本論文係針對長距離的管線做非破壞檢測時所使用的蘭姆波，研究其波傳特性及各式模態對缺陷之靈敏性評估。在平板型蘭姆波波傳中，經由理論推導，可發現存在對稱型波傳模態及反對稱型波傳模態。而圓柱管上的蘭姆波亦具有三種波傳模態，即縱向模態、扭力模態及撓曲模態。各型波傳模態，經由求解特徵方程式，可得各個模態之波速與頻率的關係。在實驗上，為應證頻散曲線中各模態波速隨頻率變化之關係，採用304不?袗?板及碳鋼圓柱管，以超音波探頭傾斜入射縱波以激振各式模態。當縱波在波傳介質上達到同相位之建設性干涉時，蘭姆波模態即可被激發出來。於實驗中，量測不同fd值下所激振蘭姆波模態之群波速度值，並將結果與數值理論值做比較分析，發現以此實驗架構方式，可有效的激振蘭姆波的模態產生。此外，在更進一步的研究中，將反應明顯的蘭姆波模態分別在具有缺陷之碳鋼圓柱管及不?袗?平板上，進行缺陷檢測，評估各種模態對缺陷之靈敏度及解析度。其結果顯示不同厚度及頻率之配合(不同fd值造成不同波傳能量分佈)將會對蘭姆波模態之檢測靈敏度及波形外觀造成波形混雜的結果。而利用激振單一模態以進行檢測，可使得回波訊號簡明易分析。另外，選用無頻散現象區域的模態對缺陷進行檢測，可以確保在波傳遞過程中，波形外觀保持一致性，而達到最小的衰減。此實驗量測結果將可作為利用蘭姆波檢測技術的參考依據。

This thesis studies Lamb waves for long-range pipeline inspection. The property of Lamb waves propagation and the sensitivity of defect detection will be evaluated in this thesis. There are two groups of waves propagation in plate, first group of waves are called symmetrical Lamb waves, and the second group are called anti-symmetrical Lamb waves. Furthermore, there are three different mode types exist in hollow cylinder, such as the longitudinal, torsional, and flexural modes. By solving the characteristic equation of the Lamb wave problem, the dispersion character of the Lamb waves can be found.

The phase and group velocity for different Lamb modes obtained from the dispersion curve are also studied in this thesis. In the experimental setup, the longitudinal wave is incident at certain incident angles and velocities to generate Lamb waves propagated on the stainless steel plate and carbon steel hollow cylinder. When the longitudinal waves are in the constructive interference in the medium, only one Lamb wave will propagate. As a result, compare with the measured data and theoretical predictions of the group velocities, it is observed that angle beam longitudinal waves offer an accurate and workable method for Lamb waves generation.

To evaluate the sensitivity and resolution of the Lamb waves testing, additional experiments for detecting defects are carried out in this thesis. It is found that a single and pure Lamb wave is very useful for detection defects. Moreover, selected the non-dispersive Lamb modes for detection can keep the propagating wave shape without changing; also, only minimum energy is decayed as wave propagated.

目 錄 I
表 目 錄 III
圖 目 錄 IV
中文摘要 XII
英文摘要 XIII
第一章 緒論 1
1.1 研究背景 1
1.2 文獻回顧 3
1.3 研究方法 6
第二章 理論分析 11
2.1 平板型蘭姆波 11
2.1.1 平板上蘭姆波波傳之特徵方程式 11
2.1.2 平板型蘭姆波之模態 15
2.1.3 平板型蘭姆波之相位速度與群波速度 17
2.2 圓柱管型蘭姆波 18
2.2.1 圓柱管型蘭姆波之特徵方程式 19
2.2.2 圓柱管型蘭姆波之模態 20
2.2.3 頻散曲線 22
2.2.4 波形結構 23
第三章 實驗架構及量測 28
3.1 平板上蘭姆波波傳量測實驗 29
3.1.1 實驗設備及檢測試片 30
3.1.2 平板型蘭姆波實驗之架構 32
3.2 圓柱管上蘭姆波波傳量測實驗 35
3.2.1 實驗設備及檢測試片 36
3.2.2 圓柱管型蘭姆波實驗量測 37
第四章 實驗結果與討論 49
4.1 平板型蘭姆波量測實驗 49
4.2 圓柱管型蘭姆波量測實驗 56
第五章 結論與建議 87
5.1 結論 87
5.2 建議 89
參考文獻 90
附錄A：圓柱管中波傳模態特徵方程式理論推導 93
附錄B：頻散曲線軟體計算程式 112
附錄C：實驗量測之蘭姆波模態回波訊號圖形 117
附錄D：各蘭姆波模態對缺陷之回波訊號圖形 122

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