隨機負荷下之疲勞裂縫延伸與疲勞可靠度分析

中山科學研究院品質保證中心摘要本文主要目的在發展一套簡單正確的數學模式來預測隨機負荷作用下之疲勞裂縫延伸趨勢，並依據機率與統計的觀念來分析裂縫成長曲線的變異情形以估測材料在一些隨機循環作用後之可靠度值。在透過分析模式與實驗結果的相互驗證後，本文有下列重要的結論：一、裂紋成長曲線會受隨機負荷峰谷值分佈之影響，二、應用一求得之「等效常振幅負荷」配合裂紋閉合模式能預估出較爲準確的裂縫成長結果，三、利用中間極限值定理與FOSM近似法所作之變異性分析在短裂紋時有較準確之預估，而在長裂紋則趨於保守，四、經過修正之等效常振幅負荷通常能給我們較準確之各項預估。以上諸結論可提供工程設計者於設計受反覆隨機負荷作用之結構物或機械元件一些參考的依據。

關鍵字

隨機負荷；疲勞裂縫；可靠度

並列摘要

In order to predict the fatigue crack growth curve under random loading, a simple analytical model is proposed in this paper. In addition to the mean crack growth curve, the model also considers the statistic variation of the crack growth curves under the same random loading as well as the material reliability after certain loading cycles are applied. To check the applicability of the prediction model, several fatigue experments are performed. After comparing the analytical result with the experimental result, the following conclusions are drawn. (i) Under the same mean value and standard deviation for the stress amplitudes, the fatigue crack growth curves are influenced by the probability density function of the stresses. (ii) An ”equivalent constant loading” and a crack closure model lead to a better prediction than other models. (iii) The variation of the crack growth curves can be predicted accurately for shorter crack lengths and conservatively for longer crack lengths. (iv) The prediction of the statistic variation can be improved by modifying the definition of the equivalent constant loading. The above conclusions can be taken into consideration in designing structural or mechanical components when subjected to loads of random nature.

並列關鍵字

random loading ； fatigue crack ； reliability

國際替代計量

隨機負荷下之疲勞裂縫延伸與疲勞可靠度分析

全文下載

主題瀏覽