應用隨機疲勞裂縫成長模型探討飛機蒙皮多部位損傷行為

Abstract

飛航安全為一相當重要且受廣泛討論的議題，而老舊飛機蒙皮廣佈疲勞裂縫影響飛航安全甚劇，若能了解蒙皮裂縫成長如何影響飛航安全並加以提防，對飛航安全將有相當程度的提升。著眼於此，本研究以三種簡化情境探討飛機蒙皮在多部位損傷考量下的裂縫成長行為。首先，從疲勞試驗結果可知2024-T351鋁合金之疲勞裂縫成長存在一些不確定性，本論文以Paris-Erdogan law與Yang and Manning’s law兩種模型描述裂縫成長及其不確定性，並透過單一裂縫之疲勞試驗結果尋找模型中所需的參數，隨後透過文獻提及的方法修正Paris-Erdogan law應力強度因子的表示式，以預估多部位損傷下的裂縫成長情形，並與考慮互制之Paris-Erdogan law分析結果比對。此外為了探討裂縫互制對於裂縫成長之影響，本文以Yang and Manning’s law來描述不考慮裂縫間互制之多部位損傷裂縫成長情形，並與考慮互制效果之Paris-Erdogan law結果對照。依據本文設定情境之預估結果得知，前述兩者平均失效週次最大差達21％；而在諸多考量因素中，初始裂縫長度對失效週次影響甚大，特別的，當鉚釘孔處之初始裂縫尖端間距相等時，等長初始裂縫情況下的失效週次最少。

Aviation safety is a very important research topic and has been studied extensively. Widespread fatigue cracks on the skin of an airplane affect aviation safety significantly and deserve to be investigated from various aspects. Widespread fatigue cracks can be considered a multiple-site damage (MSD) problem. In the present thesis, MSD on aircraft skin is studied by considering three simplified configurations. Since there is uncertainty in 2024-T351 Al alloy single-crack fatigue growth test, a randonmized Paris-Erdogan law and Yang and Manning’s law are employed respectively to describe the crack growth behavior as well as its uncertainty. The stress intensity factor range in Paris-Erdogan law for single crack condition is modified appropriately for MSD conditions. The effect of interaction between cracks is emphasized and investigated in detail, and the analysis based on Yang and Manning’s law is considered conditions without interaction. It is found that the decrease of fatigue life can be as large as 21% when considering interaction effect. It is also found that fatigue life is influenced very much by the initial crack length as well as multiple crack .