Generating Guided Waves in Isotropic Plates for Defect Detection with a Bulk Shear Wave Transducer

橫波直探頭在各向同性板中激勵超聲導波進行缺陷檢測的研究

張學聰(Xuecong Zhang) ； 何存富(Cunfu He) ； 呂炎(Yan Lu) ； 吳斌(Bin Wu)

《中國機械工程學刊》 38卷6期 (2017/12) Pp. 683-694

摘要

Bulk shear wave (BSW) transducers are usually used to generate bulk shear waves to detect defects. In the study, we generated guided waves in a steel plate for defect detection with a BSW transducer. A 0.5- MHz BSW transducer was coupled on a steel plate (1200 mm×610 mm×0.2 mm) with a couplant. We firstly identified the generated wave modes and then experimentally validated the propagation directions. The guided waves were classified into Lamb waves (S_0 and A_0 modes) and shear horizontal waves (SH_0 mode) and the primary modes were S_0 and SH_0 propagating in two perpendicular directions. In this way, rectangular through-thickness notches with the orientations of 0° and 90° in the plate were detected by S_0 and SH_0 modes with a BSW transducer. The results validated that the S_0 mode or SH_0 mode might be used to detect the defects by turning the BSW transducer and that the BSW transducer could excite SH_0 mode to detect rectangular cracks of 0° and 90° and excite S_0 mode to detect the cracks of 0°. The study provided a fast and convenient method to generate Lamb and SH waves for defect detection.

關鍵字

ultrasonic guided wave ； bulk shear wave transducer ； mode identification ； defect detection

並列摘要

橫波直探頭經常用於產生剪切體波進行缺陷檢測。本研究中，以橫波直探頭在鋼板中產生超聲導波來進行缺陷檢測。一個0.5MHz的橫波直探頭通過耦合劑耦合在一塊1200mm×610mm的鋼板上，首先通過實驗識別了產生出的模態，並證明了他們的傳播方向：產生的超聲導波為蘭姆波(S_0和A_0模態)和水準剪切波(SH_0模態)，並且主要的模態為在互相垂直的兩個方向上傳播的S_0模態和SH_0模態。在此基礎上，用橫波直探頭激勵出的S_0模態和SH_0模態檢測了偏轉角為0°和90°的矩形通透缺陷。結果表明，通過轉動橫波直探頭可以選擇S_0模態或SH_0模態以檢測缺陷，並且橫波直探頭可激勵SH_0模態檢測0°和90°的缺陷，激勵S_0模態檢測0°的缺陷。本研究提供了一種快速且方便地產生蘭姆波和水準剪切波，用以缺陷檢測的方法。