采用超声导波阵列技术研究板类结构大面积检测

Guided wave arrays for large plate structures inspection

超声导波阵列检测技术可以实现板类结构的快速、大面积检测,是工业领域中最有前景的技术之一。针对目前此技术中存在的单一模态传感器难制作、检测频率高(一般在200 kHz以上)、需非常密集的传感器阵列和成像分辨率低等问题,本文采用一种圆环形线圈EMAT(Electromagnetic Acoustic Transducer),在较低频率15 kHz激励产生单一A0模态Lamb波,由8个传感器组成环形阵列,利用TFM(Total Focus Method)进行成像,实现了超声Lamb波对板类结构的快速、大面积检测。对一块包含直径为27 mm通孔的3 mm厚铝板进行实验研究,结果表明,此系统具有较高的测量稳定性和成像分辨率,能快速定位缺陷,适用于对板类结构进行大面积粗检。在对检测系统盲区形成原因分析的基础上,建立了一种计算盲区范围的方法。

Guided wave array provides a way to inspect large areas of plate-like structures quickly and has shown great potential in the industry. The problems with present methods to achieve this technology are that purity mode transducer is difficult to produce, operating frequency is high （usually above 200 kHz）, distance between transducers need to be small and image algorithm can＇t achieve the same resolution in all directions. In this paper the pancake coil EMAT （Electromagnetic Acoustic Transducer） is employed to produce purity A0 mode in 15 kHz. A circular array assembled by 8 EMATs and TFM（Total Focus Method） imaging algorithm are used to execute inspection. The validity and efficiency of the proposed method are demonstrated experimentally using a 3 mm thickness aluminum plate with a 27mm hole in the center. Results illustrate that the system can inspect large plate with high stability and imaging resolution. The reason for dead zone is studied and a model to calculate it is also established.