構件承受超音波及衝擊之動態應力分析

Dynamic Stress Analysis of Structural Components under Ultrasonic Wave and Impact

蔡英煌(Ying-Huang Tsai)

指導教授 ： 王偉中

國立清華大學/工學院/動力機械工程學系/博士(2007年)

https://doi.org/10.6843/NTHU.2007.00099

摘要

本文是以數位光彈法為基礎，架設一套數位動態光彈系統來拍攝動態光彈條紋。首先觀測矩形平板在超音波激振後所形成的駐波及熱應力，以了解均勻喇叭在工作時的應力狀態；超音波的應用範圍極廣，在工業生產領域中常可發現超音波的應用，唯有充分了解並妥善運用，才能提昇製程中的效率與品質。接著研究含切口之矩形平板在超音波激振下的應力波場及其尖端的應力集中現象，藉以開發超音波加工應用於光電半導體製程中。最後，探討常見之T狀結構受到衝擊後的應力波傳；衝擊波對結構產生影響通常發生於撞擊或地震時，常產生關鍵性的破壞，為能確保設計上的安全性，須對衝擊波所產生的應力集中效應有所了解。
當物體受到超音波或衝擊波時所產生的應力波將異於一般傳統的靜態應力分布，非常適合以光彈法來做全域式的即時觀測，再佐以有限單元法的分析結果，可獲得全盤的了解以利研究。如此不但能提高超音波加工的效能，開發新的超音波加工技術，並有助於評估結構在動態負荷下的安全性。
在運用光彈法觀測駐波應力場的過程中，提出均時光彈性(Time-Averaged Photoelasticity)理論，並利用實驗光彈影像的灰階分布來驗證所推導之理論；此實驗方法可有效節省實驗時間及經費。

關鍵字

動態光彈法 ； 有限元素法 ； 超音波 ； 衝擊波 ； 喇叭 ； 應力集中

並列摘要

Based on the conventional digital photoelastic method, this dissertation developed a digital dynamic photoelastic system to record the dynamic photoelastic fringe patterns. First, the system can be used to observe the stress distributions of standing wave and thermal stress generated by the ultrasonic wave. In the field of industrial production, the application of the ultrasonic wave can be found frequently. Only after sufficient understanding and proper practice of the ultrasonic wave, the efficiency and quality of the production can be improved. Next, the states of stresses in several photoelastic strips with different sizes of V-notches under the incidence of the ultrasonic wave were investigated. The obtained results are useful when applying the ultrasonic wave in the optoelectronic semiconductor industry. Finally, the dynamic photoelastic system was used to investigate the stress wave of T-shape structural components under impact. The dynamic loading usually causes critical damage of the structures during impact or earthquake. To ensure safety, it is necessary to analyze the stress concentration effect of structures under impact.
When the object is affected by the ultrasonic wave or impact, the generated stress wave is different from the conventional static stress distribution. For whole field and real time observation, the dynamic photoelastic method is the best method to investigate this problem. With the aid of finite element method, complete understanding can be obtained and further research can be performed. In addition, the efficiency of the ultrasonic machining can be improved, new fields of the ultrasonic machining technology can be developed, and evaluation of the safety of the structures under dynamic load can be facilitated.
In this dissertation, the time-averaged photoelastic method was proposed. By comparing the gray level distributions of the proposed theory and experimentally obtained photoelastic fringe pattern generated by standing wave only, the correctness of the time-averaged photoelastic method was verified. By using this new method, stress characteristics of a harmonic wave motion can be readily obtained and the experimental procedures are much simplified.

並列關鍵字

dynamic photoelastic method ； finite element method ； ultrasonic wave ； impact ； horn ； stress concentration

參考文獻

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