撓性壓電纖維複材換能器應用於複材脫層缺陷的導波檢測

Abstract

纖維補強複材結構成品缺陷主要為脫膠或脫層，本文應用實驗室已開發的具反對稱指叉電極之撓性壓電複材導波換能器(簡稱AE-PFC )，檢測在厚度變化處具有缺陷之玻璃纖維複材平板。本研究先以雷射超音波技術激發玻纖複材板內的寬頻板波，應用二維快速傅立葉轉換(2D-FFT)求出頻散曲線實驗解，再以粒子群演算法反算材料係數，建立此複合材料平板的理論解。以變化頻率時諧激發的方式量測板波頻率響應，寬頻脈衝激發搭配2D-FFT分析其激發的蘭姆波模態，探討AE-PFC在編織玻纖複材層板之A0及S0模態個別的機械頻率響應。考量波傳距離及板波模態的應用，本研究採用設計波長3.2 mm之AE-PFC於四層玻纖複材板的適當操作頻率為130 kHz (A0模態)及480 kHz (S0模態)。最後以AE-PFC作為蘭姆波的激發源，搭配線性掃描技術對脫層及厚度變化進行檢測，使用方向濾波器對感測到的時域訊號進行分析。結果顯示A0模態對於對稱脫層有反應，S0模態則否；A0及S0模態皆對厚度變化處無反應；量測厚度變化處含有損傷的試片，S0模態會有明顯的反射訊號，可作為判斷損傷的依據。

De-bonds and delamination are frequently found in fiber-reinforced composite laminate products, especially in varying thickness regions. This thesis explores guided wave detection of delamination in woven glass-epoxy composites using laboratory developed flexible piezoelectric fiber composite transducers with anti-symmetric interdigitated electrodes (abbreviated as AE-PFC). Elastic constants of the composite laminate were determined by an inverse scheme based on particle swarm optimization through the measured dispersion curves of Lamb waves. Theoretical solution of wave propagation in the composite plate is established with these material constants. The excitations of A0 and S0 modes were investigated by tone-burst of swept frequency and short pulse with the aid of 2D-FFT processing. A number of AE-PFC transducers with designed wavelength of 3.2 mm were used to inspect four-ply glass-epoxy laminates. The A0 and S0 modes can be excited at 130 kHz and 480 kHz, respectively. For inspection of delamination and that in the composites of varying thickness, the individual Lamb mode was launched by AE-PFC and captured by a linear scan configuration. The forward propagating and back scattered B-scan images were decomposed by a temporal-spatial direction filter. Experimental results reveal that A0 modes are sensitive to symmetric delamination, S0 modes are not. Both A0 and S0 mode are non-sensitive to thickness changes. Only S0 mode is susceptible to the inter-laminar defects in the varying thickness region.