- 學位論文
鐵軌缺陷之超聲導波檢測：實驗研究
Ultrasonic Guided Wave Inspection for Rail Defects: Experimental Studies
摘要
傳統超音波探傷技術檢測鐵軌底部缺陷較軌頭或軌腹部位困難很多，本論文開發一LabVIEW程式將B掃描影像量測及正傳、背向散射導波譜圖計算程序予以優化，進行一系列方向濾波之超聲導波檢測鐵軌橫向缺陷的實驗，可以自B掃描影像及導波譜圖分離特定的導波模態。實驗採用空氣耦合超音波換能器在鐵軌上方進行線性掃描，以放電加工製作軌腹、軌座及軌趾的缺陷。置於軌頭表面的150 kHz接觸式音洩探頭能夠產生四種導波模態，簡單命名為A、B、C及D模態。A模態為軌頭模態，相速度接近雷利波波速。B、C、D模態響應在距離激發探頭24-48cm遠處，逐漸趨於穩定，缺陷散射模態則是能量消耗較少的C模態。背向散射導波所需的遠場距離因缺陷位置而增長，由短到長依序是軌底中央缺陷、軌腹缺陷、腳趾缺陷。參數研究所獲得的結果將有助於開發陣列空氣耦合超音波換能器。
並列摘要
Defect detection of rail bases is more difficult than heads and webs using conventional ultrasonic nondestructive testing techniques. This thesis conducts a series of guided wave experiments to detect transverse defects in rails using directional filter. A LabVIEW program has been implemented to optimize measuring B-scan images and determining the corresponding frequency spectra for forward propagating and backscattered guided waves. Any specific mode can be extracted from above-mentioned B-scan images or frequency spectra. An air-coupled ultrasonic transducer was used to detect guided wave signals through linear scanning over the rail, in which electric discharge machining discontinuities were separately manufactured at web, base, and toe. For brevity, four guided modes named as A to D were induced by a 150 kHz contact-type acoustic emission probe attached on the rail head. Mode A is the rail head mode with phase velocity close to the Rayleigh wave speed. The response of guided mode B, C, and D gradually becomes steady in a distance about 24-48 cm away from the surface-mounted transducer. The scattered mode is generally the mode C, which features weak attenuation. The guided mode backscattered from the defect requires longer far-field distance. The far-field distances increase in sequence for defects at the center of base, web, and toe. The results achieved by parameter study can be used to develop an array of air-coupled ultrasonic transducers for detection of rail defects.