結構健康監測技術之目的為早期預警，提早發現損傷並執行維護或修補工作可避免結構失效造成生命財產損失。本文以結構健康監測技術(Structural Health Monitoring, SHM)於金屬單剪力搭接(Single shear lap joint)結構之損傷偵測為主軸，採用智能層(SMART Layer®)系統為基礎，該系統對結構激發藍姆波，並偵測損傷對波傳訊號之影響，以確認損傷是否存在。實驗首先利用飛行時間(time of flight, TOF)確認S0模式藍姆波在金屬單剪力搭接之群速度理論值，再將試件疲勞裂紋成長觀測與SMART Layer®系統偵測結果比較，評估該系統於金屬搭接結構之損傷偵測成效。
SMART Layer®系統之感測器(sensor)與致動器(actuator)皆使用壓電材料鋯鈦酸鉛(Lead Zirconate Titanate, PZT)製作，利用壓電效應為作動原理，即電能與機械能間的交互作用，利用輸入漢寧窗(Hanning window)電壓訊號激發藍姆波訊號，使其於平板傳遞，再由接收端將機械能轉為電壓訊號並加以處理。本系統以損傷指數(Damage index, DI)作為損傷量化之基礎，係經由計算第一抵達波包(First arrival window, FAW)之基線訊號(baseline signal)與散失訊號(scatter signal)能量比值而得。
實驗方面，首先根據研究之實驗試件尺寸建立有限元素模型，依照應力分析結果確認實驗試件最可能產生破壞之區域，針對該區域增貼SMART Layer®感測器佈置，提高損傷被偵測到的機率。本文提出損傷比例(Damage ratio, DR)之概念，由實驗數據發現DR參考值為70%，高於該值即表示裂紋尺寸已達到需注意之程度，應考慮維護或修補。本實驗並以裂紋觀測結果確認實驗DR概念在損傷偵測上具有可信度。由實驗結果得知以SMART Layer®系統DI為基礎計算之DR可與裂紋觀測結果相呼應，驗證SMART Layer®系統可有效偵測金屬單剪力搭接結構之損傷行為。

The purpose of the structural health monitoring (SHM) aims at the early warning when monitoring damages in structures. Once the damages found in the structures, the maintenance or repair can be conducted to avoid structural failure, which may causes catastrophe in human lives and properties. In this study, the experiments on single shear lap joint metallic structures based on the SMART® Layer system were presented. This system can excite a Lamb wave propagating on the structure. The signal is then detected by the system to identify the existence of the damage as the wave propagation altered by the damage. In the experiments, to validate the group velocity of Lamb wave in single shear lap joint metallic structure, theoretical time of flight (TOF) of S0 mode Lamb wave was calculated and compared with experiment results. The performance of the system on monitoring the damage in metallic single lap joint was evaluated by comparing the fatigue crack observations.
The transducers used in the SMART® Layer system are made of piezoelectric materials (Lead Zirconate Titanate, PZT). Based on the piezoelectric effect, which is the coupling between electrical energy and mechanical energy, the Lamb wave is excited by inputting Hanning window signal. The Lamb wave propagates in the plate-like structure and then is detected by a sensor. The mechanical energy is converted to voltage signal for analyzing. Based on the damage index (DI), the damages in structures is evaluated by calculating the baseline signal and scatter signal of first arrival window (FAW).
In the experiments, the finite element analysis was conducted to obtain the stress distribution. The areas with maximum stresses are potential crack initiation cites. The transducers are mounted near such areas to increase the detectability.
In this study, the concept of Damage Ratio (DR) was presented. Based on the experimental data, a DR reference value of 70% was proposed. For a damaged structure, if DR is higher than this reference value, a necessary action to the structure such as maintenance or repair should be taken. The observations of the fatigue cracks were also compared with the DR criterion. The comparisons showed that DR is a reliable parameter for monitoring damages in metallic single shear lap joints.

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