板波波傳為基礎之複材層板結構健康監測研究

Abstract

本文探討以窄頻板波波傳為基礎之複材結構健康監測的工作原理。以圓碟形壓電陶瓷元件為板波生成的致動器與感測器，布建於複材層板表面，構成主動偵測缺陷散射波之陣列。複材層板為非等向性結構，板波特性與波傳方向及頻率相關。本研究以雷射超音波技術與二維快速傅立葉轉換，量測板波相速度頻散曲線，反算複材試片的材料勁度係數，再正算板波群速度、波程時間。根據小波轉換獲得之散射波波程時間資料，以簡單體法尋優程序計算散射波源位置，目標函數具有全域單一極小值。以黏貼於試片表面的同質壓電陶瓷碟片作為模擬缺陷散射波的致動器，自壓電碟片邊緣生成散射板波，其波傳行為與缺陷產生的散射波近似。散射波源定位計算結果與實驗配置吻合，誤差小於壓電碟片的半徑。

This thesis studies the structural health monitoring principles for composite laminates based on propagation of narrowed-band plate waves. A number of piezoelectric, ceramic discs surface mounted on the composite laminates are used to be actuators and sensors in sequence for plate wave generation and detection and construct an active monitoring array. The propagation of plate waves in composite laminates is inherently complex due to their dispersion and anisotropy properties. An experimental technique based on laser-induced ultrasound and 2D fast Fourier transform was used to measure phase velocities of plate waves in a broad frequency range. The stiffness constants of the plate specimens determined by an inverse scheme are further used to evaluate the group velocities and times-of-flight of wave packets. An optimization scheme based on the time-of-flight data calculated through wavelet transform of scattering waves is established for source location of the defects using simplex method. The simulated scattering waves are launched from edges of the piezoelectric discs and approximate to the real waves scattered from defects. The objective function contains only a single global minimum. The source location results are in very good agreement with the actual experimental setup with errors less than radius of the piezoelectric discs.