本文引用Ohguchi等人的實驗數據，以Lee and Shieh對60/40鉛錫合金之內涵時間黏塑性理論延伸到Sn/3.5Ag/0.75Cu銲錫材料。由實驗中不同應變率之應力-應變遲滯曲線，找出理論中所需之材料參數及材料函數，並建立材料應變敏感函數的數學式。
Park等人使用循環混合負載模式對Sn/3.5Ag/0.75Cu銲錫進行測試，企圖以多方向的負載角度來測試錫球之循環受損程度。為了模擬不同負載角度的實驗結果，本文將理論中的內涵時間累積量改寫為與負載角度相關之函數，並決定立方對稱之材料參數及材料函數，模擬結果與實驗相當吻合。本文藉由前述之實驗，建立軸向及剪向的損傷因子與循環圈數之關係式，利用Lemaitre提出的應變等量原理，將損傷因子引入內涵時間黏塑性本構方程式中進行計算，模擬Sn/3.5Ag/0.75Cu銲錫受循環混合負載下之疲勞力－位移反應。於20％、50％及70％之負載下降率疲勞遲滯曲線中，本理論得到相當良好的模擬結果，並對此材料於不同循環負載角度下之臨界損傷因子值進行討論。

In this paper, experimental data of Ohguchi et. al. are used to extend the Endochronic cyclic viscoplasticity of eutectic Tin/Lead(60/40) solder alloy by Lee and Shieh to a Lead-free material of Sn/3.5Ag/0.75Cu; Employed the experimental stress-strain hysteresis loops of different strain rates, material parameters and material functions in the theory can be determined and the functional form of strain rate sensitivity can also be established.
Park et. al. used cyclic mixed-mode loading tests on Sn/3.5Ag/0.75Cu solder joints and investigated their degree of cyclic damage. In the Endochronic theory, the accumulation of intrinsic time is proposed first to depend on the loading angle and then cubic symmetric material parameters and material functions are determined. Through previous experiment, relationships of axial and shear damage factor with cycle number can be established. Using Lemaitre’s strain equivalence principle in the endochronic constitutive equation with damage factor, force-displacement response under cyclic mixed-mode loading can be computed. The hysteresis loops computed under 20％、50％ and 70％ load drop are in very good agreement with data. These allow the discussion in the critical values of damage factor under different loading angles.

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