飛機上電纜線支撐架之可靠度研究

Abstract

飛航安全一直是世界各國所重視之議題，了解飛航事故肇因，可避免相同事故再度發生，更有助於爾後之飛航安全。本研究即著眼於此，針對一起因機艙內電纜線支撐架斷落造成冒煙、起火之飛航事故進行研究與分析，研究範疇包括該電纜線支撐架受靜態負載之失效分析、支撐架受反覆負載之疲勞分析與支撐架基底受不確定負載之隨機振動分析。前兩者之研究方法主要在導入量化可靠度的概念，藉由蒙地卡羅模擬與有限元素分析軟體計算，求得支撐架失效機率以及其受反覆負載所造成疲勞破壞之平均失效時間；而後者主要係應用模態分析與隨機振動理論，估算支撐架之自然頻率及其可能之隨機響應。本研究針對電纜線支撐架的力學分析結果顯示，在靜態分析方面，當該類電纜線支撐架所受到的不確定負載呈常態機率分佈且平均值與標準差分別為44.5 N與4.45 N時，其失效機率為4.07×10-12；如在反覆負載的考量下，該類支撐架之平均失效時間為441,512個負載週次；而在模態與隨機振動分析方面，考慮該類結構幾個主要自然頻率範圍，當支撐架受頻寬為0至3,000 Hz、頻譜密度大小為816.88 (mm/s2)2/Hz的帶限白噪音訊號作用，其失效機率為8.07×10-7。綜合以上結果，本研究推論，就力學觀點而言，當該類電纜線支撐架平均負載低於44.5 N時，應為安全之設計。

Aviation safety is a very important issue in the world. Raising the ability for investigating aviation accidents can improve the aviation safety greatly. The major purpose of the present thesis focuses on a case study of a smoke-and-fire accident occurred in an airplane caused by a broken standoff that supports a few electrical cables. Mechanics behaviors of the standoff are studied in three aspects including static, fatigue, and random vibration analysis. Finite element analysis is employed and the loading uncertainty is taken into consideration. Reliability analysis is also included to accounts for the output uncertainties and quantifies the analytical results. Under reasonable and appropriate assumptions including a mean load of 44.5 N and a standard deviation of 4.45 N, it is found that failure probability of the standoff is 4.07×10-12 if static analysis is considered, and its fatigue life is 441,512 cycles if fluctuating loads are considered. As for the random vibration analysis, it is found that the first few natural frequencies of the standoff lie in the range between 0 and 3,000 Hz. If the base of the standoff is subjected to a band-limited white noise excitation within this range and having a constant magnitude of 816.88 (mm/s2)2/Hz, the failure probability of the standoff is 8.07×10-7. From all studied three mechanics aspects, it is concluded that the studied standoff should be safe when subjected to an average load of 44.5 N or lower.