本研究利用動態敲擊試驗的方式探討構件因材料瑕疵而導致力學性質下降之關係。此試驗可求得不同構件材料在不同邊界條件下之自然頻率 、阻尼係數D及勁度k值,並比較於試體有無瑕疵行為時,其力學參數k及E之差異。 本試驗結果顯示振動頻率會因為試體具有瑕疵性質而降低,尤其當試體底部出現裂縫時其下降最為顯著。此外對於孔洞及埋設紙張試體則較無明顯下降之趨勢,其原因在於瑕疵部位作落於試體之中性軸上,因此較無法呈現出明顯之下降關係。 由試驗結果得知,對於探討力學參數k、E下降比例之關係,裂縫瑕疵其下降比例為8.5%~61.8%,孔洞瑕疵為0.2%~37.4%,紙張瑕疵為7.1%~31.8%。本研究初步認為動態敲擊實驗可能成為營建材料品質驗證之非破壞檢測之ㄧ種。
The study was conducted to investigate the effects of material defect and/or deterioration on the mechanical properties of structural elements using dynamic plunking test. A series of tests were designed and conducted on modeled structural elements made of 5 selected materials with two types of boundary condition (simple support and cantilever) to study the resulted change of dynamic properties including natural frequency, fn, damping ratio D, stiffness k of structural element, and Young’s modulus E of the material. The results of the tests indicated that natural frequency decreases due to defect/deterioration, which is especially significant for the specimens with fissures on the surface of the specimen. The results also indicated that the decreases of frequency for specimens with small openings or pieces of thin paper embedded within are much less significant because that the defects locate on the neutral axis of the vibration. Specifically, the test results exhibited that the reduction of the mechanical properties of the tested structural elements is 8.5-61.8% for fissures at the specimen surface, 0.2-37.4% for openings within specimen body, and 7.1-31.8% for pieces of paper embedded in the middle of the specimen. In general, the results of the study indicated clear influence of defect/deterioration on the studied dynamic properties of the structural elements tested with the plunking method which can be a useful tool as a type of non-destruction test for construction material quality inspection/verification in the future.
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