陷传播而呈现出更长的走时。文中也给出了两缺陷管道类兰姆波层析成像的数值模拟和实验结果,相比单缺陷的情况,射线较少穿过区域缺陷的重建图像质量下降。研究结果为采用类兰姆波模式进行管道缺陷无损评价提供了理论依据。 

Lamb-like wave tomography of pipe structures

The adapation of the tomographic reconstruction to the guided wave inspection of pipe structures is investigated theoretically and experimentally.The geometry is formed in multiple pitch-catch configurations when transmits and receivers are respectively laid along two parallel circumferential belts around the pipe.Among the various guided wave modes propagating in pipe,it is those called Lamb-like modes that are of the interest in our investigation.These modes see the pipe more like a curved plate and take the helical direction of the shortest path around the pipe to the receiving transducer.The method calculating the arrival times of ray paths of Lamb-like waves is theoretically given, and the simultaneous iterative reconstruction technique(SIRT) is carried out to realize slowness imaging reconstruction for the given set of arrival times.Reconstruction for both numerical and experimental data acquired on pipes with through hole Haws is presented,and the arrival times of Lamb-like waves in healthy and damaged pipe are extracted and compared,it is found that Lamb waves that pass through the flaw zone indicate different arrival time information.This shows up as a longer arrival time because the guided waves tend to skirt around the flaw.Lamb-like wave tomographic reconstructions of pipes with two flaws are also demonstrated numerically and experimentally.Compared to the case of single flaw,reconstructed image quality of the flaw where fewer rays go through degrades.These results provide a theoretical basis for quantitative nondestructive evaluation of pipe damage using Lamb-like wave tomography.