主動纖維複材的脫層偵測與驗證

Abstract

主動纖維複材是由一層直徑、長度相同的鋯鈦酸鉛纖維，以相同的方位整齊排列成一平面，再以環氧基樹脂填注於纖維之間，形成一片由壓電纖維與環氧基樹脂所構成的薄片，此薄片上下兩面各黏貼一片對稱排列之軟性指叉電極。這種材料具備了重量輕、可撓性、較佳的機電轉換性能、異向性靈敏度及韌性高的特性，能夠平順地與大型曲面的結構件結合在一起。 主動纖維複材黏貼在結構表面做為致動或信號偵測時，必須確保主動纖維複材與結構表面緊密結合，使其致動或感測能力確實無誤。本論文提出簡易、可靠的監測方法，以阻抗頻譜偵測主動纖維複材的黏貼狀況。黏貼在結構表面的主動纖維複材發生脫層時，脫離主結構的部分可視為單邊固定的懸臂板，此懸臂板的面內共振頻率與脫層尺寸相關。本研究將主動纖維複材與主結構的脫層分為脫層前緣與纖維垂直、平行及角落脫層三種情況進行探討。根據解析解、有限元素模擬與阻抗量測，確認面內的基本共振頻率與脫層大小成反比，並以電子光斑干涉證實脫層部分的共振為面內振動。此外，面內第二共振頻率與基本共振頻率的比值可用以辨識角落脫層前緣的走向。

This dissertation presents a novel method to monitor the bonding condition of active fiber composites (AFCs), which are formed with unidirectionally aligned piezoelectric fibers embedded in epoxy matrix and sandwiched between two symmetrical interdigital electrodes. Because of their mechanical flexibility and toughness, AFCs can be tailored to fit smoothly with curved shell structures and used as integrated sensors/actuators to compose functional structures. Delamination between AFC patch and host structure should be avoided and surveyed through its service life. AFC excited by sinusoidal voltage works like a resonator. Its electric charge is proportional to the strain field experienced by the host material integrated over its coverage area. The electric impedance and mechanical displacement of the AFC patch adhered on an aluminum plate were investigated in a broad frequency range. The modal characteristics depend on the size and shape of delamination. Three kinds of delaminations, including front edge, side edge and corner edge delaminations, were explored and discussed in this dissertation. Analytical solution, finite element simulation, impedance measurement and verification of in-plane vibration using electronic speckle pattern interferometry were presented to show the method for detection of active fiber composites is simple and reliable. Further, the frequency ratio of the second to the fundamental resonance of in-plane vibration plays a significant role to determine the orientation of corner edge delamination.