打音法於混凝土非破壞檢測之應用

The application of impact acoustics on the nondestructive testing of concrete structures

劉柏寬(Bo-Kuan Liu)

指導教授 ： 劉佩玲

國立臺灣大學/工學院/應用力學研究所/碩士(2018年)

https://doi.org/10.6342/NTU201801773

摘要

敲擊回音法是一種常見的混凝土非破壞檢測方法，進行量測時，鋼珠敲擊混凝土表面激發應力波，以位移感測器接收表面位移訊號，經由快速傅立葉轉換將時間域訊號轉換為頻率域訊號，再由頻譜尖峰判斷缺陷位置。而打音法也是一種非破壞檢測法，廣泛應用於磁磚脫黏檢測，其實驗步驟與敲擊回音法類似，差別只在於打音法使用麥克風作為感測器，量測混凝土周遭之聲壓訊號，而混凝土振動會帶動空氣振動，所以我們期望使用打音法得到與敲擊回音法相近之結果。
本文先以有限元素法軟體建立混凝土連接空氣之流固耦合模型，配合數種試體厚度變化與深度變化之裂縫、鋼筋，量測空氣元素的時間－壓力訊號，利用快速傅立葉轉換進行頻譜分析。並嘗試變化敲擊源與內含物，觀察這些參數改變對於打音法有何影響。數值結果指出，打音法得到之聲壓頻譜於試體尺寸與各個深度之裂縫、鋼筋模型檢測中，得到與敲擊回音法之位移頻譜相似的特徵。在淺層裂縫檢測中，打音法較敲擊回音法準確，淺層鋼筋則較差，而較大厚度模型之尺寸檢測則因模態振動導致聲壓頻譜較難判讀，為打音法之限制。
最後進行模型試驗證打音法於混凝土非破壞檢測之可行性。經由實驗結果發現，透過頻譜，打音法可觀測到試體厚度與裂縫、鋼筋之回波訊號，換算其深度與實際值吻合。與敲擊回音法結果比較可知，聲音訊號於實際情況中較位移訊號容易受到外界因素干擾，導致訊號有較大幅度地變動。另外，使用一般桌上型電腦進行量測，也能觀測到特徵。
藉由實驗與數值證實，打音法於混凝土非破壞檢測中，是一種有效且方便的方法。

關鍵字

打音法 ； 非破壞檢測 ； 鋼筋混凝土 ； 裂縫

並列摘要

Impact acoustic has been used in dection of tile bonding,it is rare for the detection of concrete defects.Impact acoustic applies the Fast Fourier to the change of air pressure due to an impact of a steel ball and the defect position is judged by spectrum.
The purpose of this study is to explore the feasibility of the application of impact acoustic in concrete.By tapping steel ball,part of voice come from free vibration and resonace of concrete.Concrete containing cracks or steelthe change vibration mode so it is speculated that impact acoustic can be used in detection.
To confirmed the feasibility of the application of impact acoustic on concrete defection,finite element method is used to establish the model of concrete and air,containing cracks and steel with several kinds of depth.By changing the diameter of impact source,we try to find the limit of impact acoustic in concrete.The results of numerical simulation show that this method has high accurary in the detection of concrete containing cracks and steel in each depth.The results from impact acoustic are better than that from impact echo in shallow steel detection bars,however,it is poor in shallow crack detection.
Finally,the results of numerical simulation are verified by model test.It is found that singals of crack and steel bar can be observed by spectrum.Compared to impact echo,sound waves are disturbed by environmental situation easily resulting in significant changes.In addition,the those features can be observed by measurement of general desktop.This is,impact acoustic is suitable for poor experimental instrument.
Key Word:Impact Acoustic; Nondestructive Method; Crack; Reinforcing Bar

並列關鍵字

Impact Acoustic ； Nondestructive Method ； Crack ； Reinforcing Bar

參考文獻

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