7005擠製鋁合金的拉伸與疲勞性質研究

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Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/2010

Title:	7005擠製鋁合金的拉伸與疲勞性質研究
Authors:	鍾昆原;Kun-Yun Zho
Contributors:	機械工程研究所
Keywords:	7005;多角化;動態回復;動態再結晶;可靠度;7005;poligonization;dynamic recovery;dynamic recrystallization;reliability
Date:	2002-01-18
Issue Date:	2009-09-21 11:36:18 (UTC+8)
Publisher:	國立中央大學圖書館
Abstract:	本研究的主要目的在於探討鋁合金7005擠製件的拉伸與疲勞性質。在拉伸性質方面，討論高應變速率(1.85x10-2 s-1)及低應變速率(1.85x10-4 s-1)對拉伸強度、降伏強度及伸長率的影響，分析微結構變化對拉伸性質造成的差異。實驗結果顯示，高應變速率下應變硬化效果顯著，得到較高的拉伸強度及降伏強度；低應變速率下由於動態回復的多角化過程，得到次晶粒受應力作用拉長，因此有較高的伸長率。疲勞性質方面，分析兩種高低反覆應力(240 MPa、180 MPa)的破壞模式與微結構改變之間的關係。實驗結果顯示，存在於試棒表面附近的介在物顆粒對疲勞壽命有很大的影響。在塑性變形過程中，若發生動態回復、多角化的現象，使晶粒軟化，疲勞裂縫呈現穿晶破壞模式，出現疲勞紋；若發生動態再結晶的現象，會出現細小的晶粒，疲勞裂縫呈現沿晶破壞，可以看到粗糙的破壞表面。最後利用可靠度統計分析中常用的韋伯分布函數來討論疲勞的破壞機率，並做疲勞壽命預測。 The aim of this study was to investigate the tensile and fatigue properties of as- extruded aluminum alloy, 7005. Regrading to tensile properties, specimens were tested at higher strain rate (1.85x10-2 s-1) and lower strain rate (1.85x10-4 s-1) and showed the effects on the UTS, YS and elongation. As the experimental results indicated, the strain hardening effect under higher strain rate was more obvious and both the UTS and YS were higher. The polygonization of dynamic recovery under lower strain rate deformation resulted in subgrains stretched by tensile stress. So the elongation was higher, too. In the part of fatigue property, the relationship between fractography and microstructure of specimens under two levels of repeated stress(240 MPa、180 MPa) was analyzed. As the experimental results indicated, the existent inclusion particles near specimen surface had a great influence on fatigue life. During the plastic deformation process, if dynamic recovery and polygonization occurred in the specimens, the grains were softened and the fatigue crack was transgranular fracture. Then the fatigue striations showed. If dynamic recrystallization occurred, the microstructure showed fine grains and the fatigue crack was intergranular fracture. The rough fracture surface was observed. Finally the statistical analysis of reliability, Weibull distribution function, was utilized to predict the fracture probability and fatigue life.
Appears in Collections:	[Graduate Institute of Mechanical Engineering] Electronic Thesis & Dissertation

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