壓電陶瓷纖維複材平板導波特性的實驗及數值分析

Abstract

壓電陶瓷纖維複材是由相同方向排列的壓電纖維、環氧樹脂及兩層聚醯亞胺所構成的三明治結構。原本抗拉性差的壓電纖維埋入環氧樹脂，後者分擔張應力，使壓電纖維複材具有可撓性，又不失其主動性能。本研究以實驗及數值分析未極化之壓電陶瓷纖維複材的板波波傳，瞭解纖維排列方向對於板波頻散特性的影響。採用Nd:YAG脈衝雷射為板波激發源，壓力波及剪力波探頭感測板波，以步進馬達驅動之光學平台沿波傳方向線性掃描，將多筆單點時域訊號排列成時間與空間域的B掃描灰階圖，以二維快速傅立葉轉換獲得導波頻散曲線。數值模擬採用有限元素法套裝軟體，分析板波在壓電陶瓷纖維複材平板的頻散特性及自然模態。在不平行於纖維的波傳方向上，沒有純粹的矢面波及水平偏極波，準矢面板波與準水平偏極板波都具有特定的位移偏振角。數值模擬及實驗結果顯示，剪力波探頭具備同時量測任意波傳方向之板波頻散曲線的能力。

Piezoelectric fiber composites are made of unidirectional piezoelectric ceramic fibers embedded in epoxy resin and sandwiched between two polyimide films. With assistance of the extensible epoxy resin, the originally brittle piezoelectric ceramic fibers become flexible and have no loss of active ability. This thesis experimentally and numerically studies plate wave propagation in a non-poled piezoelectric fiber composite to understand fiber orientation depending dispersive characteristics. A Nd:YAG pulsed laser was used to stimulate plate waves. The point sources separated by a constant interval were linearly scanned by a stepper driving optical stage in the wave propagating direction. The B-scan data captured by a pressure wave transducer or a shear wave transducer were arranged in time and space domain. Dispersion spectra were achieved by a two-dimensional fast Fourier transform. The dispersive characteristics and modal deformations of plate waves in the piezoelectric fiber composite were also determined by use of a commercial finite-element code. There are neither pure sagittal plate waves nor transverse horizontal (TH) plate waves in off-axis propagation. Specific polarization angle can be discovered in the quasi-sagittal plate wave and quasi-TH plate wave. Numerical and experimental evidence indicates that shear wave transducers are capable of measuring dispersion curves for plate wave propagation in arbitrary directions.