建立穩態磁滯環新描述方法於腐蝕疲勞之應用

Development of the New Descriptive Approach to Stable Hysteresis Loop Applied in Corrosion-Fatigue

機械元件耐久性設計，須考量到材料特性與負載特性外，還必須考量到環境特性如耐蝕性等。鋁合金材料具有質輕、高強度等特性，因此經常被應用在航空器、汽車、壓力容器等。其中鍛造用鋁合金具有高耐蝕性與強度，是機械元件製造上常被選用的金屬材料。本文以1070 鋁合金，進行理論推導，模擬在周次應變振幅負載下的穩態應力應變遲滯環，進一步由穩態遲滯環計算出材料每周次所吸收塑性應變能△Wp，再根據材料的塑性應變能疲勞壽命曲線（△Wp -Nf curve），預估材料的疲勞壽命（Nf）。經由實驗數據與使用本文理論計算結果，可顯示出實驗與理論計算值兩者之間有良好的吻合程度，確立本文所提出方法的正確性。

For a component subject to repeated loading, the characters of metal and loading history are major consideration in the design of fatigue life. But, service environment effect is not negligible. It is well known that corrosive environment is detrimental to fatigue life. The Al alloy for forging that has high strength and good corrosion-fatigue resistance is usually used in many applications such as aircraft, vehicle and pressure vessel. For 1070 Al alloy, this study presents a set of algebraic equations to simulate the stable hysteresis loop under constant strain rate. Furthermore, the stable plastic strain energy per cycle is determined by integrating the enclosed area in the stable hysteresis loop. According the stable plastic strain energy-life curve of the 1070 Al alloy, the fatigue life can be predicted. It is found that the data generated by the proposed methods are in qualitative agreement with the experimental data. Thus, the validity of the proposed methods is confirmed.