臺灣博碩士論文加值系統

楔形體導波(Wedge Wave, WW)為一沿著楔形體尖端傳遞的一種彈性波，其能量聚集在楔形體尖端至一個波長範圍內。根據研究，當楔形體在頂端無截平(Truncation)之情形下，則不會具備隨頻率而改變其對應速度的頻散關係(Dispersion)。在過去的文獻對楔形體導波已有許多相關的研究，無論是在幾合外型上、鍍膜狀態、邊界條件負載以及單一缺陷深寬之影響，然而將楔形體結合聲子晶體之研究尚未有人進行探討，因此本文將對其進行探討。聲子晶體(Phononic Crystal)，為光子晶體(Photonic Crystal)所延伸之研究，其特性為當聲波通過一週期性排列結構時，聲波會因此結構之緣故造成穿透波及反射波的干擾發生頻溝現象(Band Gap)，即阻絕某些頻率震盪之聲波通過。
本研究分為兩部分，分別為實際實驗與有限元素分析法探討楔形體頂端具有規則週期性缺陷的波傳行為，探討不同的缺陷參數變化對於楔形體導波的影響。研究中以頂角角度為60°之黃銅楔形體作為基材試片，於尖端處設計不同之缺陷長度，且每一試片缺陷間距離的比例皆為1:1，藉由雷射超音波量測技術，觀察楔形體導波傳遞於規則缺陷試片時發生的波傳行為；在有限元素分析方面模擬實際情況進行動態分析。取得實驗及數值分析的時域訊號後，配合快速傅立葉快速轉換(Fast Fourier Transform, FFT)之訊號處理得到結果進行比對。
本研究成功利用雷射超音波量測技術及有限元素分析探討規則缺陷對些楔體導播之影響，雖研究結果無法觀察出聲子晶體之頻溝現象，但就實驗結果中發現不同規則週期性缺陷之楔形體導波的頻域訊號會因缺陷的間隔越大或個數的增加，導致主頻移頻且有規律遞減之趨勢，也應證了利用有限元素分析配合雷射超音波實驗能完整呈現楔形體導波波傳行為，進而精準的推算出楔形體導波經過規則缺陷後，頻域表現下主頻降頻之現象。

Wedge Wave (WW) is a kind of elastic wave propagate along the tip of a wedge that energy is concentrated near wedge tip to in 1 wavelength. According to the study, when the wedge tip has no truncation, there is no dispersion relationship that changes its corresponding velocity with frequency. In the literatures have been many related studies on wedge-shaped guided waves, However, the study of combining wedges with phononic crystals has not yet been studied. Therefore, this article will explore it. Phononic Crystal, a study extended by Photonic Crystal, is characterized in that when sound waves pass through a periodic arrangement structure, the acoustic wave will cause interference of the penetrating wave and the reflected wave due to the structure. We call this Band Gap, which blocks the passage of acoustic wave with certain frequency oscillations.
This study is divided into two parts, experimental measurement and finite element analysis method are used to investigate the wave propagation behavior of regular periodic defects at wedge tip, and to explore the influence of different periodic defect parameter changes on the guided wave of the wedge body. In this study, a brass wedge with a apex angle of 60° was used as the substrate test piece, the periodic defects were designed at the wedge tips, the ratio of the defects width and spacing width was 1:1,.Explore its influence after obtaining the frequency-domain by laser ultrasonic technique and finite element analysis.
Laser ultrasonic technique and finite element analysis were used to investigate the influence of periodic defects on wedges, although the results couldn’t be observed band gap. However, in the experimental results, it is found that the frequency domain signals would be effected by periodic defects on wedge tips, basic frequency would be downgraded by increase in defect width or increase in number of defects.

目 錄
中文摘要 i
英文摘要 iii
誌 謝 iv
目 錄 v
表目錄 vii
圖目錄 viii
第一章 緒論 1
1.1 前言 1
1.2 文獻回顧 2
1.3 研究目的 5
第二章 實驗量測 6
2.1 實驗試片 7
2.1.1楔形體材料 8
2.1.2頂角角度 8
2.1.3缺陷深度(H)、寬度(W)與排列 8
2.1.4試片編號 9
2.1.5試片準備 9
2.2 實驗架設 11
2.2.1截平現象實驗 12
2.2.2楔形體導波波傳實驗 15
2.3雷射超音波技術 17
2.3.1雷射超音波激發系統 18
2.3.2雷射超音波接收技統 20
第三章 有限元素分析 22
3.1 分析程序 23
3.1.1模型建立 24
3.1.2材料性質設定 26
3.1.3分析方法選擇 26
3.1.4邊界條件及外部負載設定 29
3.1.5網格分割 30
第四章 結果與討論 35
4.1 收斂性測試 35
4.2 實驗結果 37
4.2.1具3個規則排列缺陷之楔形體 37
4.2.2具4個規則排列缺陷之楔形體 41
4.2.3不同缺陷之實驗訊號比較 42
4.3 有限元素分析結果 45
4.3.1具3個規則排列缺陷之楔形體 46
4.3.2具4個規則排列缺陷之楔形體 48
4.3.3不同缺陷之模擬訊號比較 49
4.4 實驗與分析結果比對 52
第五章 結論 57
參考文獻 59

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