中文摘要：
	本研究主旨在探討平均應力對沃斯回火球墨鑄鐵(ADI)在應變控制下低週疲勞行為之影響，並嘗試以各種平均應力對壽命影響的關係式來了解ADI在不同應變比作用下應變振幅與壽命的關係。實驗結果顯示，在應變比為-1的低週疲勞試驗中，經300 ℃沃斯回火熱處理的ADI有較佳的低週疲勞強度，在應變比為0與0.5時，則是經360 ℃沃斯回火熱處理的ADI有較佳的低週疲勞強度。此外，本研究亦依修正型SWT關係式將ADI在不同熱處理及平均應力條件組合作用下的低週疲勞壽命，迴歸得到較佳的壽命預估公式。
Abstract：
	This study investigated the effects of mean stress on the low-cycle fatigue (LCF) strength of austempered ductile iron (ADI). Uniaxial LCF tests were conducted under strain control with three strain ratios R=-1, 0 and 0.5 at several strain amplitudes in cyclic loading. For a given austempering treatment, the LCF life was decreased with an increase in the strain ratio. Under a strain ratio of -1 the LCF strength of ADI austempered at 300 ℃ was greater than that of ADI austempered at 360 ℃, while the trend was reversed for strain ratios of 0 and 0.5. The LCF data obtained under various combinations of austempering conditions and strain ratios could be well correlated by a modified SWT approach.